KASAN: null-ptr-deref Write in xdp_umem_unaccount_pages

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 1c8c5a9d38f6 Merge git://git.kernel.org/pub/scm/linux/kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13a72bdf800000
kernel config: https://syzkaller.appspot.com/x/.config?x=4f1acdf888c9d4e9
dashboard link: https://syzkaller.appspot.com/bug?extid=979217770b09ebf5c407
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=12aca2af800000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=161d4ddf800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+979217...@syzkaller.appspotmail.com

RDX: 0000000000000004 RSI: 000000000000011b RDI: 0000000000000004
RBP: 00000000006cb018 R08: 0000000000000018 R09: 00007fffc4750032
R10: 0000000020000040 R11: 0000000000000246 R12: 0000000000000005
R13: ffffffffffffffff R14: 0000000000000000 R15: 0000000000000000
==================================================================
BUG: KASAN: null-ptr-deref in atomic64_sub
include/asm-generic/atomic-instrumented.h:144 [inline]
BUG: KASAN: null-ptr-deref in atomic_long_sub
include/asm-generic/atomic-long.h:199 [inline]
BUG: KASAN: null-ptr-deref in xdp_umem_unaccount_pages.isra.4+0x3d/0x80
net/xdp/xdp_umem.c:135
Write of size 8 at addr 0000000000000060 by task syz-executor246/4527

CPU: 1 PID: 4527 Comm: syz-executor246 Not tainted 4.17.0+ #89
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+0x1b9/0x294 lib/dump_stack.c:113
kasan_report_error mm/kasan/report.c:352 [inline]
kasan_report.cold.7+0x6d/0x2fe 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
kasan_check_write+0x14/0x20 mm/kasan/kasan.c:278
atomic64_sub include/asm-generic/atomic-instrumented.h:144 [inline]
atomic_long_sub include/asm-generic/atomic-long.h:199 [inline]
xdp_umem_unaccount_pages.isra.4+0x3d/0x80 net/xdp/xdp_umem.c:135
xdp_umem_reg net/xdp/xdp_umem.c:334 [inline]
xdp_umem_create+0xd6c/0x10f0 net/xdp/xdp_umem.c:349
xsk_setsockopt+0x443/0x550 net/xdp/xsk.c:531
__sys_setsockopt+0x1bd/0x390 net/socket.c:1935
__do_sys_setsockopt net/socket.c:1946 [inline]
__se_sys_setsockopt net/socket.c:1943 [inline]
__x64_sys_setsockopt+0xbe/0x150 net/socket.c:1943
do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440549
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 5b 14 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fffc475d008 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000440549
RDX: 0000000000000004 RSI: 000000000000011b RDI: 0000000000000004
RBP: 00000000006cb018 R08: 0000000000000018 R09: 00007fffc4750032
R10: 0000000020000040 R11: 0000000000000246 R12: 0000000000000005
R13: ffffffffffffffff R14: 0000000000000000 R15: 0000000000000000
==================================================================


---
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 syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Daniel Borkmann]

On 06/07/2018 08:17 PM, syzbot wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    1c8c5a9d38f6 Merge git://git.kernel.org/pub/scm/linux/kern..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13a72bdf800000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4f1acdf888c9d4e9
> dashboard link: https://syzkaller.appspot.com/bug?extid=979217770b09ebf5c407
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=12aca2af800000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=161d4ddf800000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+979217...@syzkaller.appspotmail.com

#syz fix: bpf, xdp: fix crash in xdp_umem_unaccount_pages