[syzbot] BUG: unable to handle kernel NULL pointer dereference in set_page_dirty

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a41a877bc12d Merge branch 'for-next/fixes' into for-kernelci
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=175def47080000
kernel config: https://syzkaller.appspot.com/x/.config?x=5cea15779c42821c
dashboard link: https://syzkaller.appspot.com/bug?extid=775a3440817f74fddb8c
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm64

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+775a34...@syzkaller.appspotmail.com

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
Mem abort info:
ESR = 0x0000000086000005
EC = 0x21: IABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x05: level 1 translation fault
user pgtable: 4k pages, 48-bit VAs, pgdp=00000001249cc000
[0000000000000000] pgd=080000012ee65003, p4d=080000012ee65003, pud=0000000000000000
Internal error: Oops: 86000005 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 3044 Comm: syz-executor.0 Not tainted 6.0.0-rc2-syzkaller-16455-ga41a877bc12d #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/20/2022
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : 0x0
lr : folio_mark_dirty+0xbc/0x208 mm/page-writeback.c:2748
sp : ffff800012803830
x29: ffff800012803830 x28: ffff0000d02c8000 x27: 0000000000000009
x26: 0000000000000001 x25: 0000000000000a00 x24: 0000000000000080
x23: 0000000000000000 x22: ffff0000ef276c00 x21: 05ffc00000000007
x20: ffff0000f14b83b8 x19: fffffc00036409c0 x18: fffffffffffffff5
x17: ffff80000dd7a698 x16: ffff80000dbb8658 x15: 0000000000000000
x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
x11: ff808000083e9814 x10: 0000000000000000 x9 : ffff8000083e9814
x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000
x5 : ffff0000d9028000 x4 : ffff0000d5c31000 x3 : ffff0000d9027f80
x2 : fffffffffffffff0 x1 : fffffc00036409c0 x0 : ffff0000f14b83b8
Call trace:
0x0
set_page_dirty+0x38/0xbc mm/folio-compat.c:62
get_next_nat_page+0x198/0x300 fs/f2fs/node.c:154
__flush_nat_entry_set fs/f2fs/node.c:3005 [inline]
f2fs_flush_nat_entries+0x354/0x988 fs/f2fs/node.c:3109
f2fs_write_checkpoint+0x350/0x568 fs/f2fs/checkpoint.c:1667
f2fs_issue_checkpoint+0x1b0/0x234
f2fs_sync_fs+0x8c/0xc8 fs/f2fs/super.c:1651
sync_filesystem+0xe0/0x134 fs/sync.c:66
generic_shutdown_super+0x38/0x190 fs/super.c:474
kill_block_super+0x30/0x78 fs/super.c:1427
kill_f2fs_super+0x140/0x184 fs/f2fs/super.c:4544
deactivate_locked_super+0x70/0xd4 fs/super.c:332
deactivate_super+0xb8/0xbc fs/super.c:363
cleanup_mnt+0x1f8/0x234 fs/namespace.c:1186
__cleanup_mnt+0x20/0x30 fs/namespace.c:1193
task_work_run+0xc4/0x208 kernel/task_work.c:177
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
do_notify_resume+0x174/0x1d0 arch/arm64/kernel/signal.c:1127
prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
el0_svc+0x9c/0x150 arch/arm64/kernel/entry-common.c:625
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:642
el0t_64_sync+0x18c/0x190
Code: bad PC value
---[ end trace 0000000000000000 ]---


---
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[Andrew Morton]

(cc fsf2 developers)

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: a41a877bc12d Merge branch 'for-next/fixes' into for-kernelci
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci

console output: https://syzkaller.appspot.com/x/log.txt?x=104eb875080000

kernel config: https://syzkaller.appspot.com/x/.config?x=5cea15779c42821c
dashboard link: https://syzkaller.appspot.com/bug?extid=775a3440817f74fddb8c
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm64

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15aebce7080000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=167b5e33080000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+775a34...@syzkaller.appspotmail.com

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
Mem abort info:

ESR = 0x0000000086000004

EC = 0x21: IABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0

FSC = 0x04: level 0 translation fault
user pgtable: 4k pages, 48-bit VAs, pgdp=0000000109ee4000
[0000000000000000] pgd=0000000000000000, p4d=0000000000000000
Internal error: Oops: 86000004 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 3045 Comm: syz-executor330 Not tainted 6.0.0-rc2-syzkaller-16455-ga41a877bc12d #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022

pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : 0x0
lr : folio_mark_dirty+0xbc/0x208 mm/page-writeback.c:2748

sp : ffff800012783970
x29: ffff800012783970 x28: 0000000000000000 x27: ffff800012783b08
x26: 0000000000000001 x25: 0000000000000400 x24: 0000000000000001
x23: ffff0000c736e000 x22: 0000000000000045 x21: 05ffc00000000015
x20: ffff0000ca7403b8 x19: fffffc00032ec600 x18: 0000000000000181
x17: ffff80000c04d6bc x16: ffff80000dbb8658 x15: 0000000000000000

x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
x11: ff808000083e9814 x10: 0000000000000000 x9 : ffff8000083e9814
x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000

x5 : ffff0000cbb19000 x4 : ffff0000cb3d2000 x3 : ffff0000cbb18f80
x2 : fffffffffffffff0 x1 : fffffc00032ec600 x0 : ffff0000ca7403b8

Call trace:
0x0
set_page_dirty+0x38/0xbc mm/folio-compat.c:62

f2fs_update_meta_page+0x80/0xa8 fs/f2fs/segment.c:2369
do_checkpoint+0x794/0xea8 fs/f2fs/checkpoint.c:1522
f2fs_write_checkpoint+0x3b8/0x568 fs/f2fs/checkpoint.c:1679

[Jaegeuk Kim]

2363 void f2fs_update_meta_page(struct f2fs_sb_info *sbi,
2364 void *src, block_t blk_addr)
2365 {
2366 struct page *page = f2fs_grab_meta_page(sbi, blk_addr);

--> f2fs_grab_meta_page() gives a locked page by grab_cache_page().

2367
2368 memcpy(page_address(page), src, PAGE_SIZE);
2369 set_page_dirty(page);
2370 f2fs_put_page(page, 1);
2371 }

Is there a change in folio?

[Matthew Wilcox]

Not directly, but there was a related change, 0af573780b0b which
requires aops->set_page_dirty to be set; is that perhaps missing?
I don't see one in the f2fs_compress_aops, for example.

The other possibiity is that it's a mapping that is missing an ->a_ops.
Is that something f2fs ever does?

I only managed to narrow down the crash to the line:
return mapping->a_ops->dirty_folio(mapping, folio);
so either mapping->a_ops is NULL or mapping->a_ops->dirty_folio is
NULL. The reproducer was on ARM and ARM doesn't emit a 'Code:' line,
unlike x86.

[Jaegeuk Kim]

Do you mean dirty_folio? I think all aops have it except the compressed one
that we don't make it dirty.

>
> The other possibiity is that it's a mapping that is missing an ->a_ops.
> Is that something f2fs ever does?

Hmm, no, I haven't seen this before, and we set aops when mounting the
file system. Ah, if this happens on the corrupted image, yeah, maybe.. I need
to check the error path in f2fs_fill_super.

[Jaegeuk Kim]

Fixed by https://lore.kernel.org/linux-f2fs-devel/20220829215206.3...@kernel.org/T/#u