Add a security hook that allows a LSM to be notified when a task gets a fatal signal. This patch is a previous step on the way to compute the task crash period by the "brute" LSM (linux security module to detect and mitigate fork brute force attack against vulnerable userspace processes).

Signed-off-by: John Wood john.wood@gmx.com Reviewed-by: Kees Cook keescook@chromium.org --- include/linux/lsm_hook_defs.h | 1 + include/linux/lsm_hooks.h | 4 ++++ include/linux/security.h | 4 ++++ kernel/signal.c | 1 + security/security.c | 5 +++++ 5 files changed, 15 insertions(+)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index 04c01794de83..e28468e84300 100644 --- a/include/linux/lsm_hook_defs.h +++ b/include/linux/lsm_hook_defs.h @@ -225,6 +225,7 @@ LSM_HOOK(int, -ENOSYS, task_prctl, int option, unsigned long arg2, unsigned long arg3, unsigned long arg4, unsigned long arg5) LSM_HOOK(void, LSM_RET_VOID, task_to_inode, struct task_struct *p, struct inode *inode) +LSM_HOOK(void, LSM_RET_VOID, task_fatal_signal, const kernel_siginfo_t *siginfo) LSM_HOOK(int, 0, ipc_permission, struct kern_ipc_perm *ipcp, short flag) LSM_HOOK(void, LSM_RET_VOID, ipc_getsecid, struct kern_ipc_perm *ipcp, u32 *secid) diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index 5c4c5c0602cb..fc8bef0f15d9 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -799,6 +799,10 @@ * security attributes, e.g. for /proc/pid inodes. * @p contains the task_struct for the task. * @inode contains the inode structure for the inode. + * @task_fatal_signal: + * This hook allows security modules to be notified when a task gets a + * fatal signal. + * @siginfo contains the signal information. * * Security hooks for Netlink messaging. * diff --git a/include/linux/security.h b/include/linux/security.h index 06f7c50ce77f..609c76c6c764 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -433,6 +433,7 @@ int security_task_kill(struct task_struct *p, struct kernel_siginfo *info, int security_task_prctl(int option, unsigned long arg2, unsigned long arg3, unsigned long arg4, unsigned long arg5); void security_task_to_inode(struct task_struct *p, struct inode *inode); +void security_task_fatal_signal(const kernel_siginfo_t *siginfo); int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag); void security_ipc_getsecid(struct kern_ipc_perm *ipcp, u32 *secid); int security_msg_msg_alloc(struct msg_msg *msg); @@ -1183,6 +1184,9 @@ static inline int security_task_prctl(int option, unsigned long arg2, static inline void security_task_to_inode(struct task_struct *p, struct inode *inode) { }

+static inline void security_task_fatal_signal(const kernel_siginfo_t *siginfo) +{ } + static inline int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag) { diff --git a/kernel/signal.c b/kernel/signal.c index 66e88649cf74..62625ad98b14 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2787,6 +2787,7 @@ bool get_signal(struct ksignal *ksig) /* * Anything else is fatal, maybe with a core dump. */ + security_task_fatal_signal(&ksig->info); current->flags |= PF_SIGNALED;

if (sig_kernel_coredump(signr)) { diff --git a/security/security.c b/security/security.c index b38155b2de83..208e3e7d4284 100644 --- a/security/security.c +++ b/security/security.c @@ -1891,6 +1891,11 @@ void security_task_to_inode(struct task_struct *p, struct inode *inode) call_void_hook(task_to_inode, p, inode); }

+void security_task_fatal_signal(const kernel_siginfo_t *siginfo) +{ + call_void_hook(task_fatal_signal, siginfo); +} + int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag) { return call_int_hook(ipc_permission, 0, ipcp, flag); -- 2.25.1

For a correct management of a fork brute force attack it is necessary to track all the information related to the application crashes. To do so, use the extended attributes (xattr) of the executable files and define a statistical data structure to hold all the necessary information shared by all the fork hierarchy processes. This info is the number of crashes, the last crash timestamp and the crash period's moving average.

The same can be achieved using a pointer to the fork hierarchy statistical data held by the task_struct structure. But this has an important drawback: a brute force attack that happens through the execve system call losts the faults info since these statistics are freed when the fork hierarchy disappears. Using this method makes not possible to manage this attack type that can be successfully treated using extended attributes.

Also, to avoid false positives during the attack detection it is necessary to narrow the possible cases. So, only the following scenarios are taken into account:

1.- Launching (fork()/exec()) a setuid/setgid process repeatedly until a desirable memory layout is got (e.g. Stack Clash). 2.- Connecting to an exec()ing network daemon (e.g. xinetd) repeatedly until a desirable memory layout is got (e.g. what CTFs do for simple network service). 3.- Launching processes without exec() (e.g. Android Zygote) and exposing state to attack a sibling. 4.- Connecting to a fork()ing network daemon (e.g. apache) repeatedly until the previously shared memory layout of all the other children is exposed (e.g. kind of related to HeartBleed).

In each case, a privilege boundary has been crossed:

Case 1: setuid/setgid process Case 2: network to local Case 3: privilege changes Case 4: network to local

To mark that a privilege boundary has been crossed it is only necessary to create a new stats for the executable file via the extended attribute and only if it has no previous statistical data. This is done using four different LSM hooks, one per privilege boundary:

setuid/setgid process --> bprm_creds_from_file hook (based on secureexec flag). network to local -------> socket_accept hook (taking into account only external connections). privilege changes ------> task_fix_setuid and task_fix_setgid hooks.

To detect a brute force attack it is necessary that the executable file statistics be updated in every fatal crash and the most important data to update is the application crash period. To do so, use the new "task_fatal_signal" LSM hook added in a previous step.

The application crash period must be a value that is not prone to change due to spurious data and follows the real crash period. So, to compute it, the exponential moving average (EMA) is used.

Based on the updated statistics two different attacks can be handled. A slow brute force attack that is detected if the maximum number of faults per fork hierarchy is reached and a fast brute force attack that is detected if the application crash period falls below a certain threshold.

