bisecting fixing commit since 8fe28cb58bcb235034b64cbbb7550a8a43fd88be
building syzkaller on 8a41a0ad8ed91a6c7a65663b1bacaf6d79cde558
testing commit 8fe28cb58bcb235034b64cbbb7550a8a43fd88be with gcc (GCC) 8.1.0
all runs: crashed: KASAN: stack-out-of-bounds Write in ax25_getname
testing current HEAD 00aff6836241ae5654895dcea10e6d4fc5878ca6
testing commit 00aff6836241ae5654895dcea10e6d4fc5878ca6 with gcc (GCC) 8.1.0
all runs: crashed: KASAN: stack-out-of-bounds Write in ax25_getname
revisions tested: 2, total time: 21m14.063097709s (build: 12m36.740847299s, test: 7m24.48880367s)
the crash still happens on HEAD
commit msg: Merge tag 'for-5.4-rc6-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux
crash: KASAN: stack-out-of-bounds Write in ax25_getname
8021q: adding VLAN 0 to HW filter on device team0
IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
8021q: adding VLAN 0 to HW filter on device team0
==================================================================
BUG: KASAN: stack-out-of-bounds in memset include/linux/string.h:363 [inline]
BUG: KASAN: stack-out-of-bounds in ax25_getname+0x4d/0x7b0 net/ax25/af_ax25.c:1405
Write of size 72 at addr ffff8881b8c67c78 by task syz-executor3/9222

CPU: 0 PID: 9222 Comm: syz-executor3 Not tainted 5.4.0-rc6+ #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+0x12d/0x187 lib/dump_stack.c:118
 print_address_description.constprop.8.cold.10+0x9/0x31d mm/kasan/report.c:374
 __kasan_report.cold.11+0x1b/0x3a mm/kasan/report.c:506
 kasan_report+0x12/0x20 mm/kasan/common.c:634
 check_memory_region_inline mm/kasan/generic.c:185 [inline]
 check_memory_region+0x153/0x1d0 mm/kasan/generic.c:192
 memset+0x23/0x40 mm/kasan/common.c:105
 memset include/linux/string.h:363 [inline]
 ax25_getname+0x4d/0x7b0 net/ax25/af_ax25.c:1405
 get_raw_socket drivers/vhost/net.c:1433 [inline]
 get_socket drivers/vhost/net.c:1489 [inline]
 vhost_net_set_backend drivers/vhost/net.c:1524 [inline]
 vhost_net_ioctl+0xe79/0x1530 drivers/vhost/net.c:1715
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0x199/0x1160 fs/ioctl.c:696
 ksys_ioctl+0x62/0x90 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:718
 do_syscall_64+0xd0/0x5e0 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4578a9
Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fd47c00bc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004578a9
RDX: 0000000020f1dff8 RSI: 000000004008af30 RDI: 0000000000000004
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fd47c00c6d4
R13: 00000000004c1e74 R14: 00000000004d4180 R15: 00000000ffffffff

The buggy address belongs to the page:
page:ffffea0006e319c0 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 ffffffff06e30101 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

addr ffff8881b8c67c78 is located in stack of task syz-executor3/9222 at offset 160 in frame:
 vhost_net_ioctl+0x0/0x1530 drivers/vhost/net.c:1245

this frame has 3 objects:
 [32, 36) 'r'
 [96, 104) 'backend'
 [160, 212) 'uaddr'

Memory state around the buggy address:
 ffff8881b8c67b80: 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 04
 ffff8881b8c67c00: f2 f2 f2 f2 f2 f2 f2 00 f2 f2 f2 f2 f2 f2 f2 00
>ffff8881b8c67c80: 00 00 00 00 00 04 f2 00 00 00 00 00 00 00 00 00
                                  ^
 ffff8881b8c67d00: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 f2 f2 f2
 ffff8881b8c67d80: f2 f2 f2 f2 00 00 00 f2 f2 f2 f2 f2 00 00 00 00
==================================================================