Re: [syzbot] KFENCE: use-after-free in kmem_cache_destroy

[Chao Yu]

Hi Macro,

I've figured out a patch for this issue.

https://git.kernel.org/pub/scm/linux/kernel/git/chao/linux.git/commit/?h=dev&id=cad83c968c2ebe97905f900326988ed37146c347

Thanks,

On 2021/5/18 19:14, Marco Elver wrote:
> +Cc more people who recently touched f2fs
>
> On Mon, 3 May 2021 at 10:27, 'Dmitry Vyukov' via syzkaller-bugs
> <syzkaller-bugs@xxxxxxxxxxxxxxxx> wrote:
> > On Mon, May 3, 2021 at 10:24 AM syzbot <syzbot+9d90dad32dd9727ed084@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit:    d2b6f8a1 Merge tag 'xfs-5.13-merge-3' of git://git.kernel...
> > > git tree:       upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=15f19ca5d00000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=53fdf14defd48c56
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=9d90dad32dd9727ed084
> > > compiler:       Debian clang version 11.0.1-2
> > >
> > > Unfortunately, I don't have any reproducer for this issue yet.
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+9d90dad32dd9727ed084@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > This looks like a bug in F2FS.
> > Interestingly this was detected by ARM MTE before but was
> > mis-root-caused I think:
> > https://lore.kernel.org/lkml/0000000000008d396205b9e4adee@xxxxxxxxxx/
> > This can't be detected by KASAN directly because it doesn't instrument
> > mm/slab*. This can only be detected by MTE/KFENCE.
> >
> > > ==================================================================
> > > BUG: KFENCE: use-after-free write in kmem_cache_destroy+0x1f/0x120 mm/slab_common.c:486
> > >
> > > Use-after-free write at 0xffff88823bc16040 (in kfence-#10):
> > >   kmem_cache_destroy+0x1f/0x120 mm/slab_common.c:486
> > >   f2fs_recover_fsync_data+0x75b0/0x8380 fs/f2fs/recovery.c:869
>
> This looks like a double-kmem_cache_destroy of fsync_entry_slab in the
> f2fs code. But looking at this code briefly, I couldn't say what the
> fix would be.
>
> > >   f2fs_fill_super+0x9393/0xa420 fs/f2fs/super.c:3945
> > >   mount_bdev+0x26c/0x3a0 fs/super.c:1367
> > >   legacy_get_tree+0xea/0x180 fs/fs_context.c:592
> > >   vfs_get_tree+0x86/0x270 fs/super.c:1497
> > >   do_new_mount fs/namespace.c:2905 [inline]
> > >   path_mount+0x196f/0x2be0 fs/namespace.c:3235
> > >   do_mount fs/namespace.c:3248 [inline]
> > >   __do_sys_mount fs/namespace.c:3456 [inline]
> > >   __se_sys_mount+0x2f9/0x3b0 fs/namespace.c:3433
> > >   do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
> > >   entry_SYSCALL_64_after_hwframe+0x44/0xae
> > >
> > > kfence-#10 [0xffff88823bc16000-0xffff88823bc160df, size=224, cache=kmem_cache] allocated by task 15453:
> > >   kmem_cache_zalloc include/linux/slab.h:676 [inline]
> > >   create_cache mm/slab_common.c:247 [inline]
> > >   kmem_cache_create_usercopy+0x12a/0x2f0 mm/slab_common.c:350
> > >   kmem_cache_create+0xf/0x20 mm/slab_common.c:405
> > >   f2fs_kmem_cache_create fs/f2fs/f2fs.h:2463 [inline]
> > >   f2fs_recover_fsync_data+0x1f0/0x8380 fs/f2fs/recovery.c:790
> > >   f2fs_fill_super+0x9393/0xa420 fs/f2fs/super.c:3945
> > >   mount_bdev+0x26c/0x3a0 fs/super.c:1367
> > >   legacy_get_tree+0xea/0x180 fs/fs_context.c:592
> > >   vfs_get_tree+0x86/0x270 fs/super.c:1497
> > >   do_new_mount fs/namespace.c:2905 [inline]
> > >   path_mount+0x196f/0x2be0 fs/namespace.c:3235
> > >   do_mount fs/namespace.c:3248 [inline]
> > >   __do_sys_mount fs/namespace.c:3456 [inline]
> > >   __se_sys_mount+0x2f9/0x3b0 fs/namespace.c:3433
> > >   do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
> > >   entry_SYSCALL_64_after_hwframe+0x44/0xae
