linux-stable/fs/autofs
Fedor Pchelkin 726deae613 autofs: fix memory leak of waitqueues in autofs_catatonic_mode
[ Upstream commit ccbe77f7e4 ]

Syzkaller reports a memory leak:

BUG: memory leak
unreferenced object 0xffff88810b279e00 (size 96):
  comm "syz-executor399", pid 3631, jiffies 4294964921 (age 23.870s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 08 9e 27 0b 81 88 ff ff  ..........'.....
    08 9e 27 0b 81 88 ff ff 00 00 00 00 00 00 00 00  ..'.............
  backtrace:
    [<ffffffff814cfc90>] kmalloc_trace+0x20/0x90 mm/slab_common.c:1046
    [<ffffffff81bb75ca>] kmalloc include/linux/slab.h:576 [inline]
    [<ffffffff81bb75ca>] autofs_wait+0x3fa/0x9a0 fs/autofs/waitq.c:378
    [<ffffffff81bb88a7>] autofs_do_expire_multi+0xa7/0x3e0 fs/autofs/expire.c:593
    [<ffffffff81bb8c33>] autofs_expire_multi+0x53/0x80 fs/autofs/expire.c:619
    [<ffffffff81bb6972>] autofs_root_ioctl_unlocked+0x322/0x3b0 fs/autofs/root.c:897
    [<ffffffff81bb6a95>] autofs_root_ioctl+0x25/0x30 fs/autofs/root.c:910
    [<ffffffff81602a9c>] vfs_ioctl fs/ioctl.c:51 [inline]
    [<ffffffff81602a9c>] __do_sys_ioctl fs/ioctl.c:870 [inline]
    [<ffffffff81602a9c>] __se_sys_ioctl fs/ioctl.c:856 [inline]
    [<ffffffff81602a9c>] __x64_sys_ioctl+0xfc/0x140 fs/ioctl.c:856
    [<ffffffff84608225>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
    [<ffffffff84608225>] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
    [<ffffffff84800087>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

autofs_wait_queue structs should be freed if their wait_ctr becomes zero.
Otherwise they will be lost.

In this case an AUTOFS_IOC_EXPIRE_MULTI ioctl is done, then a new
waitqueue struct is allocated in autofs_wait(), its initial wait_ctr
equals 2. After that wait_event_killable() is interrupted (it returns
-ERESTARTSYS), so that 'wq->name.name == NULL' condition may be not
satisfied. Actually, this condition can be satisfied when
autofs_wait_release() or autofs_catatonic_mode() is called and, what is
also important, wait_ctr is decremented in those places. Upon the exit of
autofs_wait(), wait_ctr is decremented to 1. Then the unmounting process
begins: kill_sb calls autofs_catatonic_mode(), which should have freed the
waitqueues, but it only decrements its usage counter to zero which is not
a correct behaviour.

edit:imk
This description is of course not correct. The umount performed as a result
of an expire is a umount of a mount that has been automounted, it's not the
autofs mount itself. They happen independently, usually after everything
mounted within the autofs file system has been expired away. If everything
hasn't been expired away the automount daemon can still exit leaving mounts
in place. But expires done in both cases will result in a notification that
calls autofs_wait_release() with a result status. The problem case is the
summary execution of of the automount daemon. In this case any waiting
processes won't be woken up until either they are terminated or the mount
is umounted.
end edit: imk

So in catatonic mode we should free waitqueues which counter becomes zero.

edit: imk
Initially I was concerned that the calling of autofs_wait_release() and
autofs_catatonic_mode() was not mutually exclusive but that can't be the
case (obviously) because the queue entry (or entries) is removed from the
list when either of these two functions are called. Consequently the wait
entry will be freed by only one of these functions or by the woken process
in autofs_wait() depending on the order of the calls.
end edit: imk

Reported-by: syzbot+5e53f70e69ff0c0a1c0c@syzkaller.appspotmail.com
Suggested-by: Takeshi Misawa <jeliantsurux@gmail.com>
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: autofs@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Message-Id: <169112719161.7590.6700123246297365841.stgit@donald.themaw.net>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2023-09-23 11:10:59 +02:00
..
autofs_i.h autofs: remove unused ino field inode 2022-07-17 17:31:42 -07:00
dev-ioctl.c file: Replace ksys_close with close_fd 2020-12-10 12:42:59 -06:00
expire.c autofs: use dentry info count instead of simple_empty() 2022-07-17 17:31:42 -07:00
init.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 83 2019-05-24 17:37:52 +02:00
inode.c autofs: make dentry info count consistent 2022-07-17 17:31:42 -07:00
Kconfig treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Makefile treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
root.c autofs: add comment about autofs_mountpoint_changed() 2022-07-17 17:31:42 -07:00
symlink.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 83 2019-05-24 17:37:52 +02:00
waitq.c autofs: fix memory leak of waitqueues in autofs_catatonic_mode 2023-09-23 11:10:59 +02:00