[v5.15] UBSAN: shift-out-of-bounds in null_process_zoned_cmd

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6e2fd6534337 Linux 5.15.213
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=17247649580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f161cbc9aef65db0
dashboard link: https://syzkaller.appspot.com/bug?extid=92f93c65f133d6ac44b2
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d7b46606b13d/disk-6e2fd653.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/da120fdeb081/vmlinux-6e2fd653.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3c2643457e3f/bzImage-6e2fd653.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+92f93c...@syzkaller.appspotmail.com

================================================================================
UBSAN: shift-out-of-bounds in drivers/block/null_blk/zoned.c:16:14
shift exponent -1 is negative
CPU: 0 PID: 263 Comm: kworker/0:1H Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: kblockd blk_mq_run_work_fn
Call Trace:
<TASK>
dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
ubsan_epilogue+0xa/0x30 lib/ubsan.c:151
__ubsan_handle_shift_out_of_bounds+0x364/0x3f0 lib/ubsan.c:321
null_zone_no drivers/block/null_blk/zoned.c:16 [inline]
null_process_zoned_cmd+0xf2f/0x1220 drivers/block/null_blk/zoned.c:684
null_handle_cmd+0x362/0x990 drivers/block/null_blk/main.c:1374
blk_mq_dispatch_rq_list+0xa06/0x1c50 block/blk-mq.c:1387
__blk_mq_do_dispatch_sched block/blk-mq-sched.c:200 [inline]
blk_mq_do_dispatch_sched+0xadf/0xc90 block/blk-mq-sched.c:214
__blk_mq_sched_dispatch_requests+0x32c/0x410 block/blk-mq-sched.c:-1
blk_mq_sched_dispatch_requests+0xf4/0x1b0 block/blk-mq-sched.c:366
__blk_mq_run_hw_queue+0xbb/0x100 block/blk-mq.c:1512
process_one_work+0x867/0xff0 kernel/workqueue.c:2310
worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
kthread+0x42e/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>
================================================================================


---
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 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