[v6.1] KASAN: use-after-free Read in _find_next_zero_bit

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 28c695c365e1 Linux 6.1.150
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=15246962580000
kernel config: https://syzkaller.appspot.com/x/.config?x=68aa5a3af1cb953a
dashboard link: https://syzkaller.appspot.com/bug?extid=80597d1d598a86e89519
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/16e807247bf6/disk-28c695c3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a2c735eaf8f9/vmlinux-28c695c3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/080f0096d6c9/Image-28c695c3.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+80597d...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in _find_next_zero_bit+0xc4/0x12c lib/find_bit.c:180
Read of size 8 at addr ffff0000fccd5000 by task syz.3.202/5921

CPU: 1 PID: 5921 Comm: syz.3.202 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
Call trace:
dump_backtrace+0x1c8/0x1f4 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+0xf8/0x160 lib/dump_stack.c:106
print_address_description+0x88/0x218 mm/kasan/report.c:316
print_report+0x50/0x68 mm/kasan/report.c:420
kasan_report+0xa8/0x100 mm/kasan/report.c:524
__asan_report_load8_noabort+0x2c/0x38 mm/kasan/report_generic.c:351
_find_next_zero_bit+0xc4/0x12c lib/find_bit.c:180
find_next_zero_bit include/linux/find.h:151 [inline]
find_next_zero_bit_le include/linux/find.h:420 [inline]
bitmap_search_next_usable_block fs/ext2/balloc.c:590 [inline]
alloc_new_reservation fs/ext2/balloc.c:972 [inline]
ext2_try_to_allocate_with_rsv+0xb48/0x1234 fs/ext2/balloc.c:1124
ext2_new_blocks+0x614/0x1200 fs/ext2/balloc.c:1309
ext2_alloc_blocks fs/ext2/inode.c:418 [inline]
ext2_alloc_branch fs/ext2/inode.c:487 [inline]
ext2_get_blocks+0xb00/0x1afc fs/ext2/inode.c:730
ext2_get_block+0xc8/0x3f4 fs/ext2/inode.c:787
__block_write_begin_int+0x34c/0x13b8 fs/buffer.c:1991
__block_write_begin fs/buffer.c:2041 [inline]
block_write_begin+0x98/0x11c fs/buffer.c:2102
ext2_write_begin+0x44/0x88 fs/ext2/inode.c:903
generic_perform_write+0x230/0x4b0 mm/filemap.c:3846
__generic_file_write_iter+0x168/0x37c mm/filemap.c:3974
generic_file_write_iter+0xb4/0x2b0 mm/filemap.c:4006
ext2_file_write_iter+0xc4/0x404 fs/ext2/file.c:179
call_write_iter include/linux/fs.h:2265 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x5ac/0x7c4 fs/read_write.c:584
ksys_write+0x120/0x210 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+0x98/0x2bc arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x138 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

The buggy address belongs to the physical page:
page:00000000efae5ca0 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x13ccd5
flags: 0x5ffc00000000000(node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000000000 fffffc0003f2db88 fffffc0003e5f388 0000000000000000
raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff0000fccd4f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff0000fccd4f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff0000fccd5000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff0000fccd5080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff0000fccd5100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


---
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

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 28c695c365e1 Linux 6.1.150
git tree: linux-6.1.y

console output: https://syzkaller.appspot.com/x/log.txt?x=16c49134580000

kernel config: https://syzkaller.appspot.com/x/.config?x=68aa5a3af1cb953a
dashboard link: https://syzkaller.appspot.com/bug?extid=80597d1d598a86e89519
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17403312580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=153cd962580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/16e807247bf6/disk-28c695c3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a2c735eaf8f9/vmlinux-28c695c3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/080f0096d6c9/Image-28c695c3.gz.xz

mounted in repro #1: https://storage.googleapis.com/syzbot-assets/61f0ffb2e8f1/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=113cd962580000)
mounted in repro #2: https://storage.googleapis.com/syzbot-assets/f246ccd872c1/mount_5.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=12c49134580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+80597d...@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 512
EXT2-fs (loop0): nobh option not supported
EXT2-fs (loop0): warning: mounting ext3 filesystem as ext2

==================================================================
BUG: KASAN: use-after-free in _find_next_zero_bit+0xc4/0x12c lib/find_bit.c:180

Read of size 8 at addr ffff0000e960a000 by task syz.0.24/4514

CPU: 0 PID: 4514 Comm: syz.0.24 Not tainted syzkaller #0

page:000000006401c3cd refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x12960a
flags: 0x5ffc00000000000(node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000000000 fffffc0003a5f8c8 fffffc0003a37788 0000000000000000

raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:

ffff0000e9609f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff0000e9609f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff0000e960a000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff0000e960a080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff0000e960a100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


---
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.