Moreover, only the signals delivered by the kernel are taken into account with the exception of the SIGABRT signal since the latter is used by glibc for stack canary, malloc, etc failures, which may indicate that a mitigation has been triggered.

Signed-off-by: John Wood john.wood@gmx.com --- include/uapi/linux/xattr.h | 3 + security/brute/brute.c | 478 +++++++++++++++++++++++++++++++++++++ 2 files changed, 481 insertions(+)

diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h index 9463db2dfa9d..ce1c8497dceb 100644 --- a/include/uapi/linux/xattr.h +++ b/include/uapi/linux/xattr.h @@ -76,6 +76,9 @@ #define XATTR_CAPS_SUFFIX "capability" #define XATTR_NAME_CAPS XATTR_SECURITY_PREFIX XATTR_CAPS_SUFFIX

+#define XATTR_BRUTE_SUFFIX "brute" +#define XATTR_NAME_BRUTE XATTR_SECURITY_PREFIX XATTR_BRUTE_SUFFIX + #define XATTR_POSIX_ACL_ACCESS "posix_acl_access" #define XATTR_NAME_POSIX_ACL_ACCESS XATTR_SYSTEM_PREFIX XATTR_POSIX_ACL_ACCESS #define XATTR_POSIX_ACL_DEFAULT "posix_acl_default" diff --git a/security/brute/brute.c b/security/brute/brute.c index 0edb89a58ab0..66db0dd0664d 100644 --- a/security/brute/brute.c +++ b/security/brute/brute.c @@ -2,8 +2,85 @@

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

+#include <linux/binfmts.h> #include <linux/lsm_hooks.h> #include <linux/sysctl.h> +#include <linux/xattr.h> +#include <net/ipv6.h> +#include <net/sock.h> + +/** + * struct brute_stats - Fork brute force attack statistics. + * @faults: Number of crashes. + * @nsecs: Last crash timestamp as the number of nanoseconds in the + * International Atomic Time (TAI) reference. + * @period: Crash period's moving average. + * @flags: Statistics flags as a whole. + * @not_allowed: Not allowed executable file flag. + * @unused: Remaining unused flags. + * + * This structure holds the statistical data shared by all the fork hierarchy + * processes. + */ +struct brute_stats { + u32 faults; + u64 nsecs; + u64 period; + union { + u8 flags; + struct { + u8 not_allowed : 1; + u8 unused : 7; + }; + }; +}; + +/** + * struct brute_raw_stats - Raw fork brute force attack statistics. + * @faults: Number of crashes. + * @nsecs: Last crash timestamp as the number of nanoseconds in the + * International Atomic Time (TAI) reference. + * @period: Crash period's moving average. + * @flags: Statistics flags. + * + * This structure holds the statistical data on disk as an extended attribute. + * Since the filesystems on which extended attributes are stored might also be + * used on architectures with a different byte order and machine word size, care + * should be taken to store attribute values in an architecture-independent + * format. + */ +struct brute_raw_stats { + __le32 faults; + __le64 nsecs; + __le64 period; + u8 flags; +} __packed; + +/** + * brute_get_current_exe_file() - Get the current task's executable file. + * + * Since all the kernel threads associated with a task share the same executable + * file, get the thread group leader's executable file. + * + * Context: The file must be released via fput(). + * Return: NULL if the current task has no associated executable file. A pointer + * to the executable file otherwise. + */ +static struct file *brute_get_current_exe_file(void) +{ + struct task_struct *task = current; + struct file *exe_file; + + rcu_read_lock(); + if (!thread_group_leader(task)) + task = rcu_dereference(task->group_leader); + get_task_struct(task); + rcu_read_unlock(); + + exe_file = get_task_exe_file(task); + put_task_struct(task); + return exe_file; +}

/** * DOC: brute_ema_weight_numerator @@ -19,6 +96,18 @@ static unsigned int brute_ema_weight_numerator __read_mostly = 7; */ static unsigned int brute_ema_weight_denominator __read_mostly = 10;

+/** + * brute_mul_by_ema_weight() - Multiply by EMA weight. + * @value: Value to multiply by EMA weight. + * + * Return: The result of the multiplication operation. + */ +static inline u64 brute_mul_by_ema_weight(u64 value) +{ + return mul_u64_u32_div(value, brute_ema_weight_numerator, + brute_ema_weight_denominator); +} + /** * DOC: brute_max_faults * @@ -30,6 +119,56 @@ static unsigned int brute_ema_weight_denominator __read_mostly = 10; */ static unsigned int brute_max_faults __read_mostly = 200;

+/** + * brute_update_crash_period() - Update the application crash period. + * @stats: Statistics that hold the application crash period to update. Cannot + * be NULL. + * + * The application crash period must be a value that is not prone to change due + * to spurious data and follows the real crash period. So, to compute it, the + * exponential moving average (EMA) is used. + * + * This kind of average defines a weight (between 0 and 1) for the new value to + * add and applies the remainder of the weight to the current average value. + * This way, some spurious data will not excessively modify the average and only + * if the new values are persistent, the moving average will tend towards them. + * + * Mathematically the application crash period's EMA can be expressed as + * follows: + * + * period_ema = period * weight + period_ema * (1 - weight) + * + * If the operations are applied: + * + * period_ema = period * weight + period_ema - period_ema * weight + * + * If the operands are ordered: + * + * period_ema = period_ema - period_ema * weight + period * weight + * + * Finally, this formula can be written as follows: + * + * period_ema -= period_ema * weight; + * period_ema += period * weight; + */ +static void brute_update_crash_period(struct brute_stats *stats) +{ + u64 current_period; + u64 now = ktime_get_clocktai_ns(); + + if (stats->faults >= (u32)brute_max_faults) + return; + + if (stats->nsecs) { + current_period = now > stats->nsecs ? now - stats->nsecs : 0; + stats->period -= brute_mul_by_ema_weight(stats->period); + stats->period += brute_mul_by_ema_weight(current_period); + } + + stats->nsecs = now; + stats->faults += 1; +} + /** * DOC: brute_min_faults * @@ -51,6 +190,343 @@ static unsigned int brute_min_faults __read_mostly = 5; */ static unsigned int brute_crash_period_threshold __read_mostly = 30;

