[PATCH] aio: Fix null ptr deref in aio_complete() wakeup

[PATCH] aio: Fix null ptr deref in aio_complete() wakeup

[Kent Overstreet]

list_del_init_careful() needs to be the last access to the wait queue
entry - it effectively unlocks access.

Previously, finish_wait() would see the empty list head and skip taking
the lock, and then we'd return - but the completion path would still
attempt to do the wakeup after the task_struct pointer had been
overwritten.

Fixes: 71eb6b6b0ba9 fs/aio: obey min_nr when doing wakeups
Cc: linux-stable@vger.kernel.org
Link: https://lore.kernel.org/linux-fsdevel/CAHTA-ubfwwB51A5Wg5M6H_rPEQK9pNf8FkAGH=vr=FEkyRrtqw@mail.gmail.com/
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
---
 fs/aio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/aio.c b/fs/aio.c
index 9cdaa2faa536..0f4f531c9780 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1202,8 +1202,8 @@ static void aio_complete(struct aio_kiocb *iocb)
 		spin_lock_irqsave(&ctx->wait.lock, flags);
 		list_for_each_entry_safe(curr, next, &ctx->wait.head, w.entry)
 			if (avail >= curr->min_nr) {
-				list_del_init_careful(&curr->w.entry);
 				wake_up_process(curr->w.private);
+				list_del_init_careful(&curr->w.entry);
 			}
 		spin_unlock_irqrestore(&ctx->wait.lock, flags);
 	}
-- 
2.43.0

Re: [PATCH] aio: Fix null ptr deref in aio_complete() wakeup

[Christian Brauner]

On Sun, 31 Mar 2024 17:52:12 -0400, Kent Overstreet wrote:
> list_del_init_careful() needs to be the last access to the wait queue
> entry - it effectively unlocks access.
> 
> Previously, finish_wait() would see the empty list head and skip taking
> the lock, and then we'd return - but the completion path would still
> attempt to do the wakeup after the task_struct pointer had been
> overwritten.
> 
> [...]

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] aio: Fix null ptr deref in aio_complete() wakeup
      https://git.kernel.org/vfs/vfs/c/4d455e51278f

Re: [PATCH] aio: Fix null ptr deref in aio_complete() wakeup

[Mitchell Augustin]

Thanks for the quick patch!

I just ran my reproducer 50x and did not observe any kernel panics
(either in the ktest environment or on bare metal), so it does seem
that resolves the issue on our end.

-Mitchell Augustin

On Sun, Mar 31, 2024 at 4:52 PM Kent Overstreet
<kent.overstreet@linux.dev> wrote:
>
> list_del_init_careful() needs to be the last access to the wait queue
> entry - it effectively unlocks access.
>
> Previously, finish_wait() would see the empty list head and skip taking
> the lock, and then we'd return - but the completion path would still
> attempt to do the wakeup after the task_struct pointer had been
> overwritten.
>
> Fixes: 71eb6b6b0ba9 fs/aio: obey min_nr when doing wakeups
> Cc: linux-stable@vger.kernel.org
> Link: https://lore.kernel.org/linux-fsdevel/CAHTA-ubfwwB51A5Wg5M6H_rPEQK9pNf8FkAGH=vr=FEkyRrtqw@mail.gmail.com/
> Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
> ---
>  fs/aio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 9cdaa2faa536..0f4f531c9780 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -1202,8 +1202,8 @@ static void aio_complete(struct aio_kiocb *iocb)
>                 spin_lock_irqsave(&ctx->wait.lock, flags);
>                 list_for_each_entry_safe(curr, next, &ctx->wait.head, w.entry)
>                         if (avail >= curr->min_nr) {
> -                               list_del_init_careful(&curr->w.entry);
>                                 wake_up_process(curr->w.private);
> +                               list_del_init_careful(&curr->w.entry);
>                         }
>                 spin_unlock_irqrestore(&ctx->wait.lock, flags);
>         }
> --
> 2.43.0
>