Re: [PATCH 5.10.y] perf: Fix perf_pending_task() UaF

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Apr 08, 2025 at 02:10:44PM +0800, Xiangyu Chen wrote:
> From: Peter Zijlstra <peterz@infradead.org>
> 
> [ Upstream commit 517e6a301f34613bff24a8e35b5455884f2d83d8 ]
> 
> Per syzbot it is possible for perf_pending_task() to run after the
> event is free()'d. There are two related but distinct cases:
> 
>  - the task_work was already queued before destroying the event;
>  - destroying the event itself queues the task_work.
> 
> The first cannot be solved using task_work_cancel() since
> perf_release() itself might be called from a task_work (____fput),
> which means the current->task_works list is already empty and
> task_work_cancel() won't be able to find the perf_pending_task()
> entry.
> 
> The simplest alternative is extending the perf_event lifetime to cover
> the task_work.
> 
> The second is just silly, queueing a task_work while you know the
> event is going away makes no sense and is easily avoided by
> re-arranging how the event is marked STATE_DEAD and ensuring it goes
> through STATE_OFF on the way down.
> 
> Reported-by: syzbot+9228d6098455bb209ec8@syzkaller.appspotmail.com
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Tested-by: Marco Elver <elver@google.com>
> [ Discard the changes in event_sched_out() due to 5.10 don't have the
> commit: 97ba62b27867 ("perf: Add support for SIGTRAP on perf events")
> and commit: ca6c21327c6a ("perf: Fix missing SIGTRAPs") ]
> Signed-off-by: Xiangyu Chen <xiangyu.chen@windriver.com>
> Signed-off-by: He Zhe <zhe.he@windriver.com>
> ---
> Verified the build test.

You missed all of the fix-up patches for this commit that happened after
it, fixing memory leaks and the like.  So if we applied this, we would
have more bugs added to the tree than fixed :(

ALWAYS check for follow-on fixes.

I'll go drop this.

greg k-h