+/** + * brute_attack_running() - Test if a brute force attack is happening. + * @stats: Statistical data shared by all the fork hierarchy processes. Cannot + * be NULL. + * + * The decision if a brute force attack is running is based on the statistical + * data shared by all the fork hierarchy processes. + * + * There are two types of brute force attacks that can be detected using the + * statistical data. The first one is a slow brute force attack that is detected + * if the maximum number of faults per fork hierarchy is reached. The second + * type is a fast brute force attack that is detected if the application crash + * period falls below a certain threshold. + * + * Moreover, it is important to note that no attacks will be detected until a + * minimum number of faults have occurred. This allows to have a trend in the + * crash period when the EMA is used. + * + * Return: True if a brute force attack is happening. False otherwise. + */ +static bool brute_attack_running(const struct brute_stats *stats) +{ + u64 threshold; + + if (stats->faults < (u32)brute_min_faults) + return false; + + if (stats->faults >= (u32)brute_max_faults) + return true; + + threshold = (u64)brute_crash_period_threshold * (u64)NSEC_PER_SEC; + return stats->period < threshold; +} + +/** + * brute_print_attack_running() - Warn about a fork brute force attack. + */ +static inline void brute_print_attack_running(void) +{ + pr_warn("fork brute force attack detected [pid %d: %s]\n", current->pid, + current->comm); +} + +/** + * brute_get_xattr_stats() - Get the stats from an extended attribute. + * @dentry: The dentry of the file to get the extended attribute. + * @inode: The inode of the file to get the extended attribute. + * @stats: The stats where to store the info obtained from the extended + * attribute. Cannot be NULL. + * + * Return: An error code if it is not possible to get the statistical data. Zero + * otherwise. + */ +static int brute_get_xattr_stats(struct dentry *dentry, struct inode *inode, + struct brute_stats *stats) +{ + int rc; + struct brute_raw_stats raw_stats; + + rc = __vfs_getxattr(dentry, inode, XATTR_NAME_BRUTE, &raw_stats, + sizeof(raw_stats)); + if (rc < 0) + return rc; + + stats->faults = le32_to_cpu(raw_stats.faults); + stats->nsecs = le64_to_cpu(raw_stats.nsecs); + stats->period = le64_to_cpu(raw_stats.period); + stats->flags = raw_stats.flags; + return 0; +} + +/** + * brute_set_xattr_stats() - Set the stats to an extended attribute. + * @dentry: The dentry of the file to set the extended attribute. + * @inode: The inode of the file to set the extended attribute. + * @stats: The stats from where to extract the info to set the extended attribute. + * Cannot be NULL. + * + * Return: An error code if it is not possible to set the statistical data. Zero + * otherwise. + */ +static int brute_set_xattr_stats(struct dentry *dentry, struct inode *inode, + const struct brute_stats *stats) +{ + struct brute_raw_stats raw_stats; + + raw_stats.faults = cpu_to_le32(stats->faults); + raw_stats.nsecs = cpu_to_le64(stats->nsecs); + raw_stats.period = cpu_to_le64(stats->period); + raw_stats.flags = stats->flags; + + return __vfs_setxattr(&init_user_ns, dentry, inode, XATTR_NAME_BRUTE, + &raw_stats, sizeof(raw_stats), 0); +} + +/** + * brute_update_xattr_stats() - Update the stats of a file. + * @file: The file that holds the statistical data to update. Cannot be NULL. + * + * For a correct management of a fork brute force attack it is only necessary to + * update the statistics and test if an attack is happening based on these data. + * It is important to note that if the file has no stats nothing is updated nor + * created. This way, the scenario where an application has not crossed any + * privilege boundary is avoided since the existence of the extended attribute + * denotes the crossing of bounds. + */ +static void brute_update_xattr_stats(const struct file *file) +{ + struct dentry *dentry = file_dentry(file); + struct inode *inode = file_inode(file); + struct brute_stats stats; + int rc; + + inode_lock(inode); + rc = brute_get_xattr_stats(dentry, inode, &stats); + WARN_ON_ONCE(rc && rc != -ENODATA); + if (rc) { + inode_unlock(inode); + return; + } + + brute_update_crash_period(&stats); + if (brute_attack_running(&stats)) { + brute_print_attack_running(); + stats.not_allowed = true; + } + + rc = brute_set_xattr_stats(dentry, inode, &stats); + WARN_ON_ONCE(rc); + inode_unlock(inode); +} + +/** + * brute_reset_stats() - Reset the statistical data. + * @stats: Statistics to be reset. Cannot be NULL. + */ +static inline void brute_reset_stats(struct brute_stats *stats) +{ + memset(stats, 0, sizeof(*stats)); +} + +/** + * brute_new_xattr_stats() - New statistics for a file. + * @file: The file in which to create the new statistical data. Cannot be NULL. + * + * Only if the file has no statistical data create it. This function will be + * called to mark that a privilege boundary has been crossed so, if new stats + * are required, they do not contain any useful data. The existence of the + * extended attribute denotes the crossing of privilege bounds. + * + * Return: An error code if it is not possible to get or set the statistical + * data. Zero otherwise. + */ +static int brute_new_xattr_stats(const struct file *file) +{ + struct dentry *dentry = file_dentry(file); + struct inode *inode = file_inode(file); + struct brute_stats stats; + int rc; + + inode_lock(inode); + rc = brute_get_xattr_stats(dentry, inode, &stats); + if (rc && rc != -ENODATA) + goto unlock; + + if (rc == -ENODATA) { + brute_reset_stats(&stats); + rc = brute_set_xattr_stats(dentry, inode, &stats); + if (rc) + goto unlock; + } + +unlock: + inode_unlock(inode); + return rc; +} + +/** + * brute_current_new_xattr_stats() - New