> > >
> > > freed by task 15448:
> > >   kobject_cleanup+0x1c9/0x280 lib/kobject.c:705
> > >   shutdown_cache mm/slab_common.c:463 [inline]
> > >   kmem_cache_destroy+0x93/0x120 mm/slab_common.c:492
> > >   f2fs_recover_fsync_data+0x75b0/0x8380 fs/f2fs/recovery.c:869
> > >   f2fs_fill_super+0x9393/0xa420 fs/f2fs/super.c:3945
> > >   mount_bdev+0x26c/0x3a0 fs/super.c:1367
> > >   legacy_get_tree+0xea/0x180 fs/fs_context.c:592
> > >   vfs_get_tree+0x86/0x270 fs/super.c:1497
> > >   do_new_mount fs/namespace.c:2905 [inline]
> > >   path_mount+0x196f/0x2be0 fs/namespace.c:3235
> > >   do_mount fs/namespace.c:3248 [inline]
> > >   __do_sys_mount fs/namespace.c:3456 [inline]
> > >   __se_sys_mount+0x2f9/0x3b0 fs/namespace.c:3433
> > >   do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
> > >   entry_SYSCALL_64_after_hwframe+0x44/0xae
> > >
> > > CPU: 0 PID: 15453 Comm: syz-executor.0 Not tainted 5.12.0-syzkaller #0
> > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > > RIP: 0010:kmem_cache_destroy+0x1f/0x120 mm/slab_common.c:488
> > > Code: 0f 1f 84 00 00 00 00 00 0f 1f 00 48 85 ff 0f 84 09 01 00 00 41 57 41 56 53 48 89 fb 48 c7 c7 b8 07 dc 8c 31 f6 e8 b1 c3 00 08 <ff> 4b 40 0f 85 c0 00 00 00 48 89 df e8 20 a2 14 00 48 89 df e8 18
> > > RSP: 0018:ffffc900030af320 EFLAGS: 00010286
> > > RAX: 0000000000000000 RBX: ffff88823bc16000 RCX: 0000000000000001
> > > RDX: 0000000000000001 RSI: 0000000000000008 RDI: 0000000000000001
> > > RBP: ffffc900030af870 R08: dffffc0000000000 R09: fffffbfff19b80f8
> > > R10: fffffbfff19b80f8 R11: 0000000000000000 R12: ffff88808c3a4000
> > > R13: dffffc0000000000 R14: 0000000000000000 R15: 1ffff92000615eb0
> > > FS:  00007f60a5228700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
> > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > CR2: ffff88823bc16040 CR3: 000000001ccd8000 CR4: 00000000001526f0
> > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > Call Trace:
> > >   f2fs_recover_fsync_data+0x75b0/0x8380 fs/f2fs/recovery.c:869
> > >   f2fs_fill_super+0x9393/0xa420 fs/f2fs/super.c:3945
> > >   mount_bdev+0x26c/0x3a0 fs/super.c:1367
> > >   legacy_get_tree+0xea/0x180 fs/fs_context.c:592
> > >   vfs_get_tree+0x86/0x270 fs/super.c:1497
> > >   do_new_mount fs/namespace.c:2905 [inline]
> > >   path_mount+0x196f/0x2be0 fs/namespace.c:3235
> > >   do_mount fs/namespace.c:3248 [inline]
> > >   __do_sys_mount fs/namespace.c:3456 [inline]
> > >   __se_sys_mount+0x2f9/0x3b0 fs/namespace.c:3433
> > >   do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
> > >   entry_SYSCALL_64_after_hwframe+0x44/0xae
> > > RIP: 0033:0x467b1a
> > > Code: 48 c7 c2 bc ff ff ff f7 d8 64 89 02 b8 ff ff ff ff eb d2 e8 b8 04 00 00 0f 1f 84 00 00 00 00 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
> > > RSP: 002b:00007f60a5227fa8 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
> > > RAX: ffffffffffffffda RBX: 0000000020000200 RCX: 0000000000467b1a
> > > RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007f60a5228000
> > > RBP: 00007f60a5228040 R08: 00007f60a5228040 R09: 0000000020000000
> > > R10: 0000000000000000 R11: 0000000000000206 R12: 0000000020000000
> > > R13: 0000000020000100 R14: 00007f60a5228000 R15: 0000000020014b00
> > > ==================================================================
> > >
> > >
> > > ---
> > > This report is generated by a bot. It may contain errors.
> > > See https://goo.gl/tpsmEJ for more information about syzbot.
> > > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
> > >
> > > syzbot will keep track of this issue. See:
> > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.