[syzbot] [dm?] WARNING: zero-size vmalloc in cache_ctr

[syzbot <syzbot+c8564fc0a96e3ecbe4d4@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    7a19f0cc94ad Merge branch 'for-next/core' 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=149de721580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6602d83d2f34eb80
dashboard link: https://syzkaller.appspot.com/bug?extid=c8564fc0a96e3ecbe4d4
compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
userspace arch: arm64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16c56469580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1330b721580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/26f2e4202da9/disk-7a19f0cc.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1e23a9081d19/vmlinux-7a19f0cc.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b51f551829ee/Image-7a19f0cc.gz.xz

AI-generated root cause summary:
In drivers/md/dm-cache-target.c, calculate_discard_block_size() doubles
discard_block_size beyond 32 bits when origin_sectors is very large, and calls
sector_div() which truncates the divisor to a 32-bit uint32_t, resulting in
division by zero. On arm64, division by zero architecturally yields 0, setting
discard_nr_blocks to 0 and triggering a zero-size vzalloc() that hits
WARN_ON_ONCE(!size) in __vmalloc_node_range_noprof; the error is subsequently
caught by dm-cache-target and cleanly returned as -ENOMEM. On x86_64, the same
division by zero triggers an unhandled #DE divide error kernel oops.

full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=c8564fc0a96e3ecbe4d4

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c8564fc0a96e3ecbe4d4@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: mm/vmalloc.c:4037 at __vmalloc_node_range_noprof+0xe7c/0xe9c mm/vmalloc.c:-1, CPU#1: syz.0.17/4933
Modules linked in:
CPU: 1 UID: 0 PID: 4933 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2026
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : __vmalloc_node_range_noprof+0xe7c/0xe9c mm/vmalloc.c:-1
lr : __vmalloc_node_range_noprof+0xe78/0xe9c mm/vmalloc.c:4037
sp : ffff800098787520
x29: ffff800098787660 x28: 00e8000000000703 x27: 0000000000000000
x26: 0000000000000000 x25: ffff7000130f0ec0 x24: fffffdffbf800000
x23: 0000000000000000 x22: 00000000ffffffff x21: 0000000000000000
x20: 0000000000000dc0 x19: dfff800000000000 x18: ffff8001237d4000
x17: ffff0001acf92e25 x16: ffff0000ca311d94 x15: 0000000000000009
x14: 00000000006328cc x13: 0000000000000001 x12: 0000000000000000
x11: ffffc1ffbf800000 x10: 000000f000000000 x9 : 0000000000000000
x8 : 0000000000000000 x7 : 00000000ffffffff x6 : 0000000000000000
x5 : 00e8000000000703 x4 : 0000000000000dc0 x3 : ffff800080aa2768
x2 : 0000000000000000 x1 : ffff0000ca311d80 x0 : 0000000000000000
Call trace:
 __vmalloc_node_range_noprof+0xe7c/0xe9c mm/vmalloc.c:-1 (P)
 __vmalloc_node_noprof+0xec/0x14c mm/vmalloc.c:4165
 vzalloc_noprof+0x3c/0x4c mm/vmalloc.c:4243
 alloc_bitset drivers/md/dm-cache-policy-internal.h:126 [inline]
 cache_create drivers/md/dm-cache-target.c:2529 [inline]
 cache_ctr+0x1258/0x1f1c drivers/md/dm-cache-target.c:2649
 dm_table_add_target+0x44c/0xb18 drivers/md/dm-table.c:749
 populate_table drivers/md/dm-ioctl.c:1602 [inline]
 table_load+0x27c/0x764 drivers/md/dm-ioctl.c:1645
 ctl_ioctl drivers/md/dm-ioctl.c:2221 [inline]
 dm_ctl_ioctl+0x884/0xbbc drivers/md/dm-ioctl.c:2243
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __arm64_sys_ioctl+0x154/0x1cc fs/ioctl.c:583
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796
 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606
irq event stamp: 8668
hardirqs last  enabled at (8667): [<ffff800080ade8fc>] seqcount_lockdep_reader_access+0x68/0xcc include/linux/seqlock.h:75
hardirqs last disabled at (8668): [<ffff8000868b91fc>] el1_brk64+0x20/0x54 arch/arm64/kernel/entry-common.c:483
softirqs last  enabled at (8614): [<ffff80008013c764>] local_bh_enable include/linux/bottom_half.h:33 [inline]
softirqs last  enabled at (8614): [<ffff80008013c764>] put_cpu_fpsimd_context arch/arm64/kernel/fpsimd.c:251 [inline]
softirqs last  enabled at (8614): [<ffff80008013c764>] kernel_neon_begin+0x294/0x400 arch/arm64/kernel/fpsimd.c:1924
softirqs last disabled at (8612): [<ffff80008013c5ec>] local_bh_disable include/linux/bottom_half.h:20 [inline]
softirqs last disabled at (8612): [<ffff80008013c5ec>] get_cpu_fpsimd_context arch/arm64/kernel/fpsimd.c:234 [inline]
softirqs last disabled at (8612): [<ffff80008013c5ec>] kernel_neon_begin+0x11c/0x400 arch/arm64/kernel/fpsimd.c:1883
---[ end trace 0000000000000000 ]---
device-mapper: table: 248:0: cache: could not allocate discard bitset (-ENOMEM)
device-mapper: ioctl: error adding target to table


---
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