stats for the current task's exe file. + * + * Return: An error code if it is not possible to get or set the statistical + * data. Zero otherwise. + */ +static int brute_current_new_xattr_stats(void) +{ + struct file *exe_file; + int rc; + + exe_file = brute_get_current_exe_file(); + if (WARN_ON_ONCE(!exe_file)) + return -ENOENT; + + rc = brute_new_xattr_stats(exe_file); + WARN_ON_ONCE(rc); + fput(exe_file); + return rc; +} + +/** + * brute_signal_from_user() - Test if a signal is coming from userspace. + * @siginfo: Contains the signal information. + * + * To avoid false positives during the attack detection it is necessary to + * narrow the possible cases. So, only the signals delivered by the kernel are + * taken into account with the exception of the SIGABRT signal since the latter + * is used by glibc for stack canary, malloc, etc failures, which may indicate + * that a mitigation has been triggered. + * + * Return: True if the signal is coming from usersapce. False otherwise. + */ +static inline bool brute_signal_from_user(const kernel_siginfo_t *siginfo) +{ + return siginfo->si_signo == SIGKILL && siginfo->si_code != SIGABRT; +} + +/** + * brute_task_fatal_signal() - Target for the task_fatal_signal hook. + * @siginfo: Contains the signal information. + * + * To detect a brute force attack it is necessary, as a first step, to test in + * every fatal crash if the signal is delibered by the kernel. If so, update the + * statistics and act based on these data. + */ +static void brute_task_fatal_signal(const kernel_siginfo_t *siginfo) +{ + struct file *exe_file; + + if (brute_signal_from_user(siginfo)) + return; + + exe_file = brute_get_current_exe_file(); + if (WARN_ON_ONCE(!exe_file)) + return; + + brute_update_xattr_stats(exe_file); + fput(exe_file); +} + +/** + * brute_task_execve() - Target for the bprm_creds_from_file hook. + * @bprm: Contains the linux_binprm structure. + * @file: Binary that will be executed without an interpreter. + * + * This hook is useful to mark that a privilege boundary (setuid/setgid process) + * has been crossed. This is done based on the "secureexec" flag. + * + * To be defensive return an error code if it is not possible to get or set the + * stats using an extended attribute since this blocks the execution of the + * file. This scenario is treated as an attack. + * + * It is important to note that here the brute_new_xattr_stats function could be + * used with a previous test of the secureexec flag. However it is better to use + * the basic xattr functions since in a future commit a test if the execution is + * allowed (via the brute_stats::not_allowed flag) will be necessary. This way, + * the stats of the file will be get only once. + * + * Return: An error code if it is not possible to get or set the statistical + * data. Zero otherwise. + */ +static int brute_task_execve(struct linux_binprm *bprm, struct file *file) +{ + struct dentry *dentry = file_dentry(bprm->file); + struct inode *inode = file_inode(bprm->file); + struct brute_stats stats; + int rc; + + inode_lock(inode); + rc = brute_get_xattr_stats(dentry, inode, &stats); + if (WARN_ON_ONCE(rc && rc != -ENODATA)) + goto unlock; + + if (rc == -ENODATA && bprm->secureexec) { + brute_reset_stats(&stats); + rc = brute_set_xattr_stats(dentry, inode, &stats); + if (WARN_ON_ONCE(rc)) + goto unlock; + } + + rc = 0; +unlock: + inode_unlock(inode); + return rc; +} + +/** + * brute_task_change_priv() - Target for the task_fix_setid hooks. + * @new: The set of credentials that will be installed. + * @old: The set of credentials that are being replaced. + * @flags: Contains one of the LSM_SETID_* values. + * + * This hook is useful to mark that a privilege boundary (privilege changes) has + * been crossed. + * + * Return: An error code if it is not possible to get or set the statistical + * data. Zero otherwise. + */ +static int brute_task_change_priv(struct cred *new, const struct cred *old, int flags) +{ + return brute_current_new_xattr_stats(); +} + +/** + * brute_socket_accept() - Target for the socket_accept hook. + * @sock: Contains the listening socket structure. + * @newsock: Contains the newly created server socket for connection. + * + * This hook is useful to mark that a privilege boundary (network to local) has + * been crossed. This is done only if the listening socket accepts external + * connections. The sockets for inter-process communication (IPC) and those that + * are listening on loopback addresses are not taken into account. + * + * Return: An error code if it is not possible to get or set the statistical + * data. Zero otherwise. + */ +static int brute_socket_accept(struct socket *sock, struct socket *newsock) +{ + struct sock *sk = sock->sk; + + if (sk->sk_family == AF_UNIX || sk->sk_family == AF_NETLINK || + sk->sk_rcv_saddr == htonl(INADDR_LOOPBACK) || + ipv6_addr_equal(&sk->sk_v6_rcv_saddr, &in6addr_loopback)) + return 0; + + return brute_current_new_xattr_stats(); +} + +/* + * brute_hooks - Targets for the LSM's hooks. + */ +static struct security_hook_list brute_hooks[] __lsm_ro_after_init = { + LSM_HOOK_INIT(task_fatal_signal, brute_task_fatal_signal), + LSM_HOOK_INIT(bprm_creds_from_file, brute_task_execve), + LSM_HOOK_INIT(task_fix_setuid, brute_task_change_priv), + LSM_HOOK_INIT(task_fix_setgid, brute_task_change_priv), + LSM_HOOK_INIT(socket_accept, brute_socket_accept), +}; + #ifdef CONFIG_SYSCTL static unsigned int uint_max = UINT_MAX; #define SYSCTL_UINT_MAX (&uint_max) @@ -137,6 +613,8 @@ static inline void brute_init_sysctl(void) { } static int __init brute_init(void) { pr_info("becoming mindful\n"); + security_add_hooks(brute_hooks, ARRAY_SIZE(brute_hooks), + KBUILD_MODNAME); brute_init_sysctl(); return 0; } -- 2.25.1

