KASAN: null-ptr-deref Read in xattr_getsecurity

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
1b88accf6a659c46d5c8e68912896f112bf882bb (Thu Mar 8 01:49:33 2018 +0000)
Merge tag 'for_linus' of
git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.
user-space arch: i386
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org
vi...@zeniv.linux.org.uk]

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Reported-by: syzbot+3933c3...@syzkaller.appspotmail.com
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RDX: 0000000020000280 RSI: 00000000000001db RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
==================================================================
BUG: KASAN: null-ptr-deref in memcpy include/linux/string.h:345 [inline]
BUG: KASAN: null-ptr-deref in xattr_getsecurity+0x11d/0x1f0 fs/xattr.c:251
Read of size 20 at addr 0000000000000000 by task syz-executor3/10404

CPU: 1 PID: 10404 Comm: syz-executor3 Not tainted 4.16.0-rc4+ #256
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x24d lib/dump_stack.c:53
kasan_report_error mm/kasan/report.c:352 [inline]
kasan_report+0x140/0x360 mm/kasan/report.c:412
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x137/0x190 mm/kasan/kasan.c:267
memcpy+0x23/0x50 mm/kasan/kasan.c:302
memcpy include/linux/string.h:345 [inline]
xattr_getsecurity+0x11d/0x1f0 fs/xattr.c:251
vfs_getxattr+0xc8/0x110 fs/xattr.c:333
getxattr+0x116/0x2a0 fs/xattr.c:540
SYSC_fgetxattr fs/xattr.c:598 [inline]
SyS_fgetxattr+0xe2/0x150 fs/xattr.c:589
do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
do_fast_syscall_32+0x3ec/0xf9f arch/x86/entry/common.c:392
binder: 10435:10444 BC_INCREFS_DONE u0000000020000580 no match
binder: 10435:10444 BC_INCREFS_DONE u0000000000000000 no match
binder: 10435:10444 unknown command 0
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f91c99
RSP: 002b:00000000f778d09c EFLAGS: 00000286 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000013 RCX: 0000000020000000
binder: 10435:10444 ioctl c0306201 20000540 returned -22
RDX: 0000000020000280 RSI: 00000000000001db RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
==================================================================
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 10404 Comm: syz-executor3 Tainted: G B
4.16.0-rc4+ #256
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x24d lib/dump_stack.c:53
panic+0x1e4/0x41c kernel/panic.c:183
kasan_end_report+0x50/0x50 mm/kasan/report.c:180
kasan_report_error mm/kasan/report.c:359 [inline]
kasan_report+0x149/0x360 mm/kasan/report.c:412
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x137/0x190 mm/kasan/kasan.c:267
memcpy+0x23/0x50 mm/kasan/kasan.c:302
memcpy include/linux/string.h:345 [inline]
xattr_getsecurity+0x11d/0x1f0 fs/xattr.c:251
vfs_getxattr+0xc8/0x110 fs/xattr.c:333
getxattr+0x116/0x2a0 fs/xattr.c:540
SYSC_fgetxattr fs/xattr.c:598 [inline]
SyS_fgetxattr+0xe2/0x150 fs/xattr.c:589
do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
do_fast_syscall_32+0x3ec/0xf9f arch/x86/entry/common.c:392
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f91c99
RSP: 002b:00000000f778d09c EFLAGS: 00000286 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000013 RCX: 0000000020000000
RDX: 0000000020000280 RSI: 00000000000001db RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[Dmitry Vyukov]

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