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

From: [email-masked]
Date: Mon, 19 Dec 2022 11:33:29 -0800

On 12/19, Peter Zijlstra wrote:
> On Mon, Dec 19, 2022 at 12:04:43AM -0800, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    13e3c7793e2f Merge tag 'for-netdev' of  
> https://git.kernel...
> > git tree:       bpf
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=177df7e0480000
> > kernel config:   
> https://syzkaller.appspot.com/x/.config?x=b0e91ad4b5f69c47
> > dashboard link:  
> https://syzkaller.appspot.com/bug?extid=b8e8c01c8ade4fe6e48f
> > compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU  
> Binutils for Debian) 2.35.2
> > syz repro:       
> https://syzkaller.appspot.com/x/repro.syz?x=15e87100480000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16ceeb13880000
> >
> > Downloadable assets:
> > disk image:  
> https://storage.googleapis.com/syzbot-assets/373a99daa295/disk-13e3c779.raw.xz
> > vmlinux:  
> https://storage.googleapis.com/syzbot-assets/7fa71ed0fe17/vmlinux-13e3c779.xz
> > kernel image:  
> https://storage.googleapis.com/syzbot-assets/2842ad5c698b/bzImage-13e3c779.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the  
> commit:
> > Reported-by: [email-masked]
> >
> > ==================================================================
> > BUG: KASAN: use-after-free in __lock_acquire+0x3ee7/0x56d0  
> kernel/locking/lockdep.c:4925
> > Read of size 8 at addr ffff8880237d6018 by task syz-executor287/8300
> >
> > CPU: 0 PID: 8300 Comm: syz-executor287 Not tainted  
> 6.1.0-syzkaller-09661-g13e3c7793e2f #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
> Google 10/26/2022
> > Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:88 [inline]
> >  dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106
> >  print_address_description mm/kasan/report.c:284 [inline]
> >  print_report+0x15e/0x45d mm/kasan/report.c:395
> >  kasan_report+0xbf/0x1f0 mm/kasan/report.c:495
> >  __lock_acquire+0x3ee7/0x56d0 kernel/locking/lockdep.c:4925
> >  lock_acquire kernel/locking/lockdep.c:5668 [inline]
> >  lock_acquire+0x1e3/0x630 kernel/locking/lockdep.c:5633
> >  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> >  _raw_spin_lock_irqsave+0x3d/0x60 kernel/locking/spinlock.c:162
> >  put_pmu_ctx kernel/events/core.c:4913 [inline]
> >  put_pmu_ctx+0xad/0x390 kernel/events/core.c:4893
> >  _free_event+0x3c5/0x13d0 kernel/events/core.c:5196
> >  free_event+0x58/0xc0 kernel/events/core.c:5224
> >  __do_sys_perf_event_open+0x66d/0x2980 kernel/events/core.c:12701
> >  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >  do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
> >  entry_SYSCALL_64_after_hwframe+0x63/0xcd

> Does this help?

Let's maybe try it this way:

#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);