Re: [syzbot] KASAN: null-ptr-deref Read in filp_close (2)

[Christian Brauner]

On Mon, Jul 12, 2021 at 09:12:20PM -0700, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    7fef2edf sd: don't mess with SD_MINORS for CONFIG_DEBUG_BL..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=178919b0300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=20276914ec6ad813
> dashboard link: https://syzkaller.appspot.com/bug?extid=283ce5a46486d6acdbaf
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=120220f2300000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=115f37b4300000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+283ce5a46486d6acdbaf@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ==================================================================
> BUG: KASAN: use-after-free in instrument_atomic_read include/linux/instrumented.h:71 [inline]
> BUG: KASAN: use-after-free in atomic64_read include/asm-generic/atomic-instrumented.h:605 [inline]
> BUG: KASAN: use-after-free in atomic_long_read include/asm-generic/atomic-long.h:29 [inline]
> BUG: KASAN: use-after-free in filp_close+0x22/0x170 fs/open.c:1306
> Read of size 8 at addr ffff888025a40a78 by task syz-executor493/8445

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/ 595fac5cecba71935450ec431eb8dfa963cf45fe