linux-kernel - Re: [syzbot] [bcachefs?] KASAN: slab-use-after-free Write in bch2_get_next

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Message-ID: <gtbxhrjzbwuevau27w2zi645uu2y4xuhzutebojmh535blvah7@bc4344cq25cs>
Date: Sat, 19 Jul 2025 15:13:18 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: syzbot <syzbot+2b98caf09c41174a9697@...kaller.appspotmail.com>
Cc: linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bcachefs?] KASAN: slab-use-after-free Write in
 bch2_get_next_dev

On Sat, Jul 19, 2025 at 11:47:02AM -0700, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> kernel panic: btree_update_nodes_written leaked btree_trans
> 
> Kernel panic - not syncing: btree_update_nodes_written leaked btree_trans
> CPU: 0 UID: 0 PID: 7134 Comm: syz.4.31 Not tainted 6.16.0-rc6-syzkaller-gcbdeb0ffd5bf #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x99/0x250 lib/dump_stack.c:120
>  panic+0x2db/0x790 kernel/panic.c:382
>  bch2_fs_btree_iter_exit+0x475/0x490 fs/bcachefs/btree_iter.c:3732
>  __bch2_fs_free fs/bcachefs/super.c:640 [inline]
>  bch2_fs_release+0x2ab/0x830 fs/bcachefs/super.c:690
>  kobject_cleanup lib/kobject.c:689 [inline]
>  kobject_release lib/kobject.c:720 [inline]
>  kref_put include/linux/kref.h:65 [inline]
>  kobject_put+0x22b/0x480 lib/kobject.c:737
>  bch2_fs_get_tree+0xb76/0x1540 fs/bcachefs/fs.c:2578
>  vfs_get_tree+0x92/0x2b0 fs/super.c:1804
>  do_new_mount+0x24a/0xa40 fs/namespace.c:3902
>  do_mount fs/namespace.c:4239 [inline]
>  __do_sys_mount fs/namespace.c:4450 [inline]
>  __se_sys_mount+0x317/0x410 fs/namespace.c:4427
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f59aa99014a
> Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f59ab804e68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007f59ab804ef0 RCX: 00007f59aa99014a
> RDX: 00002000000000c0 RSI: 0000200000000080 RDI: 00007f59ab804eb0
> RBP: 00002000000000c0 R08: 00007f59ab804ef0 R09: 0000000000818001
> R10: 0000000000818001 R11: 0000000000000246 R12: 0000200000000080
> R13: 00007f59ab804eb0 R14: 000000000000596b R15: 0000200000000000
>  </TASK>
> Kernel Offset: disabled
> 
> 
> Tested on:
> 
> commit:         cbdeb0ff bcachefs: Fix UAF by journal write path
> git tree:       git://evilpiepirate.org/bcachefs.git for-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1627f8f0580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=37de60b3108b6d8f
> dashboard link: https://syzkaller.appspot.com/bug?extid=2b98caf09c41174a9697
> compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> 
> Note: no patches were applied.

appears we were missing a flush_work() in the shutdown path

#syz test: git://evilpiepirate.org/bcachefs.git bcachefs-testing