From: Amir Goldstein amir73il@gmail.com
[ Upstream commit 522249f05c5551aec9ec0ba9b6438f1ec19c138d ]
When working in "fd mode", fanotify_read() needs to open an fd from a dentry to report event->fd to userspace.
Opening an fd from dentry can fail for several reasons. For example, when tasks are gone and we try to open their /proc files or we try to open a WRONLY file like in sysfs or when trying to open a file that was deleted on the remote network server.
Add a new flag FAN_REPORT_FD_ERROR for fanotify_init(). For a group with FAN_REPORT_FD_ERROR, we will send the event with the error instead of the open fd, otherwise userspace may not get the error at all.
For an overflow event, we report -EBADF to avoid confusing FAN_NOFD with -EPERM. Similarly for pidfd open errors we report either -ESRCH or the open error instead of FAN_NOPIDFD and FAN_EPIDFD.
In any case, userspace will not know which file failed to open, so add a debug print for further investigation.
Reported-by: Krishna Vivek Vitta kvitta@microsoft.com Link: https://lore.kernel.org/linux-fsdevel/SI2P153MB07182F3424619EDDD1F393EED46D2... Signed-off-by: Amir Goldstein amir73il@gmail.com Signed-off-by: Jan Kara jack@suse.cz Link: https://patch.msgid.link/20241003142922.111539-1-amir73il@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/notify/fanotify/fanotify_user.c | 85 +++++++++++++++++------------- include/linux/fanotify.h | 1 + include/uapi/linux/fanotify.h | 1 + 3 files changed, 50 insertions(+), 37 deletions(-)
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c index 62fe0b679e586..f4798d613dc22 100644 --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -267,13 +267,6 @@ static int create_fd(struct fsnotify_group *group, const struct path *path, group->fanotify_data.f_flags | __FMODE_NONOTIFY, current_cred()); if (IS_ERR(new_file)) { - /* - * we still send an event even if we can't open the file. this - * can happen when say tasks are gone and we try to open their - * /proc files or we try to open a WRONLY file like in sysfs - * we just send the errno to userspace since there isn't much - * else we can do. - */ put_unused_fd(client_fd); client_fd = PTR_ERR(new_file); } else { @@ -664,7 +657,7 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group, unsigned int info_mode = FAN_GROUP_FLAG(group, FANOTIFY_INFO_MODES); unsigned int pidfd_mode = info_mode & FAN_REPORT_PIDFD; struct file *f = NULL, *pidfd_file = NULL; - int ret, pidfd = FAN_NOPIDFD, fd = FAN_NOFD; + int ret, pidfd = -ESRCH, fd = -EBADF;
pr_debug("%s: group=%p event=%p\n", __func__, group, event);
@@ -692,10 +685,39 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group, if (!FAN_GROUP_FLAG(group, FANOTIFY_UNPRIV) && path && path->mnt && path->dentry) { fd = create_fd(group, path, &f); - if (fd < 0) - return fd; + /* + * Opening an fd from dentry can fail for several reasons. + * For example, when tasks are gone and we try to open their + * /proc files or we try to open a WRONLY file like in sysfs + * or when trying to open a file that was deleted on the + * remote network server. + * + * For a group with FAN_REPORT_FD_ERROR, we will send the + * event with the error instead of the open fd, otherwise + * Userspace may not get the error at all. + * In any case, userspace will not know which file failed to + * open, so add a debug print for further investigation. + */ + if (fd < 0) { + pr_debug("fanotify: create_fd(%pd2) failed err=%d\n", + path->dentry, fd); + if (!FAN_GROUP_FLAG(group, FAN_REPORT_FD_ERROR)) { + /* + * Historically, we've handled EOPENSTALE in a + * special way and silently dropped such + * events. Now we have to keep it to maintain + * backward compatibility... + */ + if (fd == -EOPENSTALE) + fd = 0; + return fd; + } + } } - metadata.fd = fd; + if (FAN_GROUP_FLAG(group, FAN_REPORT_FD_ERROR)) + metadata.fd = fd; + else + metadata.fd = fd >= 0 ? fd : FAN_NOFD;
