[syzbot] [block?] BUG: unable to handle kernel NULL pointer dereference in __bio_release_pages

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 052d534373b7 Merge tag 'exfat-for-6.8-rc1' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17957913e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=9603f9823d535d97
dashboard link: https://syzkaller.appspot.com/bug?extid=004c1e0fced2b4bc3dcc
compiler: aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13529733e80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=166850dde80000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/384ffdcca292/non_bootable_disk-052d5343.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/74cc52d4cc15/vmlinux-052d5343.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a2da7e6a234c/Image-052d5343.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+004c1e...@syzkaller.appspotmail.com

Unable to handle kernel paging request at virtual address dfff800000000001
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
Mem abort info:
ESR = 0x0000000096000005
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x05: level 1 translation fault
Data abort info:
ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
CM = 0, WnR = 0, TnD = 0, TagAccess = 0
GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[dfff800000000001] address between user and kernel address ranges
Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 3139 Comm: syz-executor303 Not tainted 6.7.0-syzkaller-09928-g052d534373b7 #0
Hardware name: linux,dummy-virt (DT)
pstate: 10000005 (nzcV daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : _compound_head include/linux/page-flags.h:247 [inline]
pc : bio_first_folio include/linux/bio.h:289 [inline]
pc : __bio_release_pages+0x100/0x73c block/bio.c:1153
lr : bio_release_pages include/linux/bio.h:508 [inline]
lr : blkdev_bio_end_io+0x2a0/0x3f0 block/fops.c:157
sp : ffff800089a375e0
x29: ffff800089a375e0 x28: 1fffe0000162e879 x27: ffff00000b1743c0
x26: ffff00000b1743c8 x25: 000000000000000a x24: 1fffe000015a9e12
x23: ffff00000ad4f094 x22: ffff00000f496600 x21: 1fffe0000162e87a
x20: 0000000000000004 x19: 0000000000000000 x18: ffff00000b174432
x17: ffff00000b174438 x16: ffff00000f948008 x15: 1fffe0000162e886
x14: ffff00000b1743d4 x13: 00000000f1f1f1f1 x12: ffff6000015a9e13
x11: 1fffe000015a9e12 x10: ffff6000015a9e12 x9 : dfff800000000000
x8 : ffff00000b1743d4 x7 : 0000000041b58ab3 x6 : 1ffff00011346ed0
x5 : ffff700011346ed0 x4 : 00000000f1f1f1f1 x3 : 000000000000f1f1
x2 : 0000000000000001 x1 : dfff800000000000 x0 : 0000000000000008
Call trace:
_compound_head include/linux/page-flags.h:247 [inline]
bio_first_folio include/linux/bio.h:289 [inline]
__bio_release_pages+0x100/0x73c block/bio.c:1153
bio_release_pages include/linux/bio.h:508 [inline]
blkdev_bio_end_io+0x2a0/0x3f0 block/fops.c:157
bio_endio+0x4a4/0x618 block/bio.c:1608
__blkdev_direct_IO block/fops.c:213 [inline]
blkdev_direct_IO.part.0+0xf08/0x13c0 block/fops.c:379
blkdev_direct_IO block/fops.c:370 [inline]
blkdev_direct_write block/fops.c:648 [inline]
blkdev_write_iter+0x430/0x91c block/fops.c:706
call_write_iter include/linux/fs.h:2085 [inline]
do_iter_readv_writev+0x194/0x298 fs/read_write.c:741
vfs_writev+0x244/0x684 fs/read_write.c:971
do_pwritev+0x15c/0x1e0 fs/read_write.c:1072
__do_sys_pwritev2 fs/read_write.c:1131 [inline]
__se_sys_pwritev2 fs/read_write.c:1122 [inline]
__arm64_sys_pwritev2+0xac/0x120 fs/read_write.c:1122
__invoke_syscall arch/arm64/kernel/syscall.c:37 [inline]
invoke_syscall+0x6c/0x258 arch/arm64/kernel/syscall.c:51
el0_svc_common.constprop.0+0xac/0x230 arch/arm64/kernel/syscall.c:136
do_el0_svc+0x40/0x58 arch/arm64/kernel/syscall.c:155
el0_svc+0x58/0x140 arch/arm64/kernel/entry-common.c:678
el0t_64_sync_handler+0x100/0x12c arch/arm64/kernel/entry-common.c:696
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:595
Code: d2d00001 f2fbffe1 91002260 d343fc02 (38e16841)
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
0: d2d00001 mov x1, #0x800000000000 // #140737488355328
4: f2fbffe1 movk x1, #0xdfff, lsl #48
8: 91002260 add x0, x19, #0x8
c: d343fc02 lsr x2, x0, #3
* 10: 38e16841 ldrsb w1, [x2, x1] <-- trapping instruction


---
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 syzk...@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

[Jens Axboe]

This looks to be caused by:

commit 1b151e2435fc3a9b10c8946c6aebe9f3e1938c55
Author: Matthew Wilcox (Oracle) <wi...@infradead.org>
Date: Mon Aug 14 15:41:00 2023 +0100

block: Remove special-casing of compound pages

--
Jens Axboe

[Jens Axboe]

I suspect this should fix it.

diff --git a/block/bio.c b/block/bio.c
index b9642a41f286..d271f093abb9 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1150,6 +1150,12 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
{
struct folio_iter fi;

+ /*
+ * No pages, nothing to do
+ */
+ if (!bio->bi_vcnt)
+ return;
+
bio_for_each_folio_all(fi, bio) {
struct page *page;
size_t done = 0;

--
Jens Axboe

[Matthew Wilcox]

> This looks to be caused by:
>
> commit 1b151e2435fc3a9b10c8946c6aebe9f3e1938c55
> Author: Matthew Wilcox (Oracle) <wi...@infradead.org>
> Date: Mon Aug 14 15:41:00 2023 +0100
>
> block: Remove special-casing of compound pages

This looks familiar ... looks like it came up right before Xmas and
I probably dropped the patch on the floor?

https://lore.kernel.org/all/ZX07SsSq...@casper.infradead.org/

diff --git a/include/linux/bio.h b/include/linux/bio.h
index ec4db73e5f4e..1518f1201ddd 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -286,6 +286,11 @@ static inline void bio_first_folio(struct folio_iter *fi, struct bio *bio,
{
struct bio_vec *bvec = bio_first_bvec_all(bio) + i;

+ if (i >= bio->bi_vcnt) {
+ fi->folio = NULL;
+ return;
+ }
+
fi->folio = page_folio(bvec->bv_page);
fi->offset = bvec->bv_offset +
PAGE_SIZE * (bvec->bv_page - &fi->folio->page);
@@ -303,10 +308,8 @@ static inline void bio_next_folio(struct folio_iter *fi, struct bio *bio)
fi->offset = 0;
fi->length = min(folio_size(fi->folio), fi->_seg_count);
fi->_next = folio_next(fi->folio);
- } else if (fi->_i + 1 < bio->bi_vcnt) {
- bio_first_folio(fi, bio, fi->_i + 1);
} else {
- fi->folio = NULL;
+ bio_first_folio(fi, bio, fi->_i + 1);
}
}

[Jens Axboe]

Can you send out a proper patch please?


--
Jens Axboe