[syzbot] [netfs?] kernel BUG in folio_unlock (3)

[syzbot] [netfs?] kernel BUG in folio_unlock (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    6537cfb395f3 Merge tag 'sound-6.14-rc4' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12af2fdf980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f4f6914bcba459be
dashboard link: https://syzkaller.appspot.com/bug?extid=c0dc46208750f063d0e0
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=165827f8580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=141b4ba4580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-6537cfb3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c6f2faba4c42/vmlinux-6537cfb3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/16fc32b66fc0/bzImage-6537cfb3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c0dc46208750f063d0e0@syzkaller.appspotmail.com

 __vm_munmap+0x19b/0x390 mm/vma.c:2951
 __do_sys_munmap mm/mmap.c:1084 [inline]
 __se_sys_munmap mm/mmap.c:1081 [inline]
 __x64_sys_munmap+0x59/0x80 mm/mmap.c:1081
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
------------[ cut here ]------------
kernel BUG at mm/filemap.c:1499!
Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI
CPU: 3 UID: 0 PID: 5937 Comm: syz-executor137 Not tainted 6.14.0-rc3-syzkaller-00060-g6537cfb395f3 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:folio_unlock mm/filemap.c:1499 [inline]
RIP: 0010:folio_unlock+0xb3/0xd0 mm/filemap.c:1494
Code: f3 68 ca ff 48 89 ef 31 f6 e8 e9 ed ff ff 5b 5d e9 e2 68 ca ff e8 dd 68 ca ff 48 c7 c6 00 8a 78 8b 48 89 ef e8 de c9 11 00 90 <0f> 0b 48 89 df e8 d3 83 2d 00 e9 7b ff ff ff 66 66 2e 0f 1f 84 00
RSP: 0018:ffffc9000359f988 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffc9000359f830
RDX: ffff888027d14880 RSI: ffffffff81ef7612 RDI: ffff888027d14cc4
RBP: ffffea0000dfa680 R08: 0000000000000000 R09: fffffbfff20c49e2
R10: ffffffff90624f17 R11: 0000000000000003 R12: ffff888035b30890
R13: ffff888035b30bb0 R14: ffffea0000dfa680 R15: ffffc9000359fde8
FS:  0000555555b9a380(0000) GS:ffff88806a900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5e877c6264 CR3: 0000000031914000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 netfs_perform_write+0xc04/0x2140 fs/netfs/buffered_write.c:400
 netfs_buffered_write_iter_locked fs/netfs/buffered_write.c:445 [inline]
 netfs_file_write_iter+0x494/0x550 fs/netfs/buffered_write.c:484
 v9fs_file_write_iter+0x9b/0x100 fs/9p/vfs_file.c:407
 new_sync_write fs/read_write.c:586 [inline]
 vfs_write+0x5ae/0x1150 fs/read_write.c:679
 ksys_write+0x12b/0x250 fs/read_write.c:731
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5e87770829
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 a1 1a 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd7fd729d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007ffd7fd729f0 RCX: 00007f5e87770829
RDX: 000000000000000a RSI: 0000400000000080 RDI: 0000000000000004
RBP: 0000000000000001 R08: 00007ffd7fd72777 R09: 00000000000000a0
R10: 0000000000000001 R11: 0000000000000246 R12: 00007ffd7fd729ec
R13: 431bde82d7b634db R14: 0000000000000001 R15: 0000000000000001
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:folio_unlock mm/filemap.c:1499 [inline]
RIP: 0010:folio_unlock+0xb3/0xd0 mm/filemap.c:1494
Code: f3 68 ca ff 48 89 ef 31 f6 e8 e9 ed ff ff 5b 5d e9 e2 68 ca ff e8 dd 68 ca ff 48 c7 c6 00 8a 78 8b 48 89 ef e8 de c9 11 00 90 <0f> 0b 48 89 df e8 d3 83 2d 00 e9 7b ff ff ff 66 66 2e 0f 1f 84 00
RSP: 0018:ffffc9000359f988 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffc9000359f830
RDX: ffff888027d14880 RSI: ffffffff81ef7612 RDI: ffff888027d14cc4
RBP: ffffea0000dfa680 R08: 0000000000000000 R09: fffffbfff20c49e2
R10: ffffffff90624f17 R11: 0000000000000003 R12: ffff888035b30890
R13: ffff888035b30bb0 R14: ffffea0000dfa680 R15: ffffc9000359fde8
FS:  0000555555b9a380(0000) GS:ffff88806a600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005595a83ba0f8 CR3: 0000000031914000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] [netfs?] kernel BUG in folio_unlock (3)

[Matthew Wilcox]

On Thu, Feb 20, 2025 at 08:00:24AM -0800, syzbot wrote:
> ------------[ cut here ]------------
> kernel BUG at mm/filemap.c:1499!

