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fanotify: Disallow permission events for proc filesystem

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Proc filesystem has special locking rules for various files. Thus
fanotify which opens files on event delivery can easily deadlock
against another process that waits for fanotify permission event to be
handled. Since permission events on /proc have doubtful value anyway,
just disallow them.

Link: https://lore.kernel.org/linux-fsdevel/20190320131642.GE9485@quack2.suse.cz/
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Jan Kara 2019-05-15 16:28:34 +02:00
parent cd6c84d8f0
commit 0b3b094ac9
3 changed files with 24 additions and 1 deletions
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22
fs/notify/fanotify/fanotify_user.c
View File

@ -920,6 +920,22 @@ static int fanotify_test_fid(struct path *path, __kernel_fsid_t *fsid)
return 0;
}
static int fanotify_events_supported(struct path *path, __u64 mask)
{
/*
* Some filesystems such as 'proc' acquire unusual locks when opening
* files. For them fanotify permission events have high chances of
* deadlocking the system - open done when reporting fanotify event
* blocks on this "unusual" lock while another process holding the lock
* waits for fanotify permission event to be answered. Just disallow
* permission events for such filesystems.
*/
if (mask & FANOTIFY_PERM_EVENTS &&
path->mnt->mnt_sb->s_type->fs_flags & FS_DISALLOW_NOTIFY_PERM)
return -EINVAL;
return 0;
}
static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
int dfd, const char __user *pathname)
{
@ -1018,6 +1034,12 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
if (ret)
goto fput_and_out;
if (flags & FAN_MARK_ADD) {
ret = fanotify_events_supported(&path, mask);
if (ret)
goto path_put_and_out;
}
if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
ret = fanotify_test_fid(&path, &__fsid);
if (ret)

2
fs/proc/root.c
View File

@ -211,7 +211,7 @@ static struct file_system_type proc_fs_type = {
.init_fs_context = proc_init_fs_context,
.parameters = &proc_fs_parameters,
.kill_sb = proc_kill_sb,
.fs_flags = FS_USERNS_MOUNT,
.fs_flags = FS_USERNS_MOUNT | FS_DISALLOW_NOTIFY_PERM,
};
void __init proc_root_init(void)

1
include/linux/fs.h
View File

@ -2184,6 +2184,7 @@ struct file_system_type {
#define FS_BINARY_MOUNTDATA 2
#define FS_HAS_SUBTYPE 4
#define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */
#define FS_DISALLOW_NOTIFY_PERM 16 /* Disable fanotify permission events */
#define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
int (*init_fs_context)(struct fs_context *);
const struct fs_parameter_description *parameters;