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SubjectKASAN: use-after-free Read in iov_iter_alignment
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Hello,

syzbot found the following crash on:

HEAD commit: b94ae8ad Merge tag 'seccomp-v5.5-rc1' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=135a8d7ae00000
kernel config: https://syzkaller.appspot.com/x/.config?x=c2e464ae414aee8c
dashboard link: https://syzkaller.appspot.com/bug?extid=bea68382bae9490e7dd6
compiler: clang version 9.0.0 (/home/glider/llvm/clang
80fee25776c2fb61e74c1ecb1a523375c2500b69)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1135cb36e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14e90abce00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+bea68382bae9490e7dd6@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in iov_iter_alignment+0x6a1/0x7b0
lib/iov_iter.c:1225
Read of size 4 at addr ffff888098d40f54 by task loop0/8203

CPU: 0 PID: 8203 Comm: loop0 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1fb/0x318 lib/dump_stack.c:118
print_address_description+0x75/0x5c0 mm/kasan/report.c:374
__kasan_report+0x14b/0x1c0 mm/kasan/report.c:506
kasan_report+0x26/0x50 mm/kasan/common.c:634
__asan_report_load4_noabort+0x14/0x20 mm/kasan/generic_report.c:131
iov_iter_alignment+0x6a1/0x7b0 lib/iov_iter.c:1225
iomap_dio_bio_actor+0x1a7/0x11e0 fs/iomap/direct-io.c:203
iomap_dio_actor+0x2b4/0x4a0 fs/iomap/direct-io.c:375
iomap_apply+0x370/0x490 fs/iomap/apply.c:80
iomap_dio_rw+0x8ad/0x1010 fs/iomap/direct-io.c:493
ext4_dio_read_iter fs/ext4/file.c:77 [inline]
ext4_file_read_iter+0x834/0xc20 fs/ext4/file.c:128
lo_rw_aio+0xcbb/0xea0 include/linux/fs.h:1889
do_req_filebacked drivers/block/loop.c:616 [inline]
loop_handle_cmd drivers/block/loop.c:1952 [inline]
loop_queue_work+0x13ab/0x2590 drivers/block/loop.c:1966
kthread_worker_fn+0x449/0x700 kernel/kthread.c:671
loop_kthread_worker_fn+0x40/0x60 drivers/block/loop.c:901
kthread+0x332/0x350 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 4198:
save_stack mm/kasan/common.c:69 [inline]
set_track mm/kasan/common.c:77 [inline]
__kasan_kmalloc+0x11c/0x1b0 mm/kasan/common.c:510
kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:518
slab_post_alloc_hook mm/slab.h:584 [inline]
slab_alloc mm/slab.c:3319 [inline]
kmem_cache_alloc+0x1f5/0x2e0 mm/slab.c:3483
mempool_alloc_slab+0x4d/0x70 mm/mempool.c:513
mempool_alloc+0x104/0x5e0 mm/mempool.c:393
bio_alloc_bioset+0x1b0/0x5f0 block/bio.c:477
bio_alloc include/linux/bio.h:400 [inline]
mpage_alloc fs/mpage.c:79 [inline]
do_mpage_readpage+0x1685/0x1d10 fs/mpage.c:306
mpage_readpages+0x2a9/0x440 fs/mpage.c:404
blkdev_readpages+0x2c/0x40 fs/block_dev.c:620
read_pages+0xad/0x4d0 mm/readahead.c:126
__do_page_cache_readahead+0x480/0x530 mm/readahead.c:212
force_page_cache_readahead mm/readahead.c:243 [inline]
page_cache_sync_readahead+0x329/0x3b0 mm/readahead.c:522
generic_file_buffered_read+0x41d/0x2570 mm/filemap.c:2051
generic_file_read_iter+0xa9/0x450 mm/filemap.c:2324
blkdev_read_iter+0x12e/0x140 fs/block_dev.c:2039
call_read_iter include/linux/fs.h:1889 [inline]
new_sync_read fs/read_write.c:414 [inline]
__vfs_read+0x59e/0x730 fs/read_write.c:427
vfs_read+0x1dd/0x420 fs/read_write.c:461
ksys_read+0x117/0x220 fs/read_write.c:587
__do_sys_read fs/read_write.c:597 [inline]
__se_sys_read fs/read_write.c:595 [inline]
__x64_sys_read+0x7b/0x90 fs/read_write.c:595
do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 4205:
save_stack mm/kasan/common.c:69 [inline]
set_track mm/kasan/common.c:77 [inline]
kasan_set_free_info mm/kasan/common.c:332 [inline]
__kasan_slab_free+0x12a/0x1e0 mm/kasan/common.c:471
kasan_slab_free+0xe/0x10 mm/kasan/common.c:480
__cache_free mm/slab.c:3425 [inline]
kmem_cache_free+0x81/0xf0 mm/slab.c:3693
mempool_free_slab+0x1d/0x30 mm/mempool.c:520
mempool_free+0xd5/0x350 mm/mempool.c:502
bio_put+0x38b/0x460 block/bio.c:255
mpage_end_io+0x2f5/0x330 fs/mpage.c:58
bio_endio+0x4ff/0x570 block/bio.c:1818
req_bio_endio block/blk-core.c:245 [inline]
blk_update_request+0x438/0x10d0 block/blk-core.c:1464
scsi_end_request+0x8c/0xa20 drivers/scsi/scsi_lib.c:579
scsi_io_completion+0x17c/0x1b80 drivers/scsi/scsi_lib.c:963
scsi_finish_command+0x3b3/0x560 drivers/scsi/scsi.c:228
scsi_softirq_done+0x289/0x310 drivers/scsi/scsi_lib.c:1477
blk_done_softirq+0x312/0x370 block/blk-softirq.c:37
__do_softirq+0x333/0x7c4 arch/x86/include/asm/paravirt.h:762

The buggy address belongs to the object at ffff888098d40f00
which belongs to the cache bio-0 of size 192
The buggy address is located 84 bytes inside of
192-byte region [ffff888098d40f00, ffff888098d40fc0)
The buggy address belongs to the page:
page:ffffea0002635000 refcount:1 mapcount:0 mapping:ffff88821acf5700
index:0xffff888098d40c00
raw: 00fffe0000000200 ffffea0002805188 ffff8880a7b42738 ffff88821acf5700
raw: ffff888098d40c00 ffff888098d40000 000000010000000e 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888098d40e00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888098d40e80: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
> ffff888098d40f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888098d40f80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff888098d41000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This bug 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 bug report. See:
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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