Add tests to check the brute LSM functionality and cover fork/exec brute force attacks crossing the following privilege boundaries:

1.- setuid process 2.- privilege changes 3.- network to local

Also, as a first step check that fork/exec brute force attacks without crossing any privilege boundary already commented doesn't trigger the detection and mitigation stage.

Once a brute force attack is detected, the "test" executable is marked as "not allowed". To start again a new test, use the "rmxattr" app to revert this state. This way, all the tests can be run using the same binary.

Signed-off-by: John Wood john.wood@gmx.com --- tools/testing/selftests/Makefile | 1 + tools/testing/selftests/brute/.gitignore | 2 + tools/testing/selftests/brute/Makefile | 5 + tools/testing/selftests/brute/config | 1 + tools/testing/selftests/brute/rmxattr.c | 34 ++ tools/testing/selftests/brute/test.c | 507 +++++++++++++++++++++++ tools/testing/selftests/brute/test.sh | 256 ++++++++++++ 7 files changed, 806 insertions(+) create mode 100644 tools/testing/selftests/brute/.gitignore create mode 100644 tools/testing/selftests/brute/Makefile create mode 100644 tools/testing/selftests/brute/config create mode 100644 tools/testing/selftests/brute/rmxattr.c create mode 100644 tools/testing/selftests/brute/test.c create mode 100755 tools/testing/selftests/brute/test.sh

