[syzbot] [block?] general protection fault in bio_alloc_bioset

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8e42d2514a7e Add linux-next specific files for 20260318
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10b35ed6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=1da705b17f2649a3
dashboard link: https://syzkaller.appspot.com/bug?extid=09ddb593eea76a158f42
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1325a06a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/64c940773401/disk-8e42d251.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/aa7a94376665/vmlinux-8e42d251.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5a7ab603c859/bzImage-8e42d251.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+09ddb5...@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 UID: 0 PID: 1116 Comm: kworker/u8:9 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: writeback wb_workfn (flush-8:0)
RIP: 0010:bio_init block/bio.c:214 [inline]
RIP: 0010:bio_init_inline include/linux/bio.h:435 [inline]
RIP: 0010:bio_alloc_bioset+0x664/0xc10 block/bio.c:593
Code: 04 24 00 00 00 00 41 8d 46 ff 0f b7 d8 bf 04 00 00 00 89 de e8 6d b0 3a fd 66 83 fb 04 0f 83 db 00 00 00 4c 89 f8 48 c1 e8 03 <80> 3c 28 00 74 08 4c 89 ff e8 3e 27 a4 fd 49 c7 07 00 00 00 00 49
RSP: 0000:ffffc9000576efe8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff88802998bd00 RSI: 0000000000000000 RDI: 0000000000000004
RBP: dffffc0000000000 R08: ffffffff905435f7 R09: 1ffffffff20a86be
R10: dffffc0000000000 R11: fffffbfff20a86bf R12: 0000000000092800
R13: ffffffff9a8dc840 R14: 0000000000000001 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888124de1000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f51b88511d0 CR3: 0000000072570000 CR4: 00000000003526f0
Call Trace:
<TASK>
bio_alloc include/linux/bio.h:373 [inline]
submit_bh_wbc+0x22d/0x650 fs/buffer.c:2816
__block_write_full_folio+0x810/0xe10 fs/buffer.c:1930
blkdev_writepages+0xef/0x1b0 block/fops.c:486
do_writepages+0x32e/0x550 mm/page-writeback.c:2554
__writeback_single_inode+0x133/0x11a0 fs/fs-writeback.c:1750
writeback_sb_inodes+0x992/0x1a20 fs/fs-writeback.c:2042
__writeback_inodes_wb+0x111/0x240 fs/fs-writeback.c:2118
wb_writeback+0x46a/0xb70 fs/fs-writeback.c:2229
wb_check_start_all fs/fs-writeback.c:2355 [inline]
wb_do_writeback fs/fs-writeback.c:2381 [inline]
wb_workfn+0x95b/0xf50 fs/fs-writeback.c:2414
process_one_work+0x9ab/0x1780 kernel/workqueue.c:3288
process_scheduled_works kernel/workqueue.c:3379 [inline]
worker_thread+0xba8/0x11e0 kernel/workqueue.c:3465
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:bio_init block/bio.c:214 [inline]
RIP: 0010:bio_init_inline include/linux/bio.h:435 [inline]
RIP: 0010:bio_alloc_bioset+0x664/0xc10 block/bio.c:593
Code: 04 24 00 00 00 00 41 8d 46 ff 0f b7 d8 bf 04 00 00 00 89 de e8 6d b0 3a fd 66 83 fb 04 0f 83 db 00 00 00 4c 89 f8 48 c1 e8 03 <80> 3c 28 00 74 08 4c 89 ff e8 3e 27 a4 fd 49 c7 07 00 00 00 00 49
RSP: 0000:ffffc9000576efe8 EFLAGS: 00010246

RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff88802998bd00 RSI: 0000000000000000 RDI: 0000000000000004
RBP: dffffc0000000000 R08: ffffffff905435f7 R09: 1ffffffff20a86be
R10: dffffc0000000000 R11: fffffbfff20a86bf R12: 0000000000092800
R13: ffffffff9a8dc840 R14: 0000000000000001 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888124de1000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000564154e50330 CR3: 000000005d868000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
0: 04 24 add $0x24,%al
2: 00 00 add %al,(%rax)
4: 00 00 add %al,(%rax)
6: 41 8d 46 ff lea -0x1(%r14),%eax
a: 0f b7 d8 movzwl %ax,%ebx
d: bf 04 00 00 00 mov $0x4,%edi
12: 89 de mov %ebx,%esi
14: e8 6d b0 3a fd call 0xfd3ab086
19: 66 83 fb 04 cmp $0x4,%bx
1d: 0f 83 db 00 00 00 jae 0xfe
23: 4c 89 f8 mov %r15,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 80 3c 28 00 cmpb $0x0,(%rax,%rbp,1) <-- trapping instruction
2e: 74 08 je 0x38
30: 4c 89 ff mov %r15,%rdi
33: e8 3e 27 a4 fd call 0xfda42776
38: 49 c7 07 00 00 00 00 movq $0x0,(%r15)
3f: 49 rex.WB


---
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.

