[syzbot] KASAN: use-after-free Read in copy_page_from_iter_atomic (2)

syzbot
2022-06-07T13:11:33Z

Hello,

syzbot found the following issue on:

HEAD commit: 73d0e32571a0 Add linux-next specific files for 20220607
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1433bacff00000
kernel config: https://syzkaller.appspot.com/x/.config?x=448ee2b64e828049
dashboard link: https://syzkaller.appspot.com/bug?extid=d2dd123304b4ae59f1bd
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d2dd123304b4ae59f1bd@syzkaller.appspotmail.com

BTRFS error (device loop2): bad tree block start, want 22036480 have 0
==================================================================
BUG: KASAN: use-after-free in copy_page_from_iter_atomic+0xef6/0x1b30 lib/iov_iter.c:969
Read of size 4096 at addr ffff888177101000 by task kworker/u4:30/4131

CPU: 0 PID: 4131 Comm: kworker/u4:30 Not tainted 5.19.0-rc1-next-20220607-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: loop2 loop_workfn
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
print_address_description.constprop.0.cold+0xeb/0x495 mm/kasan/report.c:313
print_report mm/kasan/report.c:429 [inline]
kasan_report.cold+0xf4/0x1c6 mm/kasan/report.c:491
check_region_inline mm/kasan/generic.c:183 [inline]
kasan_check_range+0x13d/0x180 mm/kasan/generic.c:189
memcpy+0x20/0x60 mm/kasan/shadow.c:65
copy_page_from_iter_atomic+0xef6/0x1b30 lib/iov_iter.c:969
generic_perform_write+0x2b8/0x560 mm/filemap.c:3734
__generic_file_write_iter+0x2aa/0x4d0 mm/filemap.c:3854
generic_file_write_iter+0xd7/0x220 mm/filemap.c:3886
call_write_iter include/linux/fs.h:2059 [inline]
do_iter_readv_writev+0x3d1/0x640 fs/read_write.c:742
do_iter_write+0x182/0x700 fs/read_write.c:868
vfs_iter_write+0x70/0xa0 fs/read_write.c:909
lo_write_bvec drivers/block/loop.c:249 [inline]
lo_write_simple drivers/block/loop.c:271 [inline]
do_req_filebacked drivers/block/loop.c:495 [inline]
loop_handle_cmd drivers/block/loop.c:1859 [inline]
loop_process_work+0xd83/0x2050 drivers/block/loop.c:1894
process_one_work+0x996/0x1610 kernel/workqueue.c:2289
worker_thread+0x665/0x1080 kernel/workqueue.c:2436
kthread+0x2e9/0x3a0 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:302
</TASK>

The buggy address belongs to the physical page:
page:ffffea0005dc4040 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x177101
flags: 0x57ff00000000000(node=1|zone=2|lastcpupid=0x7ff)
raw: 057ff00000000000 ffffea0005dc4048 ffffea0005dc4048 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner info is not present (never set?)

Memory state around the buggy address:
ffff888177100f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888177100f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888177101000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff888177101080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888177101100: 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 syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.