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aio: Fix null ptr deref in aio_complete() wakeup

PATCH Applied Kent Overstreet 4 participants 4 messages Mar 31, 2024 – Apr 1, 2024

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Stable branch VFS Aio
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Kent Overstreet

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#0 lore raw

PATCH 1/1 aio: Fix null ptr deref in aio_complete() wakeup

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 [email protected]
Link https://lore.kernel.org/linux-fsdevel/CAHTA-ubfwwB51A5Wg5M6H_rPEQK9pNf8FkAGH=vr=FEkyRrtqw@mail.gmail.com/ open here
Signed-off-by Kent Overstreet <[email protected]>
---
 fs/aio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
fs/aio.c +1 -1
index 9cdaa2faa536..0f4f531c9780 100644
@@ -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);
 	}
Signature · 1 line
2.43.0
build bot
#1 lore raw
FYI: kernel test robot notices the stable kernel rule is not satisfied.

Hi,

Thanks for your patch.

FYI: kernel test robot notices the stable kernel rule is not satisfied.

The check is based on https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html#option-1

Rule: add the tag "Cc: [email protected]" in the sign-off area to have the patch automatically included in the stable tree.
Subject: [PATCH] aio: Fix null ptr deref in aio_complete() wakeup

Link https://lore.kernel.org/stable/20240331215212.522544-1-kent.overstreet%40linux.dev open here
Signature · 2 lines
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
maintainer Applied
#2 lore raw
In reply to Kent Overstreet
Quoted 9 lines · 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.

[...]

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
#3 lore raw
In reply to Kent Overstreet

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

Quoted 34 lines · 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 [email protected]
Link https://lore.kernel.org/linux-fsdevel/CAHTA-ubfwwB51A5Wg5M6H_rPEQK9pNf8FkAGH=vr=FEkyRrtqw@mail.gmail.com/ open here
Signed-off-by Kent Overstreet <[email protected]>
---
 fs/aio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
fs/aio.c +1 -2
index 9cdaa2faa536..0f4f531c9780 100644
@@ -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