general protection fault in ext4_commit_super

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0d52778b Add linux-next specific files for 20201218
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15b4aecb500000
kernel config: https://syzkaller.appspot.com/x/.config?x=5c81cc44aa25b5b3
dashboard link: https://syzkaller.appspot.com/bug?extid=9043030c040ce1849a60
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17983487500000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10c02937500000

The issue was bisected to:

commit e810c942a325cf749e859d7aa3a43dc219cea299
Author: Jan Kara <ja...@suse.cz>
Date: Wed Dec 16 10:18:40 2020 +0000

ext4: save error info to sb through journal if available

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1282f137500000
final oops: https://syzkaller.appspot.com/x/report.txt?x=1182f137500000
console output: https://syzkaller.appspot.com/x/log.txt?x=1682f137500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+904303...@syzkaller.appspotmail.com
Fixes: e810c942a325 ("ext4: save error info to sb through journal if available")

general protection fault, probably for non-canonical address 0xdffffc000000000c: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000060-0x0000000000000067]
CPU: 0 PID: 7 Comm: kworker/0:1 Not tainted 5.10.0-next-20201218-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events flush_stashed_error_work
RIP: 0010:ext4_commit_super+0x52/0x510 fs/ext4/super.c:5548
Code: 48 c1 ea 03 80 3c 02 00 0f 85 21 04 00 00 48 8b 9d 78 06 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 60 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 f1 03 00 00 48 8b 5b 60 48 85 db 0f 84 13 01 00
RSP: 0018:ffffc90000cc7cb8 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 000000000000000c RSI: ffffffff8217a0db RDI: 0000000000000060
RBP: ffff88802441c000 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff8217a7fa R11: 0000000000000000 R12: ffff88802441c000
R13: ffff88802441c678 R14: ffff8880109a5a00 R15: ffff8880b9c34440
FS: 0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000400200 CR3: 0000000014038000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
flush_stashed_error_work+0x1c9/0x2a0 fs/ext4/super.c:727
process_one_work+0x98d/0x1630 kernel/workqueue.c:2275
worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
kthread+0x3b1/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
Modules linked in:
---[ end trace dca7dc492b64f0a6 ]---
RIP: 0010:ext4_commit_super+0x52/0x510 fs/ext4/super.c:5548
Code: 48 c1 ea 03 80 3c 02 00 0f 85 21 04 00 00 48 8b 9d 78 06 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 60 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 f1 03 00 00 48 8b 5b 60 48 85 db 0f 84 13 01 00
RSP: 0018:ffffc90000cc7cb8 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 000000000000000c RSI: ffffffff8217a0db RDI: 0000000000000060
RBP: ffff88802441c000 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff8217a7fa R11: 0000000000000000 R12: ffff88802441c000
R13: ffff88802441c678 R14: ffff8880109a5a00 R15: ffff8880b9c34440
FS: 0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000400200 CR3: 0000000025563000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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[Hillf Danton]

Tue, 22 Dec 2020 00:54:15 -0800

Fix e810c942a325 ("ext4: save error info to sb through journal if available")
by flushing work as part of rollback.

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5171,6 +5171,7 @@ out_fail:
sb->s_fs_info = NULL;
kfree(sbi->s_blockgroup_lock);
out_free_base:
+ flush_work(&sbi->s_error_work);
kfree(sbi);
kfree(orig_data);
fs_put_dax(dax_dev);

[Jan Kara]

Thanks for having a look. I don't think the fix is quite correct though. The
flush_work() should be at failed_mount3: label. So something like attached
fixup. Ted, can you please fold it into the buggy commit?

Honza

> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -5171,6 +5171,7 @@ out_fail:
> sb->s_fs_info = NULL;
> kfree(sbi->s_blockgroup_lock);
> out_free_base:
> + flush_work(&sbi->s_error_work);
> kfree(sbi);
> kfree(orig_data);
> fs_put_dax(dax_dev);

--
Jan Kara <ja...@suse.com>
SUSE Labs, CR

[Theodore Y. Ts'o]

On Tue, Dec 22, 2020 at 12:28:53PM +0100, Jan Kara wrote:
> > Fix e810c942a325 ("ext4: save error info to sb through journal if available")
> > by flushing work as part of rollback.
>
> Thanks for having a look. I don't think the fix is quite correct though. The
> flush_work() should be at failed_mount3: label. So something like attached
> fixup. Ted, can you please fold it into the buggy commit?

Done. I folded it into "ext4: defer saving error info from atomic
context" since this is the commit where we introduced the s_error_work
workqueue.

Thanks!!

- Ted