[moderation] [mm?] KASAN: use-after-free Read in copy_folio_from_iter_atomic (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8f0b4cce4481 Linux 6.19-rc1
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=13bbabb4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8a8594efdc14f07a
dashboard link: https://syzkaller.appspot.com/bug?extid=635d2e8b941d3f241b24
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64
CC: [ak...@linux-foundation.org baoli...@linux.alibaba.com hu...@google.com linux-...@vger.kernel.org linu...@kvack.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cd4f5f43efc8/disk-8f0b4cce.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/aafb35ac3a3c/vmlinux-8f0b4cce.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d221fae4ab17/Image-8f0b4cce.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+635d2e...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in memcpy_from_iter lib/iov_iter.c:85 [inline]
BUG: KASAN: use-after-free in iterate_bvec include/linux/iov_iter.h:123 [inline]
BUG: KASAN: use-after-free in iterate_and_advance2 include/linux/iov_iter.h:306 [inline]
BUG: KASAN: use-after-free in iterate_and_advance include/linux/iov_iter.h:330 [inline]
BUG: KASAN: use-after-free in __copy_from_iter lib/iov_iter.c:261 [inline]
BUG: KASAN: use-after-free in copy_folio_from_iter_atomic+0xb7c/0x164c lib/iov_iter.c:491
Read of size 4096 at addr ffff0000d64c3000 by task kworker/u8:7/642

CPU: 0 UID: 0 PID: 642 Comm: kworker/u8:7 Not tainted syzkaller #0 PREEMPT
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
Workqueue: loop2 loop_workfn
Call trace:
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
__dump_stack+0x30/0x40 lib/dump_stack.c:94
dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
print_address_description+0xa8/0x238 mm/kasan/report.c:378
print_report+0x68/0x84 mm/kasan/report.c:482
kasan_report+0xb0/0x110 mm/kasan/report.c:595
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x264/0x2a4 mm/kasan/generic.c:200
__asan_memcpy+0x3c/0x84 mm/kasan/shadow.c:105
memcpy_from_iter lib/iov_iter.c:85 [inline]
iterate_bvec include/linux/iov_iter.h:123 [inline]
iterate_and_advance2 include/linux/iov_iter.h:306 [inline]
iterate_and_advance include/linux/iov_iter.h:330 [inline]
__copy_from_iter lib/iov_iter.c:261 [inline]
copy_folio_from_iter_atomic+0xb7c/0x164c lib/iov_iter.c:491
generic_perform_write+0x4d0/0x7bc mm/filemap.c:4332
shmem_file_write_iter+0x10c/0x134 mm/shmem.c:3490
lo_rw_aio+0x8f4/0xa78 drivers/block/loop.c:-1
do_req_filebacked drivers/block/loop.c:-1 [inline]
loop_handle_cmd drivers/block/loop.c:1926 [inline]
loop_process_work+0x808/0x1058 drivers/block/loop.c:1961
loop_workfn+0x50/0x64 drivers/block/loop.c:1985
process_one_work+0x7c0/0x1558 kernel/workqueue.c:3257
process_scheduled_works kernel/workqueue.c:3340 [inline]
worker_thread+0x958/0xed8 kernel/workqueue.c:3421
kthread+0x5fc/0x75c kernel/kthread.c:463
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x25 pfn:0x1164c3
flags: 0x5ffc00000000000(node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000000000 fffffdffc3658c48 fffffdffc353db88 0000000000000000
raw: 0000000000000025 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff0000d64c2f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff0000d64c2f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff0000d64c3000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff0000d64c3080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff0000d64c3100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


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