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

syzbot
2026-04-16T10:23:34Z

syzbot has found a reproducer for the following issue on:

HEAD commit: e6efabc0afca Add linux-next specific files for 20260414
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17908702580000
kernel config: https://syzkaller.appspot.com/x/.config?x=56c2b36de3316f1b
dashboard link: https://syzkaller.appspot.com/bug?extid=6cc93ec9a4035badb85f
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14c798ce580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1142c4ce580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e7099cbf73e4/disk-e6efabc0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/439c402df1b9/vmlinux-e6efabc0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fc0c0175fc76/bzImage-e6efabc0.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/94fa7bad6be9/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=17017b16580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6cc93ec9a4035badb85f@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+0xbb5/0x1ad0 lib/iov_iter.c:491
Read of size 4096 at addr ffff888037cb3000 by task kworker/u8:7/1020

CPU: 0 UID: 0 PID: 1020 Comm: kworker/u8:7 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Workqueue: loop0 loop_workfn
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description+0x55/0x1e0 mm/kasan/report.c:378
print_report+0x58/0x70 mm/kasan/report.c:482
kasan_report+0x117/0x150 mm/kasan/report.c:595
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
__asan_memcpy+0x29/0x70 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+0xbb5/0x1ad0 lib/iov_iter.c:491
generic_perform_write+0x5b1/0x8b0 mm/filemap.c:4342
shmem_file_write_iter+0xfb/0x120 mm/shmem.c:3478
lo_rw_aio+0xc80/0xf00 include/linux/percpu-rwsem.h:-1
do_req_filebacked drivers/block/loop.c:433 [inline]
loop_handle_cmd drivers/block/loop.c:1925 [inline]
loop_process_work+0x637/0x11b0 drivers/block/loop.c:1960
process_one_work kernel/workqueue.c:3308 [inline]
process_scheduled_works+0xb68/0x1910 kernel/workqueue.c:3399
worker_thread+0xa90/0x1040 kernel/workqueue.c:3485
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x38 pfn:0x37cb3
flags: 0x80000000000000(node=0|zone=1)
raw: 0080000000000000 ffffea0000d17548 ffffea0001353448 0000000000000000
raw: 0000000000000038 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xdc0(GFP_KERNEL|__GFP_ZERO), pid 6098, tgid 6098 (syz.0.91), ts 154383709391, free_ts 154428922615
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x231/0x280 mm/page_alloc.c:1858
prep_new_page mm/page_alloc.c:1866 [inline]
get_page_from_freelist+0x27d6/0x2850 mm/page_alloc.c:3946
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5226
alloc_pages_mpol+0xd1/0x380 mm/mempolicy.c:2490
alloc_frozen_pages_noprof mm/mempolicy.c:2561 [inline]
alloc_pages_noprof+0xd2/0x2f0 mm/mempolicy.c:2581
lbmLogInit fs/jfs/jfs_logmgr.c:1813 [inline]
lmLogInit+0x357/0x1a00 fs/jfs/jfs_logmgr.c:1267
open_inline_log fs/jfs/jfs_logmgr.c:1173 [inline]
lmLogOpen+0x4e1/0xfa0 fs/jfs/jfs_logmgr.c:1067
jfs_mount_rw+0xee/0x670 fs/jfs/jfs_mount.c:257
jfs_fill_super+0x754/0xd80 fs/jfs/super.c:532
get_tree_bdev_flags+0x431/0x4f0 fs/super.c:1694
vfs_get_tree+0x92/0x2a0 fs/super.c:1754
fc_mount fs/namespace.c:1193 [inline]
do_new_mount_fc fs/namespace.c:3758 [inline]
do_new_mount+0x341/0xd30 fs/namespace.c:3834
do_mount fs/namespace.c:4167 [inline]
__do_sys_mount fs/namespace.c:4399 [inline]
__se_sys_mount+0x31d/0x420 fs/namespace.c:4376
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5945 tgid 5945 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1402 [inline]
__free_frozen_pages+0xf9b/0x10f0 mm/page_alloc.c:2943
lbmLogShutdown fs/jfs/jfs_logmgr.c:1861 [inline]
lmLogShutdown+0x44e/0x850 fs/jfs/jfs_logmgr.c:1681
lmLogClose+0x28a/0x520 fs/jfs/jfs_logmgr.c:1457
jfs_umount+0x2fb/0x3d0 fs/jfs/jfs_umount.c:124
jfs_put_super+0x8c/0x190 fs/jfs/super.c:194
generic_shutdown_super+0x13d/0x2d0 fs/super.c:646
kill_block_super+0x44/0x90 fs/super.c:1725
deactivate_locked_super+0xbc/0x130 fs/super.c:476
cleanup_mnt+0x437/0x4d0 fs/namespace.c:1312
task_work_run+0x1d9/0x270 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:328 [inline]
do_syscall_64+0x33e/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff888037cb2f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888037cb2f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888037cb3000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff888037cb3080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888037cb3100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================

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