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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
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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

[Edward Adam Davis]

#syz test

diff --git a/block/bio.c b/block/bio.c
index 5057047194c4..bbbcd1d2f85d 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -530,11 +530,13 @@ struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
struct bio *bio = NULL;
gfp_t saved_gfp = gfp;
void *p;
+ static DEFINE_MUTEX(bio_alloc_lock);

/* should not use nobvec bioset for nr_vecs > 0 */
if (WARN_ON_ONCE(!mempool_initialized(&bs->bvec_pool) && nr_vecs > 0))
return NULL;

+ mutex_lock(&bio_alloc_lock);
gfp = try_alloc_gfp(gfp);
if (bs->cache && nr_vecs <= BIO_INLINE_VECS) {
/*
@@ -570,8 +572,10 @@ struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
* Give up if we are not allow to sleep as non-blocking mempool
* allocations just go back to the slab allocation.
*/
- if (!(saved_gfp & __GFP_DIRECT_RECLAIM))
+ if (!(saved_gfp & __GFP_DIRECT_RECLAIM)) {
+ mutex_unlock(&bio_alloc_lock);
return NULL;
+ }

punt_bios_to_rescuer(bs);

@@ -594,6 +598,7 @@ struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
else
bio_init(bio, bdev, bvecs, nr_vecs, opf);
bio->bi_pool = bs;
+ mutex_unlock(&bio_alloc_lock);
return bio;
}
EXPORT_SYMBOL(bio_alloc_bioset);

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in bio_alloc_bioset

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]

CPU: 0 UID: 0 PID: 5172 Comm: jbd2/sda1-8 Not tainted syzkaller #0 PREEMPT(full)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026

RIP: 0010:bio_init block/bio.c:214 [inline]
RIP: 0010:bio_init_inline include/linux/bio.h:435 [inline]

RIP: 0010:bio_alloc_bioset+0x67e/0xc30 block/bio.c:597
Code: 04 24 00 00 00 00 41 8d 46 ff 0f b7 d8 bf 04 00 00 00 89 de e8 33 6c 3c fd 66 83 fb 04 0f 83 db 00 00 00 4c 89 f8 48 c1 e8 03 <80> 3c 28 00 74 08 4c 89 ff e8 c4 cf a5 fd 49 c7 07 00 00 00 00 49
RSP: 0018:ffffc9000e6ef7e8 EFLAGS: 00010246

RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000

RDX: ffff88803778bd00 RSI: 0000000000000000 RDI: 0000000000000004
RBP: dffffc0000000000 R08: ffffffff903445f7 R09: 1ffffffff20688be
R10: dffffc0000000000 R11: fffffbfff20688bf R12: 0000000000092800
R13: ffffffff9a6ca840 R14: 0000000000000001 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888124ff3000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007f2f6b59c76f CR3: 000000007cd28000 CR4: 00000000003526f0

Call Trace:
<TASK>
bio_alloc include/linux/bio.h:373 [inline]
submit_bh_wbc+0x22d/0x650 fs/buffer.c:2816

jbd2_journal_commit_transaction+0x2186/0x5ad0 fs/jbd2/commit.c:726
kjournald2+0x3e0/0x760 fs/jbd2/journal.c:201

kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:bio_init block/bio.c:214 [inline]
RIP: 0010:bio_init_inline include/linux/bio.h:435 [inline]

RIP: 0010:bio_alloc_bioset+0x67e/0xc30 block/bio.c:597
Code: 04 24 00 00 00 00 41 8d 46 ff 0f b7 d8 bf 04 00 00 00 89 de e8 33 6c 3c fd 66 83 fb 04 0f 83 db 00 00 00 4c 89 f8 48 c1 e8 03 <80> 3c 28 00 74 08 4c 89 ff e8 c4 cf a5 fd 49 c7 07 00 00 00 00 49
RSP: 0018:ffffc9000e6ef7e8 EFLAGS: 00010246

RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000

RDX: ffff88803778bd00 RSI: 0000000000000000 RDI: 0000000000000004
RBP: dffffc0000000000 R08: ffffffff903445f7 R09: 1ffffffff20688be
R10: dffffc0000000000 R11: fffffbfff20688bf R12: 0000000000092800
R13: ffffffff9a6ca840 R14: 0000000000000001 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888124ff3000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007f2f6b59c76f CR3: 000000007cd28000 CR4: 00000000003526f0

----------------
Code disassembly (best guess):
0: 04 24 add $0x24,%al
2: 00 00 add %al,(%rax)
4: 00 00 add %al,(%rax)
6: 41 8d 46 ff lea -0x1(%r14),%eax
a: 0f b7 d8 movzwl %ax,%ebx
d: bf 04 00 00 00 mov $0x4,%edi
12: 89 de mov %ebx,%esi

14: e8 33 6c 3c fd call 0xfd3c6c4c

19: 66 83 fb 04 cmp $0x4,%bx
1d: 0f 83 db 00 00 00 jae 0xfe
23: 4c 89 f8 mov %r15,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 80 3c 28 00 cmpb $0x0,(%rax,%rbp,1) <-- trapping instruction
2e: 74 08 je 0x38
30: 4c 89 ff mov %r15,%rdi

33: e8 c4 cf a5 fd call 0xfda5cffc

38: 49 c7 07 00 00 00 00 movq $0x0,(%r15)
3f: 49 rex.WB

Tested on:

commit: 785f0eb2 Add linux-next specific files for 20260320
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1646d0ca580000
kernel config: https://syzkaller.appspot.com/x/.config?x=22bf3527036b9be1

dashboard link: https://syzkaller.appspot.com/bug?extid=09ddb593eea76a158f42
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=1177a2f6580000

[Edward Adam Davis]

#syz test

diff --git a/block/bio.c b/block/bio.c

index 5057047194c4..0a870979bd41 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -582,6 +582,9 @@ struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
opf &= ~REQ_ALLOC_CACHE;

p = mempool_alloc(&bs->bio_pool, gfp);
+ if (unlikely(!p))
+ return NULL;
+
bio = p + bs->front_pad;
if (nr_vecs > BIO_INLINE_VECS) {
nr_vecs = BIO_MAX_VECS;

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:

SYZFAIL: failed to recv rpc

SYZFAIL: failed to recv rpc
fd=3 want=4 recv=0 n=0 (errno 9: Bad file descriptor)

Tested on:

commit: 785f0eb2 Add linux-next specific files for 20260320
git tree: linux-next

console output: https://syzkaller.appspot.com/x/log.txt?x=17384d72580000

kernel config: https://syzkaller.appspot.com/x/.config?x=22bf3527036b9be1
dashboard link: https://syzkaller.appspot.com/bug?extid=09ddb593eea76a158f42
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=13e00b52580000

[Edward Adam Davis]

Add a failure check for mempool_alloc() in the slowpath.

[1]

KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]

Workqueue: writeback wb_workfn (flush-8:0)
RIP: 0010:bio_init block/bio.c:214 [inline]
RIP: 0010:bio_init_inline include/linux/bio.h:435 [inline]
RIP: 0010:bio_alloc_bioset+0x664/0xc10 block/bio.c:593

Call Trace:

bio_alloc include/linux/bio.h:373 [inline]
submit_bh_wbc+0x22d/0x650 fs/buffer.c:2816

Fixes: b520c4eef83d ("block: split bio_alloc_bioset more clearly into a fast and slowpath")
Reported-by: syzbot+09ddb5...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=09ddb593eea76a158f42
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
block/bio.c | 3 +++
1 file changed, 3 insertions(+)

--
2.43.0

[Jens Axboe]

Doesn't look right at all. You dropped the backtrace, which shows this is
off __block_write_full_folio() -> submit_bh_wbc() which allocates a bio
from the mempool with GFP_NOIO. That should allow blocking, and hence
mempool_alloc() should NEVER return NULL for that case. If it does,
it's broken, and your change is just papering around that issue.

--
Jens Axboe