Patch "autofs: fix memory leak of waitqueues in autofs_catatonic_mode" has been added to the 5.10-stable tree

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This is a note to let you know that I've just added the patch titled

    autofs: fix memory leak of waitqueues in autofs_catatonic_mode

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     autofs-fix-memory-leak-of-waitqueues-in-autofs_catat.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 7c16f6e24eaa264c3f497eea2eb2efd07567ab75
Author: Fedor Pchelkin <pchelkin@xxxxxxxxx>
Date:   Fri Aug 4 13:33:12 2023 +0800

    autofs: fix memory leak of waitqueues in autofs_catatonic_mode
    
    [ Upstream commit ccbe77f7e45dfb4420f7f531b650c00c6e9c7507 ]
    
    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@xxxxxxxxxxxxxxxxxxxxxxxxx
    Suggested-by: Takeshi Misawa <jeliantsurux@xxxxxxxxx>
    Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>
    Signed-off-by: Alexey Khoroshilov <khoroshilov@xxxxxxxxx>
    Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
    Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
    Cc: Andrei Vagin <avagin@xxxxxxxxx>
    Cc: autofs@xxxxxxxxxxxxxxx
    Cc: linux-kernel@xxxxxxxxxxxxxxx
    Message-Id: <169112719161.7590.6700123246297365841.stgit@xxxxxxxxxxxxxxxxx>
    Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/autofs/waitq.c b/fs/autofs/waitq.c
index 5ced859dac539..dd479198310e8 100644
--- a/fs/autofs/waitq.c
+++ b/fs/autofs/waitq.c
@@ -32,8 +32,9 @@ void autofs_catatonic_mode(struct autofs_sb_info *sbi)
 		wq->status = -ENOENT; /* Magic is gone - report failure */
 		kfree(wq->name.name);
 		wq->name.name = NULL;
-		wq->wait_ctr--;
 		wake_up_interruptible(&wq->queue);
+		if (!--wq->wait_ctr)
+			kfree(wq);
 		wq = nwq;
 	}
 	fput(sbi->pipe);	/* Close the pipe */



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