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

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Date:   Mon, 19 Dec 2022 13:33:36 -0800
From:   sdf@...gle.com
To:     syzbot <syzbot+b8e8c01c8ade4fe6e48f@...kaller.appspotmail.com>
Cc:     acme@...nel.org, alexander.shishkin@...ux.intel.com,
        bpf@...r.kernel.org, jolsa@...nel.org,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        mark.rutland@....com, mingo@...hat.com, namhyung@...nel.org,
        netdev@...r.kernel.org, peterz@...radead.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Read in put_pmu_ctx

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);