if (pidfd_mode) { /* @@ -710,18 +732,16 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group, * The PIDTYPE_TGID check for an event->pid is performed * preemptively in an attempt to catch out cases where the event * listener reads events after the event generating process has - * already terminated. Report FAN_NOPIDFD to the event listener - * in those cases, with all other pidfd creation errors being - * reported as FAN_EPIDFD. + * already terminated. Depending on flag FAN_REPORT_FD_ERROR, + * report either -ESRCH or FAN_NOPIDFD to the event listener in + * those cases with all other pidfd creation errors reported as + * the error code itself or as FAN_EPIDFD. */ - if (metadata.pid == 0 || - !pid_has_task(event->pid, PIDTYPE_TGID)) { - pidfd = FAN_NOPIDFD; - } else { + if (metadata.pid && pid_has_task(event->pid, PIDTYPE_TGID)) pidfd = pidfd_prepare(event->pid, 0, &pidfd_file); - if (pidfd < 0) - pidfd = FAN_EPIDFD; - } + + if (!FAN_GROUP_FLAG(group, FAN_REPORT_FD_ERROR) && pidfd < 0) + pidfd = pidfd == -ESRCH ? FAN_NOPIDFD : FAN_EPIDFD; }
ret = -EFAULT; @@ -738,9 +758,6 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group, buf += FAN_EVENT_METADATA_LEN; count -= FAN_EVENT_METADATA_LEN;
- if (fanotify_is_perm_event(event->mask)) - FANOTIFY_PERM(event)->fd = fd; - if (info_mode) { ret = copy_info_records_to_user(event, info, info_mode, pidfd, buf, count); @@ -754,15 +771,18 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group, if (pidfd_file) fd_install(pidfd, pidfd_file);
+ if (fanotify_is_perm_event(event->mask)) + FANOTIFY_PERM(event)->fd = fd; + return metadata.event_len;
out_close_fd: - if (fd != FAN_NOFD) { + if (f) { put_unused_fd(fd); fput(f); }
- if (pidfd >= 0) { + if (pidfd_file) { put_unused_fd(pidfd); fput(pidfd_file); } @@ -829,15 +849,6 @@ static ssize_t fanotify_read(struct file *file, char __user *buf, }
ret = copy_event_to_user(group, event, buf, count); - if (unlikely(ret == -EOPENSTALE)) { - /* - * We cannot report events with stale fd so drop it. - * Setting ret to 0 will continue the event loop and - * do the right thing if there are no more events to - * read (i.e. return bytes read, -EAGAIN or wait). - */ - ret = 0; - }
/* * Permission events get queued to wait for response. Other @@ -846,7 +857,7 @@ static ssize_t fanotify_read(struct file *file, char __user *buf, if (!fanotify_is_perm_event(event->mask)) { fsnotify_destroy_event(group, &event->fse); } else { - if (ret <= 0) { + if (ret <= 0 || FANOTIFY_PERM(event)->fd < 0) { spin_lock(&group->notification_lock); finish_permission_event(group, FANOTIFY_PERM(event), FAN_DENY, NULL); @@ -1932,7 +1943,7 @@ static int __init fanotify_user_setup(void) FANOTIFY_DEFAULT_MAX_USER_MARKS);
BUILD_BUG_ON(FANOTIFY_INIT_FLAGS & FANOTIFY_INTERNAL_GROUP_FLAGS); - BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 12); + BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 13); BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 11);
fanotify_mark_cache = KMEM_CACHE(fsnotify_mark, diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h index 4f1c4f6031180..89ff45bd6f01b 100644 --- a/include/linux/fanotify.h +++ b/include/linux/fanotify.h @@ -36,6 +36,7 @@ #define FANOTIFY_ADMIN_INIT_FLAGS (FANOTIFY_PERM_CLASSES | \ FAN_REPORT_TID | \ FAN_REPORT_PIDFD | \ + FAN_REPORT_FD_ERROR | \ FAN_UNLIMITED_QUEUE | \ FAN_UNLIMITED_MARKS)
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h index cd14c94e9a1e0..2aae6dd706a91 100644 --- a/include/uapi/linux/fanotify.h +++ b/include/uapi/linux/fanotify.h @@ -60,6 +60,7 @@ #define FAN_REPORT_DIR_FID 0x00000400 /* Report unique directory id */ #define FAN_REPORT_NAME 0x00000800 /* Report events with name */ #define FAN_REPORT_TARGET_FID 0x00001000 /* Report dirent target id */ +#define FAN_REPORT_FD_ERROR 0x00002000 /* event->fd can report error */
/* Convenience macro - FAN_REPORT_NAME requires FAN_REPORT_DIR_FID */ #define FAN_REPORT_DFID_NAME (FAN_REPORT_DIR_FID | FAN_REPORT_NAME)