[Android 5.15] general protection fault in unix_stream_recv_urg

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 64205e2c7d13 Merge bb38ff8b4daf ("NFSD: Prevent lock owner..
git tree: android13-5.15-lts
console+strace: https://syzkaller.appspot.com/x/log.txt?x=11a13ac9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b0ecca01ee1a007b
dashboard link: https://syzkaller.appspot.com/bug?extid=2f15b05458b8b812b606
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13a13ac9580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=114d3605580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d80a40e67ce3/disk-64205e2c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bb9315a8b1af/vmlinux-64205e2c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e5623eb39183/bzImage-64205e2c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2f15b0...@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xdffffc000000000e: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000070-0x0000000000000077]
CPU: 1 PID: 306 Comm: syz-executor336 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:unix_skb_len net/unix/af_unix.c:523 [inline]
RIP: 0010:unix_stream_recv_urg+0x1a0/0x590 net/unix/af_unix.c:2537
Code: f7 49 89 cc e8 91 23 85 fd 4c 89 e1 4d 8b 36 49 39 ce 4d 8d a7 80 03 00 00 0f 84 9f 01 00 00 49 8d 7e 70 48 89 f8 48 c1 e8 03 <42> 0f b6 04 28 84 c0 0f 85 83 03 00 00 45 8b 66 70 4c 89 75 c8 49
RSP: 0018:ffffc900009873d8 EFLAGS: 00010202
RAX: 000000000000000e RBX: ffffc900009876c0 RCX: ffff88811e017a90
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000070
RBP: ffffc90000987430 R08: ffff88811e017a27 R09: 1ffff11023c02f44
R10: dffffc0000000000 R11: ffffed1023c02f45 R12: ffff88811e017d40
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff88811e0179c0
FS: 000055558a01e3c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000040 CR3: 0000000125821000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
unix_stream_read_generic+0x205b/0x2110 net/unix/af_unix.c:2644
__unix_stream_recvmsg+0xf8/0x150 net/unix/af_unix.c:2852
__unix_recvmsg net/unix/unix_bpf.c:47 [inline]
unix_bpf_recvmsg+0xa92/0xb70 net/unix/unix_bpf.c:-1
unix_stream_recvmsg+0x156/0x1d0 net/unix/af_unix.c:2871
____sys_recvmsg+0x2ca/0x5b0 net/socket.c:-1
___sys_recvmsg+0x213/0x5c0 net/socket.c:2697
__sys_recvmsg net/socket.c:2727 [inline]
__do_sys_recvmsg net/socket.c:2737 [inline]
__se_sys_recvmsg net/socket.c:2734 [inline]
__x64_sys_recvmsg+0x1fe/0x2d0 net/socket.c:2734
x64_sys_call+0x705/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:48
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f93665a3809
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 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 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe5315e678 EFLAGS: 00000246 ORIG_RAX: 000000000000002f
RAX: ffffffffffffffda RBX: 00002000000002c0 RCX: 00007f93665a3809
RDX: 0000000000002001 RSI: 0000200000000a80 RDI: 0000000000000004
RBP: 0000000000000000 R08: 0000000000000006 R09: 0000000000000006
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f9366636c40 R15: 0000000000000002
</TASK>
Modules linked in:
---[ end trace 4b0d0aa098f927ff ]---
RIP: 0010:unix_skb_len net/unix/af_unix.c:523 [inline]
RIP: 0010:unix_stream_recv_urg+0x1a0/0x590 net/unix/af_unix.c:2537
Code: f7 49 89 cc e8 91 23 85 fd 4c 89 e1 4d 8b 36 49 39 ce 4d 8d a7 80 03 00 00 0f 84 9f 01 00 00 49 8d 7e 70 48 89 f8 48 c1 e8 03 <42> 0f b6 04 28 84 c0 0f 85 83 03 00 00 45 8b 66 70 4c 89 75 c8 49
RSP: 0018:ffffc900009873d8 EFLAGS: 00010202

RAX: 000000000000000e RBX: ffffc900009876c0 RCX: ffff88811e017a90
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000070
RBP: ffffc90000987430 R08: ffff88811e017a27 R09: 1ffff11023c02f44
R10: dffffc0000000000 R11: ffffed1023c02f45 R12: ffff88811e017d40
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff88811e0179c0
FS: 000055558a01e3c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000040 CR3: 0000000125821000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: f7 49 89 cc e8 91 23 testl $0x2391e8cc,-0x77(%rcx)
7: 85 fd test %edi,%ebp
9: 4c 89 e1 mov %r12,%rcx
c: 4d 8b 36 mov (%r14),%r14
f: 49 39 ce cmp %rcx,%r14
12: 4d 8d a7 80 03 00 00 lea 0x380(%r15),%r12
19: 0f 84 9f 01 00 00 je 0x1be
1f: 49 8d 7e 70 lea 0x70(%r14),%rdi
23: 48 89 f8 mov %rdi,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 42 0f b6 04 28 movzbl (%rax,%r13,1),%eax <-- trapping instruction
2f: 84 c0 test %al,%al
31: 0f 85 83 03 00 00 jne 0x3ba
37: 45 8b 66 70 mov 0x70(%r14),%r12d
3b: 4c 89 75 c8 mov %r14,-0x38(%rbp)
3f: 49 rex.WB


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