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

[syzbot <syzbot+6cc93ec9a4035badb85f@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: use-after-free Read in copy_folio_from_iter_atomic

==================================================================
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 ffff88802b268000 by task kworker/u8:5/144

CPU: 0 UID: 0 PID: 144 Comm: kworker/u8:5 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
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:4343
 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:3302 [inline]
 process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3385
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3466
 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:0xffff88802b268000 pfn:0x2b268
flags: 0x80000000000000(node=0|zone=1)
raw: 0080000000000000 ffffea0000d2af88 ffffea0000a9b208 0000000000000000
raw: ffff88802b268000 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 6562, tgid 6561 (syz.0.36), ts 165655705395, free_ts 165814306670
 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+0x27c8/0x2840 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+0x359/0x1a40 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:4383 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4360
 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 6409 tgid 6409 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1402 [inline]
 __free_frozen_pages+0xfa6/0x10f0 mm/page_alloc.c:2943
 lbmLogShutdown fs/jfs/jfs_logmgr.c:1863 [inline]
 lmLogShutdown+0x45f/0x870 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:318 [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:
 ffff88802b267f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88802b267f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88802b268000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff88802b268080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88802b268100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


Tested on:

commit:         2e680392 Merge tag 'tracefs-v7.1-2' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1023ff16580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=80b28e8d6ef9384a
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
patch:          https://syzkaller.appspot.com/x/patch.diff?x=16bdff16580000