On Fri, Oct 11, 2024 at 4:06 AM Lorenzo Stoakes lorenzo.stoakes@oracle.com wrote:
The means by which a pid is determined from a pidfd is duplicated, with some callers holding a reference to the (pid)fd, and others explicitly pinning the pid.
Introduce __pidfd_get_pid() which abstracts both approaches and provide optional output parameters for file->f_flags and the fd (the latter of which, if provided, prevents the function from decrementing the fd's refernce count).
Additionally, allow the ability to open a pidfd by opening a /proc/<pid> directory, utilised by the pidfd_send_signal() system call, providing a pidfd_get_pid_proc() helper function to do so.
Doing this allows us to eliminate open-coded pidfd pid lookup and to consistently handle this in one place.
This lays the groundwork for a subsequent patch which adds a new sentinel pidfd to explicitly reference the current process (i.e. thread group leader) without the need for a pidfd.
Signed-off-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com
include/linux/pid.h | 42 +++++++++++++++++++++++++++++++- kernel/pid.c | 58 ++++++++++++++++++++++++++++++--------------- kernel/signal.c | 22 ++++------------- 3 files changed, 84 insertions(+), 38 deletions(-)
diff --git a/include/linux/pid.h b/include/linux/pid.h index a3aad9b4074c..68b02eab7509 100644 --- a/include/linux/pid.h +++ b/include/linux/pid.h @@ -2,6 +2,7 @@ #ifndef _LINUX_PID_H #define _LINUX_PID_H
+#include <linux/file.h> #include <linux/pid_types.h> #include <linux/rculist.h> #include <linux/rcupdate.h> @@ -72,8 +73,47 @@ extern struct pid init_struct_pid;
struct file;
+/**
- __pidfd_get_pid() - Retrieve a pid associated with the specified pidfd.
- @pidfd: The pidfd whose pid we want, or the fd of a /proc/<pid> file if
@alloc_proc is also set.
- @pin_pid: If set, then the reference counter of the returned pid is
incremented. If not set, then @fd should be provided to pin the
pidfd.
- @allow_proc: If set, then an fd of a /proc/<pid> file can be passed instead
of a pidfd, and this will be used to determine the pid.
- @flags: Output variable, if non-NULL, then the file->f_flags of the
pidfd will be set here.
- @fd: Output variable, if non-NULL, then the pidfd reference will
remain elevated and the caller will need to decrement it
themselves.
- Returns: If successful, the pid associated with the pidfd, otherwise an
error.- */
+struct pid *__pidfd_get_pid(unsigned int pidfd, bool pin_pid,
bool allow_proc, unsigned int *flags,struct fd *fd);+static inline struct pid *pidfd_get_pid(unsigned int pidfd, unsigned int *flags) +{
return __pidfd_get_pid(pidfd, /* pin_pid = */ true,/* allow_proc = */ false,flags, /* fd = */ NULL);+}
+static inline struct pid *pidfd_to_pid_proc(unsigned int pidfd,
unsigned int *flags,struct fd *fd)+{
return __pidfd_get_pid(pidfd, /* pin_pid = */ false,/* allow_proc = */ true,flags, fd);+}
struct pid *pidfd_pid(const struct file *file); -struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags); struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags); int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret); void do_notify_pidfd(struct task_struct *task); diff --git a/kernel/pid.c b/kernel/pid.c index 2715afb77eab..25cc1c36a1b1 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -36,6 +36,7 @@ #include <linux/pid_namespace.h> #include <linux/init_task.h> #include <linux/syscalls.h> +#include <linux/proc_fs.h> #include <linux/proc_ns.h> #include <linux/refcount.h> #include <linux/anon_inodes.h> @@ -534,22 +535,46 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns) } EXPORT_SYMBOL_GPL(find_ge_pid);
-struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags) +struct pid *__pidfd_get_pid(unsigned int pidfd, bool pin_pid,
bool allow_proc, unsigned int *flags,struct fd *fd){
struct fd f;
struct file *file; struct pid *pid;struct fd f = fdget(pidfd);
f = fdget(fd);if (!fd_file(f))
file = fd_file(f);if (!file) return ERR_PTR(-EBADF);
pid = pidfd_pid(fd_file(f));if (!IS_ERR(pid)) {get_pid(pid);*flags = fd_file(f)->f_flags;
pid = pidfd_pid(file);/* If we allow opening a pidfd via /proc/<pid>, do so. */if (IS_ERR(pid) && allow_proc)pid = tgid_pidfd_to_pid(file);if (IS_ERR(pid)) {fdput(f);return pid; }
fdput(f);
if (pin_pid)get_pid(pid);elseWARN_ON_ONCE(!fd); /* Nothing to keep pid/pidfd around? */if (flags)*flags = file->f_flags;/** If the user provides an fd output then it will handle decrementing* its reference counter.*/if (fd)*fd = f;else/* Otherwise we release it. */fdput(f);return pid;}
There is an EXPORT_SYMBOL_GPL(pidfd_get_pid) right after this line. It should also be changed to EXPORT_SYMBOL_GPL(__pidfd_get_pid), otherwise __pidfd_get_pid() will not be exported. A module calling pidfd_get_pid() now inlined in the header file will try to call __pidfd_get_pid() and will have trouble resolving this symbol.
@@ -747,23 +772,18 @@ SYSCALL_DEFINE3(pidfd_getfd, int, pidfd, int, fd, unsigned int, flags) { struct pid *pid;
struct fd f; int ret; /* flags is currently unused - make sure it's unset */ if (flags) return -EINVAL;f = fdget(pidfd);if (!fd_file(f))return -EBADF;pid = pidfd_pid(fd_file(f));
pid = pidfd_get_pid(pidfd, NULL); if (IS_ERR(pid))
ret = PTR_ERR(pid);elseret = pidfd_getfd(pid, fd);
return PTR_ERR(pid);
fdput(f);
ret = pidfd_getfd(pid, fd);put_pid(pid); return ret;} diff --git a/kernel/signal.c b/kernel/signal.c index 4344860ffcac..868bfa674c62 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3875,17 +3875,6 @@ static int copy_siginfo_from_user_any(kernel_siginfo_t *kinfo, return copy_siginfo_from_user(kinfo, info); }
-static struct pid *pidfd_to_pid(const struct file *file) -{
struct pid *pid;pid = pidfd_pid(file);if (!IS_ERR(pid))return pid;return tgid_pidfd_to_pid(file);-}
#define PIDFD_SEND_SIGNAL_FLAGS \ (PIDFD_SIGNAL_THREAD | PIDFD_SIGNAL_THREAD_GROUP | \ PIDFD_SIGNAL_PROCESS_GROUP) @@ -3908,10 +3897,11 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, siginfo_t __user *, info, unsigned int, flags) { int ret;
struct fd f; struct pid *pid; kernel_siginfo_t kinfo; enum pid_type type;
unsigned int f_flags;struct fd f; /* Enforce flags be set to 0 until we add an extension. */ if (flags & ~PIDFD_SEND_SIGNAL_FLAGS)@@ -3921,12 +3911,8 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, if (hweight32(flags & PIDFD_SEND_SIGNAL_FLAGS) > 1) return -EINVAL;
f = fdget(pidfd);if (!fd_file(f))return -EBADF;/* Is this a pidfd? */pid = pidfd_to_pid(fd_file(f));
pid = pidfd_to_pid_proc(pidfd, &f_flags, &f); if (IS_ERR(pid)) { ret = PTR_ERR(pid); goto err;@@ -3939,7 +3925,7 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, switch (flags) { case 0: /* Infer scope from the type of pidfd. */
if (fd_file(f)->f_flags & PIDFD_THREAD)
if (f_flags & PIDFD_THREAD) type = PIDTYPE_PID; else type = PIDTYPE_TGID;-- 2.46.2