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

[Peter Zijlstra <peterz@infradead.org>]

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: syzbot+b8e8c01c8ade4fe6e48f@syzkaller.appspotmail.com
> 
> ==================================================================
> 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?

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);