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

syzbot
2026-03-30T09:56:26Z

Hello,

syzbot found the following issue on:

HEAD commit: 24d479d26b25 Linux 6.19-rc6
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15454e3a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c33bf4a3a0c7a4f1
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

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f0555f920605/disk-24d479d2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ae277d28fcd2/vmlinux-24d479d2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b4f8db4a51a6/bzImage-24d479d2.xz

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+0xa6c/0x1950 lib/iov_iter.c:491
Read of size 4096 at addr ffff88803177d000 by task kworker/u8:9/1219

CPU: 0 UID: 0 PID: 1219 Comm: kworker/u8:9 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: loop1 loop_workfn
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xba/0x230 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+0xa6c/0x1950 lib/iov_iter.c:491
generic_perform_write+0x5b1/0x8b0 mm/filemap.c:4332
shmem_file_write_iter+0xfb/0x120 mm/shmem.c:3490
lo_rw_aio+0xc80/0xf00 include/linux/percpu-rwsem.h:-1
do_req_filebacked drivers/block/loop.c:434 [inline]
loop_handle_cmd drivers/block/loop.c:1947 [inline]
loop_process_work+0x637/0x11b0 drivers/block/loop.c:1982
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0xaec/0x17a0 kernel/workqueue.c:3340
worker_thread+0x89f/0xd90 kernel/workqueue.c:3421
kthread+0x726/0x8b0 kernel/kthread.c:463
ret_from_fork+0x51b/0xa40 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
</TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88803177d000 pfn:0x3177d
flags: 0x80000000000000(node=0|zone=1)
raw: 0080000000000000 ffffea00016beb08 ffffea00009e42c8 0000000000000000
raw: ffff88803177d000 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 6876, tgid 6875 (syz.1.137), ts 163020649815, free_ts 163886382057
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x228/0x280 mm/page_alloc.c:1884
prep_new_page mm/page_alloc.c:1892 [inline]
get_page_from_freelist+0x28bb/0x2950 mm/page_alloc.c:3945
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5240
alloc_pages_mpol+0xd1/0x380 mm/mempolicy.c:2486
alloc_frozen_pages_noprof mm/mempolicy.c:2557 [inline]
alloc_pages_noprof+0xce/0x1e0 mm/mempolicy.c:2577
lbmLogInit fs/jfs/jfs_logmgr.c:1815 [inline]
lmLogInit+0x357/0x1a00 fs/jfs/jfs_logmgr.c:1269
open_inline_log fs/jfs/jfs_logmgr.c:1175 [inline]
lmLogOpen+0x4e1/0xfa0 fs/jfs/jfs_logmgr.c:1069
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:1691
vfs_get_tree+0x92/0x2a0 fs/super.c:1751
fc_mount fs/namespace.c:1199 [inline]
do_new_mount_fc fs/namespace.c:3636 [inline]
do_new_mount+0x329/0xa50 fs/namespace.c:3712
do_mount fs/namespace.c:4035 [inline]
__do_sys_mount fs/namespace.c:4224 [inline]
__se_sys_mount+0x31d/0x420 fs/namespace.c:4201
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5804 tgid 5804 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1433 [inline]
__free_frozen_pages+0xfc1/0x1130 mm/page_alloc.c:2973
lbmLogShutdown fs/jfs/jfs_logmgr.c:1863 [inline]
lmLogShutdown+0x44e/0x850 fs/jfs/jfs_logmgr.c:1683
lmLogClose+0x28a/0x520 fs/jfs/jfs_logmgr.c:1459
jfs_umount+0x2ef/0x3c0 fs/jfs/jfs_umount.c:114
jfs_put_super+0x8c/0x190 fs/jfs/super.c:194
generic_shutdown_super+0x135/0x2c0 fs/super.c:643
kill_block_super+0x44/0x90 fs/super.c:1722
deactivate_locked_super+0xbc/0x130 fs/super.c:474
cleanup_mnt+0x437/0x4d0 fs/namespace.c:1318
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:44 [inline]
exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:75
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
do_syscall_64+0x2b7/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff88803177cf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88803177cf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88803177d000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff88803177d080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88803177d100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================

---
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