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile index bc3299a20338..5c413a010849 100644 --- a/tools/testing/selftests/Makefile +++ b/tools/testing/selftests/Makefile @@ -2,6 +2,7 @@ TARGETS = arm64 TARGETS += bpf TARGETS += breakpoints +TARGETS += brute TARGETS += capabilities TARGETS += cgroup TARGETS += clone3 diff --git a/tools/testing/selftests/brute/.gitignore b/tools/testing/selftests/brute/.gitignore new file mode 100644 index 000000000000..989894615766 --- /dev/null +++ b/tools/testing/selftests/brute/.gitignore @@ -0,0 +1,2 @@ +rmxattr +test diff --git a/tools/testing/selftests/brute/Makefile b/tools/testing/selftests/brute/Makefile new file mode 100644 index 000000000000..c675d1df62ca --- /dev/null +++ b/tools/testing/selftests/brute/Makefile @@ -0,0 +1,5 @@ +# SPDX-License-Identifier: GPL-2.0 +CFLAGS += -Wall -O2 +TEST_PROGS := test.sh +TEST_GEN_FILES := rmxattr test +include ../lib.mk diff --git a/tools/testing/selftests/brute/config b/tools/testing/selftests/brute/config new file mode 100644 index 000000000000..3587b7bf6c23 --- /dev/null +++ b/tools/testing/selftests/brute/config @@ -0,0 +1 @@ +CONFIG_SECURITY_FORK_BRUTE=y diff --git a/tools/testing/selftests/brute/rmxattr.c b/tools/testing/selftests/brute/rmxattr.c new file mode 100644 index 000000000000..9ed90409d337 --- /dev/null +++ b/tools/testing/selftests/brute/rmxattr.c @@ -0,0 +1,34 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include <libgen.h> +#include <stdio.h> +#include <stdlib.h> +#include <sys/xattr.h> + +static __attribute__((noreturn)) void error_failure(const char *message) +{ + perror(message); + exit(EXIT_FAILURE); +} + +#define PROG_NAME basename(argv[0]) + +#define XATTR_SECURITY_PREFIX "security." +#define XATTR_BRUTE_SUFFIX "brute" +#define XATTR_NAME_BRUTE XATTR_SECURITY_PREFIX XATTR_BRUTE_SUFFIX + +int main(int argc, char **argv) +{ + int rc; + + if (argc < 2) { + printf("Usage: %s <FILE>\n", PROG_NAME); + exit(EXIT_FAILURE); + } + + rc = removexattr(argv[1], XATTR_NAME_BRUTE); + if (rc) + error_failure("removexattr"); + + return EXIT_SUCCESS; +} diff --git a/tools/testing/selftests/brute/test.c b/tools/testing/selftests/brute/test.c new file mode 100644 index 000000000000..44c32f446dca --- /dev/null +++ b/tools/testing/selftests/brute/test.c @@ -0,0 +1,507 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include <arpa/inet.h> +#include <errno.h> +#include <libgen.h> +#include <pwd.h> +#include <signal.h> +#include <stdbool.h> +#include <stdint.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <sys/socket.h> +#include <sys/time.h> +#include <sys/types.h> +#include <sys/wait.h> +#include <unistd.h> + +static const char *message = "message"; + +enum mode { + MODE_NONE, + MODE_CRASH, + MODE_SERVER_CRASH, + MODE_CLIENT, +}; + +enum crash_after { + CRASH_AFTER_NONE, + CRASH_AFTER_FORK, + CRASH_AFTER_EXEC, +}; + +enum signal_from { + SIGNAL_FROM_NONE, + SIGNAL_FROM_USER, + SIGNAL_FROM_KERNEL, +}; + +struct args { + uint32_t ip; + uint16_t port; + int counter; + long timeout; + enum mode mode; + enum crash_after crash_after; + enum signal_from signal_from; + unsigned char has_counter : 1; + unsigned char has_change_priv : 1; + unsigned char has_ip : 1; + unsigned char has_port : 1; + unsigned char has_timeout : 1; +}; + +#define OPT_STRING "hm:c:s:n:Ca:p:t:" + +static void usage(const char *prog) +{ + printf("Usage: %s <OPTIONS>\n", prog); + printf("OPTIONS:\n"); + printf(" -h: Show this help and exit. Optional.\n"); + printf(" -m (crash | server_crash | client): Mode. Required.\n"); + printf("Options for crash mode:\n"); + printf(" -c (fork | exec): Crash after. Optional.\n"); + printf(" -s (user | kernel): Signal from. Required.\n"); + printf(" -n counter: Number of crashes.\n"); + printf(" Required if the option -c is used.\n"); + printf(" Not used without the option -c.\n"); + printf(" Range from 1 to INT_MAX.\n"); + printf(" -C: Change privileges before crash. Optional.\n"); + printf("Options for server_crash mode:\n"); + printf(" -a ip: Ip v4 address to accept. Required.\n"); + printf(" -p port: Port number. Required.\n"); + printf(" Range from 1 to UINT16_MAX.\n"); + printf(" -t secs: Accept timeout. Required.\n"); + printf(" Range from 1 to LONG_MAX.\n"); + printf(" -c (fork | exec): Crash after. Required.\n"); + printf(" -s (user | kernel): Signal from. Required.\n"); + printf(" -n counter: Number of crashes. Required.\n"); + printf(" Range from 1 to INT_MAX.\n"); + printf("Options for client mode:\n"); + printf(" -a ip: Ip v4 address to connect. Required.\n"); + printf(" -p port: Port number. Required.\n"); + printf(" Range from 1 to UINT16_MAX.\n"); + printf(" -t secs: Connect timeout. Required.\n"); + printf(" Range from 1 to LONG_MAX.\n"); +} + +static __attribute__((noreturn)) void info_failure(const char *message, + const char *prog) +{ + printf("%s\n", message); + usage(prog); + exit(EXIT_FAILURE); +} + +static enum mode get_mode(const char *text, const char *prog) +{ + if (!strcmp(text, "crash")) + return MODE_CRASH; + + if (!strcmp(text, "server_crash")) + return MODE_SERVER_CRASH; + + if (!strcmp(text, "client")) + return MODE_CLIENT; + + info_failure("Invalid mode option [-m].", prog); +} + +static enum crash_after get_crash_after(const char *text, const char *prog) +{ + if (!strcmp(text, "fork")) + return CRASH_AFTER_FORK; + + if (!strcmp(text, "exec")) + return CRASH_AFTER_EXEC; + + info_failure("Invalid crash after option [-c].", prog); +} + +static enum signal_from get_signal_from(const char *text, const char *prog) +{ + if (!strcmp(text, "user")) + return SIGNAL_FROM_USER; + + if (!strcmp(text, "kernel")) + return SIGNAL_FROM_KERNEL; + + info_failure("Invalid signal from option [-s]", prog); +} + +static int get_counter(const char *text, const char *prog) +{ + int counter; + + counter = atoi(text); + if (counter > 0) + return counter; + + info_failure("Invalid counter option [-n].", prog); +} + +static __attribute__((noreturn)) void error_failure(const char *message) +{ + perror(message); + exit(EXIT_FAILURE); +} + +static uint32_t get_ip(const char *text, const char *prog) +{ + int ret; + uint32_t ip; + + ret = inet_pton(AF_INET, text, &ip); + if (!ret) + info_failure("Invalid ip option [-a].", prog); + else if (ret < 0) + error_failure("inet_pton"); + + return ip; +} + +static uint16_t get_port(const char *text, const char *prog) +{ + long port; + + port = atol(text); + if ((port > 0) && (port <= UINT16_MAX)) + return htons(port); + + info_failure("Invalid port option [-p].", prog); +} + +static long get_timeout(const char *text, const char *prog) +{ + long timeout; + + timeout = atol(text); + if (timeout > 0) + return timeout; + + info_failure("Invalid timeout option [-t].", prog); +} + +static void check_args(const struct args *args, const char *prog) +{ + if (args->mode == MODE_CRASH && args->crash_after != CRASH_AFTER_NONE && + args->signal_from != SIGNAL_FROM_NONE && args->has_counter && + !args->has_ip && !args->has_port && !args->has_timeout) + return; + + if (args->mode == MODE_CRASH && args->signal_from != SIGNAL_FROM_NONE && + args->crash_after == CRASH_AFTER_NONE && !args->has_counter && + !args->has_ip && !args->has_port && !args->has_timeout) + return; + + if (args->mode == MODE_SERVER_CRASH && args->has_ip && args->has_port && + args->has_timeout && args->crash_after != CRASH_AFTER_NONE && + args->signal_from != SIGNAL_FROM_NONE && args->has_counter && + !args->has_change_priv) + return; + + if (args->mode == MODE_CLIENT && args->has_ip && args->has_port && + args->has_timeout && args->crash_after == CRASH_AFTER_NONE && + args->signal_from == SIGNAL_FROM_NONE && !args->has_counter && + !args->has_change_priv) + return; + + info_failure("Invalid use of options.", prog); +} + +static uid_t get_non_root_uid(void) +{ + struct passwd *pwent; + uid_t uid; + + while (true) { + errno = 0; + pwent = getpwent(); + if (!pwent) { + if (errno) { + perror("getpwent"); + endpwent(); + exit(EXIT_FAILURE); + } + break; + } + + if (pwent->pw_uid) { + uid = pwent->pw_uid; + endpwent(); + return uid; + } + } + + endpwent(); + printf("A user different of root is needed.\n"); + exit(EXIT_FAILURE); +} + +static inline void do_sigsegv(void) +{ + int *p = NULL; + *p = 0; +} + +static void do_sigkill(void) +{ + int ret; + + ret = kill(getpid(), SIGKILL); + if (ret) + error_failure("kill"); +} + +static void crash(enum signal_from signal_from, bool change_priv) +{ + int ret; + + if (change_priv) { + ret = setuid(get_non_root_uid()); + if (ret) + error_failure("setuid"); + } + + if (signal_from == SIGNAL_FROM_KERNEL) + do_sigsegv(); + + do_sigkill(); +} + +static void execve_crash(char *const argv[]) +{ + execve(argv[0], argv, NULL); + error_failure("execve"); +} + +static void exec_crash_user(void) +{ + char *const argv[] = { + "./test", "-m", "crash", "-s", "user", NULL, + }; + + execve_crash(argv); +} + +static void exec_crash_user_change_priv(void) +{ + char *const argv[] = { + "./test", "-m", "crash", "-s", "user", "-C", NULL, + }; + + execve_crash(argv); +} + +static void exec_crash_kernel(void) +{ + char *const argv[] = { + "./test", "-m", "crash", "-s", "kernel", NULL, + }; + + execve_crash(argv); +} + +static void exec_crash_kernel_change_priv(void) +{ + char *const argv[] = { + "./test", "-m", "crash", "-s", "kernel", "-C", NULL, + }; + + execve_crash(argv); +} + +static void exec_crash(enum signal_from signal_from, bool change_priv) +{ + if (signal_from == SIGNAL_FROM_USER && !change_priv) + exec_crash_user(); + if (signal_from == SIGNAL_FROM_USER && change_priv) + exec_crash_user_change_priv(); + if (signal_from == SIGNAL_FROM_KERNEL && !change_priv) + exec_crash_kernel(); + if (signal_from == SIGNAL_FROM_KERNEL && change_priv) + exec_crash_kernel_change_priv(); +} + +static void do_crash(enum crash_after crash_after, enum signal_from signal_from, + int counter, bool change_priv) +{ + pid_t pid; + int status; + + if (crash_after == CRASH_AFTER_NONE) + crash(signal_from, change_priv); + + while (counter > 0) { + pid = fork(); + if (pid < 0) + error_failure("fork"); + + /* Child process */ + if (!pid) { + if (crash_after == CRASH_AFTER_FORK) + crash(signal_from, change_priv); + + exec_crash(signal_from, change_priv); + } + + /* Parent process */ + counter -= 1; + pid = waitpid(pid, &status, 0); + if (pid < 0) + error_failure("waitpid"); + } +} + +static __attribute__((noreturn)) void error_close_failure(const char *message, + int fd) +{ + perror(message); + close(fd); + exit(EXIT_FAILURE); +} + +static void do_server(uint32_t ip, uint16_t port, long accept_timeout) +{ + int sockfd; + int ret; + struct sockaddr_in address; + struct timeval timeout; + int newsockfd; + + sockfd = socket(AF_INET, SOCK_STREAM, 0); + if (sockfd < 0) + error_failure("socket"); + + address.sin_family = AF_INET; + address.sin_addr.s_addr = ip; + address.sin_port = port; + + ret = bind(sockfd, (const struct sockaddr *)&address, sizeof(address)); + if (ret) + error_close_failure("bind", sockfd); + + ret = listen(sockfd, 1); + if (ret) + error_close_failure("listen", sockfd); + + timeout.tv_sec = accept_timeout; + timeout.tv_usec = 0; + ret = setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, + (const struct timeval *)&timeout, sizeof(timeout)); + if (ret) + error_close_failure("setsockopt", sockfd); + + newsockfd = accept(sockfd, NULL, NULL); + if (newsockfd < 0) + error_close_failure("accept", sockfd); + + close(sockfd); + close(newsockfd); +} + +static void do_client(uint32_t ip, uint16_t port, long connect_timeout) +{ + int sockfd; + int ret; + struct timeval timeout; + struct sockaddr_in address; + + sockfd = socket(AF_INET, SOCK_STREAM, 0); + if (sockfd < 0) + error_failure("socket"); + + timeout.tv_sec = connect_timeout; + timeout.tv_usec = 0; + ret = setsockopt(sockfd, SOL_SOCKET, SO_SNDTIMEO, + (const struct timeval *)&timeout, sizeof(timeout)); + if (ret) + error_close_failure("setsockopt", sockfd); + + address.sin_family = AF_INET; + address.sin_addr.s_addr = ip; + address.sin_port = port; + + ret = connect(sockfd, (const struct sockaddr *)&address, + sizeof(address)); + if (ret) + error_close_failure("connect", sockfd); + + ret = write(sockfd, message, strlen(message)); + if (ret < 0) + error_close_failure("write", sockfd); + + close(sockfd); +} + +#define PROG_NAME basename(argv[0]) + +int main(int argc, char **argv) +{ + int opt; + struct args args = { + .mode = MODE_NONE, + .crash_after = CRASH_AFTER_NONE, + .signal_from = SIGNAL_FROM_NONE, + .has_counter = false, + .has_change_priv = false, + .has_ip = false, + .has_port = false, + .has_timeout = false, + }; + + while ((opt = getopt(argc, argv, OPT_STRING)) != -1) { + switch (opt) { + case 'h': + usage(PROG_NAME); + return EXIT_SUCCESS; + case 'm': + args.mode = get_mode(optarg, PROG_NAME); + break; + case 'c': + args.crash_after = get_crash_after(optarg, PROG_NAME); + break; + case 's': + args.signal_from = get_signal_from(optarg, PROG_NAME); + break; + case 'n': + args.counter = get_counter(optarg, PROG_NAME); + args.has_counter = true; + break; + case 'C': + args.has_change_priv = true; + break; + case 'a': + args.ip = get_ip(optarg, PROG_NAME); + args.has_ip = true; + break; + case 