KASAN: stack-out-of-bounds Read in _copy_to_iter

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7a35a50df5a3 neighbor: Add extack messages for add and del..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=132865a3400000
kernel config: https://syzkaller.appspot.com/x/.config?x=28ecefa8a6e10719
dashboard link: https://syzkaller.appspot.com/bug?extid=06487665efbf15216e90
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [crec...@redhat.com kees...@chromium.org
linux-...@vger.kernel.org linu...@kvack.org]

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+064876...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: stack-out-of-bounds in memcpy include/linux/string.h:352
[inline]
BUG: KASAN: stack-out-of-bounds in _copy_to_iter+0xd2f/0x1440
lib/iov_iter.c:570
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
Read of size 128 at addr ffff8881dad81000 by task kworker/u4:4/15489

CPU: 1 PID: 15489 Comm: kworker/u4:4 Not tainted 4.20.0-rc4+ #329
general protection fault: 0000 [#1] PREEMPT SMP KASAN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
CPU: 0 PID: 15461 Comm: syz-executor0 Not tainted 4.20.0-rc4+ #329
Call Trace:
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x244/0x39d lib/dump_stack.c:113
RIP: 0010:vmalloc_fault+0x426/0x770 arch/x86/mm/fault.c:405
------------[ cut here ]------------
Bad or missing usercopy whitelist? Kernel memory overwrite attempt detected
to SLAB object ' ' (offset 18446744069414615263, size 64)!
WARNING: CPU: 0 PID: 15461 at mm/usercopy.c:83 usercopy_warn+0xee/0x110
mm/usercopy.c:78
print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
Kernel panic - not syncing: panic_on_warn set ...
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
memcpy+0x23/0x50 mm/kasan/kasan.c:302
memcpy include/linux/string.h:352 [inline]
_copy_to_iter+0xd2f/0x1440 lib/iov_iter.c:570
copy_to_iter include/linux/uio.h:143 [inline]
copy_page_to_iter+0x6e3/0x1000 lib/iov_iter.c:841
generic_file_buffered_read mm/filemap.c:2112 [inline]
generic_file_read_iter+0xcf0/0x2d70 mm/filemap.c:2289
ext4_file_read_iter+0x18b/0x3c0 fs/ext4/file.c:77
call_read_iter include/linux/fs.h:1851 [inline]
new_sync_read fs/read_write.c:406 [inline]
__vfs_read+0x6ac/0x9b0 fs/read_write.c:418
vfs_read+0x17f/0x3c0 fs/read_write.c:452
kernel_read+0xab/0x120 fs/read_write.c:431
prepare_binprm+0x73b/0xab0 fs/exec.c:1582
__do_execve_file.isra.33+0x137a/0x25d0 fs/exec.c:1801
do_execveat_common fs/exec.c:1867 [inline]
do_execve+0x33/0x40 fs/exec.c:1884
call_usermodehelper_exec_async+0x6cf/0xa80 kernel/umh.c:107
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352

The buggy address belongs to the page:
page:ffffea00076b6040 count:2 mapcount:0 mapping:ffff8881cc4eea70 index:0x0
flags: 0x2fffc0000020036(referenced|uptodate|lru|active|mappedtodisk)
raw: 02fffc0000020036 ffffea00076b6008 ffffea00076b5a08 ffff8881cc4eea70
raw: 0000000000000000 0000000000000000 00000002ffffffff ffff8881d9a46b80
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff8881d9a46b80

Memory state around the buggy address:
ffff8881dad80f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8881dad80f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1
> ffff8881dad81000: f1 00 f2 f2 f2 f2 f2 f2 f2 f8 f2 f2 f2 00 00 00
^
ffff8881dad81080: 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1
ffff8881dad81100: f1 f8 f2 f2 f2 00 00 00 00 00 00 00 00 00 00 00
==================================================================
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.