Tried to unlock a folio that wasn't locked.

The entire log is interesting:

https://syzkaller.appspot.com/x/log.txt?x=12af2fdf980000

It injects a failure which hits p9_tag_alloc() (so adding the 9p people
to the cc)

The page dump is:

 page: refcount:1 mapcount:0 mapping:ffff888035b30890 index:0x0 pfn:0x37e9a
 memcg:ffff88801c6be000
 aops:v9fs_addr_operations ino:2721d72 dentry name(?):"file0"
 flags: 0xfff20000000020(lru|node=0|zone=1|lastcpupid=0x7ff)
 raw: 00fff20000000020 ffffea0000e1d1c8 ffff88801b0b31a0 ffff888035b30890
 raw: 0000000000000000 0000000000000000 00000001ffffffff ffff88801c6be000
 page dumped because: VM_BUG_ON_FOLIO(!folio_test_locked(folio))

> Call Trace:
>  <TASK>
>  netfs_perform_write+0xc04/0x2140 fs/netfs/buffered_write.c:400
>  netfs_buffered_write_iter_locked fs/netfs/buffered_write.c:445 [inline]
>  netfs_file_write_iter+0x494/0x550 fs/netfs/buffered_write.c:484
>  v9fs_file_write_iter+0x9b/0x100 fs/9p/vfs_file.c:407
>  new_sync_write fs/read_write.c:586 [inline]
>  vfs_write+0x5ae/0x1150 fs/read_write.c:679
>  ksys_write+0x12b/0x250 fs/read_write.c:731

Re: [syzbot] [netfs?] kernel BUG in folio_unlock (3)

[Dominique Martinet]

Matthew Wilcox wrote on Thu, Feb 20, 2025 at 04:15:53PM +0000:
> On Thu, Feb 20, 2025 at 08:00:24AM -0800, syzbot wrote:
> > ------------[ cut here ]------------
> > kernel BUG at mm/filemap.c:1499!
> 
> Tried to unlock a folio that wasn't locked.
> 
> The entire log is interesting:
> 
> https://syzkaller.appspot.com/x/log.txt?x=12af2fdf980000
> 
> It injects a failure which hits p9_tag_alloc() (so adding the 9p people
> to the cc)

9p is calling iov_iter_revert() in p9_client_write() on failure, but at
this point of the failure copy_from_iter_full (which advanced the iter)
wasn't called yet because the format processing happens after
allocation...

This was changed by Al Viro in 2015 so it's a "fairly old" bug, but it's
a bug on 9p side alright - thanks for the cc

Now to figure out how to decide if we want to revert or not... I
honestly don't have any bright idea, but I don't know the iov API well
at all -- perhaps it's possible to copy without advancing and only
advance the iov if IO worked?

-- 
Dominique Martinet | Asmadeus

Re: [syzbot] [netfs?] kernel BUG in folio_unlock (3)

[Hillf Danton]

On Thu, 20 Feb 2025 08:00:24 -0800
> syzbot found the following issue on:
> 
> HEAD commit:    6537cfb395f3 Merge tag 'sound-6.14-rc4' of git://git.kerne..
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=141b4ba4580000

#syz test

--- x/fs/netfs/buffered_write.c
+++ y/fs/netfs/buffered_write.c
@@ -338,7 +338,7 @@ ssize_t netfs_perform_write(struct kiocb
 		folio_put(folio);
 		ret = filemap_write_and_wait_range(mapping, fpos, fpos + flen - 1);
 		if (ret < 0)
-			goto error_folio_unlock;
+			break;
 		continue;
 
 	copied:
--

Re: [syzbot] [netfs?] kernel BUG in folio_unlock (3)

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+c0dc46208750f063d0e0@syzkaller.appspotmail.com
Tested-by: syzbot+c0dc46208750f063d0e0@syzkaller.appspotmail.com

Tested on:

commit:         ff202c50 Merge tag 'soc-fixes-6.14' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11b30db0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=635cd601ddc51632
dashboard link: https://syzkaller.appspot.com/bug?extid=c0dc46208750f063d0e0
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=16ec3498580000

Note: testing is done by a robot and is best-effort only.