'p': + args.port = get_port(optarg, PROG_NAME); + args.has_port = true; + break; + case 't': + args.timeout = get_timeout(optarg, PROG_NAME); + args.has_timeout = true; + break; + default: + usage(PROG_NAME); + return EXIT_FAILURE; + } + } + + check_args(&args, PROG_NAME); + + if (args.mode == MODE_CRASH) { + do_crash(args.crash_after, args.signal_from, args.counter, + args.has_change_priv); + } else if (args.mode == MODE_SERVER_CRASH) { + do_server(args.ip, args.port, args.timeout); + do_crash(args.crash_after, args.signal_from, args.counter, + false); + } else if (args.mode == MODE_CLIENT) { + do_client(args.ip, args.port, args.timeout); + } + + return EXIT_SUCCESS; +} diff --git a/tools/testing/selftests/brute/test.sh b/tools/testing/selftests/brute/test.sh new file mode 100755 index 000000000000..47173f38a7c6 --- /dev/null +++ b/tools/testing/selftests/brute/test.sh @@ -0,0 +1,256 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 + +TCID="test.sh" + +KSFT_PASS=0 +KSFT_FAIL=1 +KSFT_SKIP=4 + +errno=$KSFT_PASS + +check_root() +{ + local uid=$(id -u) + if [ $uid -ne 0 ]; then + echo $TCID: must be run as root >&2 + exit $KSFT_SKIP + fi +} + +tmp_files_setup() +{ + DMESG=$(mktemp --tmpdir -t brute-dmesg-XXXXXX) +} + +tmp_files_cleanup() +{ + rm -f "$DMESG" +} + +save_dmesg() +{ + dmesg > "$DMESG" +} + +count_attack_matches() +{ + dmesg | comm --nocheck-order -13 "$DMESG" - | \ + grep "brute: fork brute force attack detected" | wc -l +} + +assert_equal() +{ + local val1=$1 + local val2=$2 + + if [ $val1 -eq $val2 ]; then + echo "$TCID: $message [PASS]" + else + echo "$TCID: $message [FAIL]" + errno=$KSFT_FAIL + fi +} + +test_fork_user() +{ + COUNTER=20 + + save_dmesg + ./test -m crash -c fork -s user -n $COUNTER + count=$(count_attack_matches) + + message="Fork attack (user signals, no bounds crossed)" + assert_equal $count 0 +} + +test_fork_kernel() +{ + save_dmesg + ./test -m crash -c fork -s kernel -n $COUNTER + count=$(count_attack_matches) + + message="Fork attack (kernel signals, no bounds crossed)" + assert_equal $count 0 +} + +test_exec_user() +{ + save_dmesg + ./test -m crash -c exec -s user -n $COUNTER + count=$(count_attack_matches) + + message="Exec attack (user signals, no bounds crossed)" + assert_equal $count 0 +} + +test_exec_kernel() +{ + save_dmesg + ./test -m crash -c exec -s kernel -n $COUNTER + count=$(count_attack_matches) + + message="Exec attack (kernel signals, no bounds crossed)" + assert_equal $count 0 +} + +assert_not_equal() +{ + local val1=$1 + local val2=$2 + + if [ $val1 -ne $val2 ]; then + echo $TCID: $message [PASS] + else + echo $TCID: $message [FAIL] + errno=$KSFT_FAIL + fi +} + +remove_xattr() +{ + ./rmxattr test >/dev/null 2>&1 +} + +test_fork_kernel_setuid() +{ + save_dmesg + chmod u+s test + ./test -m crash -c fork -s kernel -n $COUNTER + chmod u-s test + count=$(count_attack_matches) + + message="Fork attack (kernel signals, setuid binary)" + assert_not_equal $count 0 + remove_xattr +} + +test_exec_kernel_setuid() +{ + save_dmesg + chmod u+s test + ./test -m crash -c exec -s kernel -n $COUNTER + chmod u-s test + count=$(count_attack_matches) + + message="Exec attack (kernel signals, setuid binary)" + assert_not_equal $count 0 + remove_xattr +} + +test_fork_kernel_change_priv() +{ + save_dmesg + ./test -m crash -c fork -s kernel -n $COUNTER -C + count=$(count_attack_matches) + + message="Fork attack (kernel signals, change privileges)" + assert_not_equal $count 0 + remove_xattr +} + +test_exec_kernel_change_priv() +{ + save_dmesg + ./test -m crash -c exec -s kernel -n $COUNTER -C + count=$(count_attack_matches) + + message="Exec attack (kernel signals, change privileges)" + assert_not_equal $count 0 + remove_xattr +} + +network_ns_setup() +{ + local vnet_name=$1 + local veth_name=$2 + local ip_src=$3 + local ip_dst=$4 + + ip netns add $vnet_name + ip link set $veth_name netns $vnet_name + ip -n $vnet_name addr add $ip_src/24 dev $veth_name + ip -n $vnet_name link set $veth_name up + ip -n $vnet_name route add $ip_dst/24 dev $veth_name +} + +network_setup() +{ + VETH0_NAME=veth0 + VNET0_NAME=vnet0 + VNET0_IP=10.0.1.0 + VETH1_NAME=veth1 + VNET1_NAME=vnet1 + VNET1_IP=10.0.2.0 + + ip link add $VETH0_NAME type veth peer name $VETH1_NAME + network_ns_setup $VNET0_NAME $VETH0_NAME $VNET0_IP $VNET1_IP + network_ns_setup $VNET1_NAME $VETH1_NAME $VNET1_IP $VNET0_IP +} + +test_fork_kernel_network_to_local() +{ + INADDR_ANY=0.0.0.0 + PORT=65535 + TIMEOUT=5 + + save_dmesg + ip netns exec $VNET0_NAME ./test -m server_crash -a $INADDR_ANY \ + -p $PORT -t $TIMEOUT -c fork -s kernel -n $COUNTER & + sleep 1 + ip netns exec $VNET1_NAME ./test -m client -a $VNET0_IP -p $PORT \ + -t $TIMEOUT + sleep 1 + count=$(count_attack_matches) + + message="Fork attack (kernel signals, network to local)" + assert_not_equal $count 0 + remove_xattr +} + +test_exec_kernel_network_to_local() +{ + save_dmesg + ip netns exec $VNET0_NAME ./test -m server_crash -a $INADDR_ANY \ + -p $PORT -t $TIMEOUT -c exec -s kernel -n $COUNTER & + sleep 1 + ip netns exec $VNET1_NAME ./test -m client -a $VNET0_IP -p $PORT \ + -t $TIMEOUT + sleep 1 + count=$(count_attack_matches) + + message="Exec attack (kernel signals, network to local)" + assert_not_equal $count 0 + remove_xattr +} + +network_cleanup() +{ + ip netns del $VNET0_NAME >/dev/null 2>&1 + ip netns del $VNET1_NAME >/dev/null 2>&1 + ip link delete $VETH0_NAME >/dev/null 2>&1 + ip link delete $VETH1_NAME >/dev/null 2>&1 +} + +cleanup() +{ + network_cleanup + tmp_files_cleanup + remove_xattr +} +trap cleanup EXIT + +check_root +tmp_files_setup +test_fork_user +test_fork_kernel +test_exec_user +test_exec_kernel +test_fork_kernel_setuid +test_exec_kernel_setuid +test_fork_kernel_change_priv +test_exec_kernel_change_priv +network_setup +test_fork_kernel_network_to_local +test_exec_kernel_network_to_local +exit $errno -- 2.25.1

In order to maintain the code for the Brute LSM add a new entry to the maintainers list.

Signed-off-by: John Wood john.wood@gmx.com --- MAINTAINERS | 7 +++++++ 1 file changed, 7 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS index 008fcad7ac00..102eb3d7dcd6 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -3847,6 +3847,13 @@ L: netdev@vger.kernel.org S: Supported F: drivers/net/ethernet/brocade/bna/

+BRUTE SECURITY MODULE +M: John Wood john.wood@gmx.com +S: Maintained +F: Documentation/admin-guide/LSM/Brute.rst +F: security/brute/ +F: tools/testing/selftests/brute/ + BSG (block layer generic sg v4 driver) M: FUJITA Tomonori fujita.tomonori@lab.ntt.co.jp L: linux-scsi@vger.kernel.org -- 2.25.1