[syzbot] [bpf?] [net?] KASAN: null-ptr-deref Write in unix_stream_bpf_update_proto

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 300fbb247eb3 Merge tag 'wireless-2023-11-29' of git://git...
git tree: net
console+strace: https://syzkaller.appspot.com/x/log.txt?x=115f1a54e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=6ae1a4ee971a7305
dashboard link: https://syzkaller.appspot.com/bug?extid=e8030702aefd3444fb9e
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16929b52e80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=108a528ce80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/882903ce12c3/disk-300fbb24.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bd633c35425c/vmlinux-300fbb24.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e400d04e154e/bzImage-300fbb24.xz

The issue was bisected to:

commit 8866730aed5100f06d3d965c22f1c61f74942541
Author: John Fastabend <john.fa...@gmail.com>
Date: Wed Nov 29 01:25:56 2023 +0000

bpf, sockmap: af_unix stream sockets need to hold ref for pair sock

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1635a52ce80000
final oops: https://syzkaller.appspot.com/x/report.txt?x=1535a52ce80000
console output: https://syzkaller.appspot.com/x/log.txt?x=1135a52ce80000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e80307...@syzkaller.appspotmail.com
Fixes: 8866730aed51 ("bpf, sockmap: af_unix stream sockets need to hold ref for pair sock")

==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
BUG: KASAN: null-ptr-deref in atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
BUG: KASAN: null-ptr-deref in __refcount_add include/linux/refcount.h:193 [inline]
BUG: KASAN: null-ptr-deref in __refcount_inc include/linux/refcount.h:250 [inline]
BUG: KASAN: null-ptr-deref in refcount_inc include/linux/refcount.h:267 [inline]
BUG: KASAN: null-ptr-deref in sock_hold include/net/sock.h:777 [inline]
BUG: KASAN: null-ptr-deref in unix_stream_bpf_update_proto+0x72/0x430 net/unix/unix_bpf.c:171
Write of size 4 at addr 0000000000000080 by task syz-executor360/5073

CPU: 1 PID: 5073 Comm: syz-executor360 Not tainted 6.7.0-rc2-syzkaller-00143-g300fbb247eb3 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
kasan_report+0xda/0x110 mm/kasan/report.c:588
check_region_inline mm/kasan/generic.c:181 [inline]
kasan_check_range+0xef/0x190 mm/kasan/generic.c:187
instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
__refcount_add include/linux/refcount.h:193 [inline]
__refcount_inc include/linux/refcount.h:250 [inline]
refcount_inc include/linux/refcount.h:267 [inline]
sock_hold include/net/sock.h:777 [inline]
unix_stream_bpf_update_proto+0x72/0x430 net/unix/unix_bpf.c:171
sock_map_init_proto net/core/sock_map.c:190 [inline]
sock_map_link+0xb87/0x1100 net/core/sock_map.c:294
sock_map_update_common+0xf6/0x870 net/core/sock_map.c:483
sock_map_update_elem_sys+0x5b6/0x640 net/core/sock_map.c:577
bpf_map_update_value+0x3af/0x820 kernel/bpf/syscall.c:167
map_update_elem+0x622/0x890 kernel/bpf/syscall.c:1526
__sys_bpf+0x1bfb/0x4920 kernel/bpf/syscall.c:5371
__do_sys_bpf kernel/bpf/syscall.c:5487 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5485 [inline]
__x64_sys_bpf+0x78/0xc0 kernel/bpf/syscall.c:5485
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7f1c8f3fe369
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd877e4a58 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007ffd877e4c28 RCX: 00007f1c8f3fe369
RDX: 0000000000000020 RSI: 0000000020000140 RDI: 0000000000000002
RBP: 00007f1c8f471610 R08: 00007ffd877e4c28 R09: 00007ffd877e4c28
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffd877e4c18 R14: 0000000000000001 R15: 0000000000000001
</TASK>
==================================================================


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