[v6.1] UBSAN: shift-out-of-bounds in raid5_run

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: fb28aa725e05 Linux 6.1.180
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=147277b9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=872c04466179833f
dashboard link: https://syzkaller.appspot.com/bug?extid=cca5421b805a2520c3f8
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d420eb944682/disk-fb28aa72.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/affae450ab23/vmlinux-fb28aa72.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b9e6919ed519/Image-fb28aa72.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cca542...@syzkaller.appspotmail.com

md/raid:md0: device ram0 operational as raid disk 0
md/raid:md0: raid level 5 active with 1 out of 1 devices, algorithm 0
================================================================================
UBSAN: shift-out-of-bounds in ./include/linux/log2.h:57:13
shift exponent 64 is too large for 64-bit type 'unsigned long'
CPU: 1 PID: 4625 Comm: syz.2.71 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026
Call trace:
dump_backtrace+0x1c4/0x1f0 arch/arm64/kernel/stacktrace.c:158
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
__dump_stack+0x30/0x40 lib/dump_stack.c:88
dump_stack_lvl+0xf4/0x15c lib/dump_stack.c:106
dump_stack+0x1c/0x5c lib/dump_stack.c:113
ubsan_epilogue+0x14/0x48 lib/ubsan.c:151
__ubsan_handle_shift_out_of_bounds+0x2b0/0x348 lib/ubsan.c:321
__roundup_pow_of_two include/linux/log2.h:57 [inline]
raid5_run+0x22dc/0x24c4 drivers/md/raid5.c:8068
md_run+0xe14/0x1de0 drivers/md/md.c:6020
do_md_run+0x4c/0x4a4 drivers/md/md.c:6152
array_state_store+0x5e8/0x944 drivers/md/md.c:-1
md_attr_store+0x168/0x234 drivers/md/md.c:5626
sysfs_kf_write+0x1f8/0x274 fs/sysfs/file.c:140
kernfs_fop_write_iter+0x390/0x4b4 fs/kernfs/file.c:352
call_write_iter include/linux/fs.h:2265 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x3c8/0x7c8 fs/read_write.c:584
ksys_write+0x12c/0x228 fs/read_write.c:637
__do_sys_write fs/read_write.c:649 [inline]
__se_sys_write fs/read_write.c:646 [inline]
__arm64_sys_write+0x7c/0x90 fs/read_write.c:646
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
================================================================================


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: fb28aa725e05 Linux 6.1.180
git tree: linux-6.1.y

console output: https://syzkaller.appspot.com/x/log.txt?x=10ab97b9580000

kernel config: https://syzkaller.appspot.com/x/.config?x=872c04466179833f
dashboard link: https://syzkaller.appspot.com/bug?extid=cca5421b805a2520c3f8
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10738132580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=168b6e49580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d420eb944682/disk-fb28aa72.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/affae450ab23/vmlinux-fb28aa72.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b9e6919ed519/Image-fb28aa72.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cca542...@syzkaller.appspotmail.com

md/raid:md0: device ram0 operational as raid disk 0
md/raid:md0: raid level 5 active with 1 out of 1 devices, algorithm 0
================================================================================
UBSAN: shift-out-of-bounds in ./include/linux/log2.h:57:13
shift exponent 64 is too large for 64-bit type 'unsigned long'

CPU: 1 PID: 4542 Comm: syz.0.19 Not tainted syzkaller #0

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.