KASAN: stack-out-of-bounds Write in read_extent_buffer

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    860461e4 Add linux-next specific files for 20200917
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=141fc5d9900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f2392812d6c63d5c
dashboard link: https://syzkaller.appspot.com/bug?extid=1d393803acac53c985a0
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16778b07900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1216f8ad900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1d393803acac53c985a0@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: stack-out-of-bounds in memcpy include/linux/string.h:399 [inline]
BUG: KASAN: stack-out-of-bounds in read_extent_buffer+0x114/0x150 fs/btrfs/extent_io.c:5674
Write of size 8 at addr ffffc90000dd79f0 by task kworker/u4:1/21

CPU: 1 PID: 21 Comm: kworker/u4:1 Not tainted 5.9.0-rc5-next-20200917-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: btrfs-endio-meta btrfs_work_helper
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x198/0x1fb lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0x5/0x497 mm/kasan/report.c:385
 __kasan_report mm/kasan/report.c:545 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:562
 check_memory_region_inline mm/kasan/generic.c:186 [inline]
 check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
 memcpy+0x39/0x60 mm/kasan/common.c:106
 memcpy include/linux/string.h:399 [inline]
 read_extent_buffer+0x114/0x150 fs/btrfs/extent_io.c:5674
 btree_readpage_end_io_hook+0x7de/0x950 fs/btrfs/disk-io.c:641
 end_bio_extent_readpage+0x4de/0x10c0 fs/btrfs/extent_io.c:2854
 bio_endio+0x3d3/0x7a0 block/bio.c:1449
 end_workqueue_fn+0x114/0x170 fs/btrfs/disk-io.c:1696
 btrfs_work_helper+0x20a/0xd20 fs/btrfs/async-thread.c:318
 process_one_work+0x933/0x15a0 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x3af/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296


addr ffffc90000dd79f0 is located in stack of task kworker/u4:1/21 at offset 48 in frame:
 btree_readpage_end_io_hook+0x0/0x950 fs/btrfs/disk-io.c:201

this frame has 4 objects:
 [48, 52) 'val'
 [64, 80) 'fsid'
 [96, 128) 'result'
 [160, 192) 'found'

Memory state around the buggy address:
 ffffc90000dd7880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffc90000dd7900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffc90000dd7980: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 f1 f1 04 f2
                                                             ^
 ffffc90000dd7a00: 00 00 f2 f2 00 00 00 00 f2 f2 f2 f2 00 00 00 00
 ffffc90000dd7a80: f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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