Re: [syzbot] [netfs?] kernel BUG in folio_unlock (3)

[David Howells]

syzbot <syzbot+c0dc46208750f063d0e0@syzkaller.appspotmail.com> wrote:

> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=141b4ba4580000

I'm not sure how this would even work.

  memcpy((void*)0x4000000001c0, "syz\000", 4);
  memcpy((void*)0x400000000480, "./file0\000", 8);
  memcpy((void*)0x4000000004c0, "9p\000", 3);
  memcpy((void*)0x400000000c00,
         "\x56\xc7\x8e\x3c\x73\x3d\x76\x69\x72\x74\x69\x6f\x2c\x6e\x6f\x65\x78"
         "\x74\x65\x6e\x64\x2c\x61\x63\x63\x81\x73\x73\x3d\x61\x6e\x79\x2c\x63"
         "\x61\x63\x68\x65\x3d\x66\x73\x63\x61\x63\x68\x65\x2c\x76\x65\x72\x73"
         "\x69\x6f\x6e\x3d\x39\x70\x32\x30\x30\x30\x2e\x75",
         63);
  syscall(__NR_mount, /*src=*/0x4000000001c0ul, /*dst=*/0x400000000480ul,
          /*type=*/0x4000000004c0ul, /*flags=*/0ul, /*opts=*/0x400000000c00ul);

The options string is rubbish:

[pid  8084] mount("syz", "./file0", "9p", 0, "V\307\216<s=virtio,noextend,acc\201ss=any,cache=fscache,version=9p2000.u") = -1 EINVAL (Invalid argument)

David

Re: [syzbot] [netfs?] kernel BUG in folio_unlock (3)

[syzbot]

syzbot has bisected this issue to:

commit 80f31d2a7e5f4efa7150c951268236c670bcb068
Author: Christoph Hellwig <hch@lst.de>
Date:   Thu May 8 05:14:32 2025 +0000

    f2fs: return bool from __write_node_folio

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1129d00c580000
start commit:   0f70f5b08a47 Merge tag 'pull-automount' of git://git.kerne..
git tree:       upstream
final oops:     https://syzkaller.appspot.com/x/report.txt?x=1329d00c580000
console output: https://syzkaller.appspot.com/x/log.txt?x=1529d00c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=22765942f2e2ebcf
dashboard link: https://syzkaller.appspot.com/bug?extid=c0dc46208750f063d0e0
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15bfe970580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13bfe970580000

Reported-by: syzbot+c0dc46208750f063d0e0@syzkaller.appspotmail.com
Fixes: 80f31d2a7e5f ("f2fs: return bool from __write_node_folio")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [syzbot] [netfs?] kernel BUG in folio_unlock (3)

[Matthew Wilcox]

On Sat, May 31, 2025 at 04:20:02PM -0700, syzbot wrote:
> syzbot has bisected this issue to:
> 
> commit 80f31d2a7e5f4efa7150c951268236c670bcb068
> Author: Christoph Hellwig <hch@lst.de>
> Date:   Thu May 8 05:14:32 2025 +0000

That's not possible; this commit is after the original report.

That said, there _is_ a double folio_unlock() in this patch, which
I'm about to send a fix for.  It's just not fixing the original report.

Re: [syzbot] [netfs?] kernel BUG in folio_unlock (3)

[Aleksandr Nogikh]

On Sun, Jun 1, 2025 at 2:26 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Sat, May 31, 2025 at 04:20:02PM -0700, syzbot wrote:
> > syzbot has bisected this issue to:
> >
> > commit 80f31d2a7e5f4efa7150c951268236c670bcb068
> > Author: Christoph Hellwig <hch@lst.de>
> > Date:   Thu May 8 05:14:32 2025 +0000
>
> That's not possible; this commit is after the original report.
>
> That said, there _is_ a double folio_unlock() in this patch, which
> I'm about to send a fix for.  It's just not fixing the original report.
>

Thanks for bringing this up!
The underlying problem is that syzbot has merged several unrelated
kernel crashes into one bug report (`kernel BUG in folio_unlock` is
just a too generic title). The reported bisection result seems to be
correct, but it refers to only one of those incorrectly merged bugs.

I've just sent a fix for the syzbot's crash report parsing code [1].
It won't affect this specific bug report, but once the new code is
deployed, syzbot will re-report the two underlying findings
separately.

[1] https://github.com/google/syzkaller/pull/6081

-- 
Aleksandr