Re: [syzbot] KASAN: use-after-free Read in put_pmu_ctx

[sdf@google.com]

On 12/19, syzbot wrote:
> Hello,

> syzbot tried to test the proposed patch but the build/boot failed:

> failed to apply patch:
> checking file kernel/events/core.c
> patch: **** unexpected end of file in patch



> Tested on:

> commit:         13e3c779 Merge tag 'for-netdev' of https://git.kernel...
> git tree:        
> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git
> dashboard link:  
> https://syzkaller.appspot.com/bug?extid=b8e8c01c8ade4fe6e48f
> compiler:
> patch:           
> https://syzkaller.appspot.com/x/patch.diff?x=15861a9f880000


Let's try again with hopefully a better formatted patch..

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git  
13e3c7793e2f

diff --git a/kernel/events/core.c b/kernel/events/core.c
index e47914ac8732..bbff551783e1 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -12689,7 +12689,8 @@ SYSCALL_DEFINE5(perf_event_open,
  	return event_fd;

  err_context:
-	/* event->pmu_ctx freed by free_event() */
+	put_pmu_ctx(event->pmu_ctx);
+	event->pmu_ctx = NULL; /* _free_event() */
  err_locked:
  	mutex_unlock(&ctx->mutex);
  	perf_unpin_context(ctx);