Re: [syzbot] general protection fault in sock_from_file

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    93717cde744f Add linux-next specific files for 20210830
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15200fad300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c643ef5289990dd1
dashboard link: https://syzkaller.appspot.com/bug?extid=f9704d1878e290eddf73
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=111f5f9d300000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1651a415300000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f9704d1878e290eddf73@xxxxxxxxxxxxxxxxxxxxxxxxx

general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
CPU: 0 PID: 6548 Comm: syz-executor433 Not tainted 5.14.0-next-20210830-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:sock_from_file+0x20/0x90 net/socket.c:505
Code: f5 ff ff ff c3 0f 1f 44 00 00 41 54 53 48 89 fb e8 85 e9 62 fa 48 8d 7b 28 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 4f 45 31 e4 48 81 7b 28 80 f1 8a 8a 74 0c e8 58 e9
RSP: 0018:ffffc90002caf8e8 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000005 RSI: ffffffff8713203b RDI: 0000000000000028
RBP: ffff888019fc0780 R08: ffffffff899aee40 R09: ffffffff81e21978
R10: 0000000000000027 R11: 0000000000000009 R12: dffffc0000000000
R13: 1ffff110033f80f9 R14: 0000000000000003 R15: ffff888019fc0780
FS:  00000000013b5300(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004ae0f0 CR3: 000000001d355000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 io_sendmsg+0x98/0x640 fs/io_uring.c:4681
 io_issue_sqe+0x14de/0x6ba0 fs/io_uring.c:6578
 __io_queue_sqe+0x90/0xb50 fs/io_uring.c:6864
 io_req_task_submit+0xbf/0x1b0 fs/io_uring.c:2218
 tctx_task_work+0x166/0x610 fs/io_uring.c:2143
 task_work_run+0xdd/0x1a0 kernel/task_work.c:164
 tracehook_notify_signal include/linux/tracehook.h:212 [inline]
 handle_signal_work kernel/entry/common.c:146 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
 exit_to_user_mode_prepare+0x256/0x290 kernel/entry/common.c:209
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:302
 do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x43fd49
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 14 00 00 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 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd6347b9d8 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
RAX: 0000000000001000 RBX: 0000000000000003 RCX: 000000000043fd49
RDX: 0000000000000000 RSI: 000000000000688c RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004035d0
R13: 431bde82d7b634db R14: 00000000004ae018 R15: 0000000000400488
Modules linked in:
---[ end trace aa9bf60339277d03 ]---
RIP: 0010:sock_from_file+0x20/0x90 net/socket.c:505
Code: f5 ff ff ff c3 0f 1f 44 00 00 41 54 53 48 89 fb e8 85 e9 62 fa 48 8d 7b 28 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 4f 45 31 e4 48 81 7b 28 80 f1 8a 8a 74 0c e8 58 e9
RSP: 0018:ffffc90002caf8e8 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000005 RSI: ffffffff8713203b RDI: 0000000000000028
RBP: ffff888019fc0780 R08: ffffffff899aee40 R09: ffffffff81e21978
R10: 0000000000000027 R11: 0000000000000009 R12: dffffc0000000000
R13: 1ffff110033f80f9 R14: 0000000000000003 R15: ffff888019fc0780
FS:  00000000013b5300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2cc6f84000 CR3: 000000001d355000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess), 3 bytes skipped:
   0:	ff c3                	inc    %ebx
   2:	0f 1f 44 00 00       	nopl   0x0(%rax,%rax,1)
   7:	41 54                	push   %r12
   9:	53                   	push   %rbx
   a:	48 89 fb             	mov    %rdi,%rbx
   d:	e8 85 e9 62 fa       	callq  0xfa62e997
  12:	48 8d 7b 28          	lea    0x28(%rbx),%rdi
  16:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  1d:	fc ff df
  20:	48 89 fa             	mov    %rdi,%rdx
  23:	48 c1 ea 03          	shr    $0x3,%rdx
* 27:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1) <-- trapping instruction
  2b:	75 4f                	jne    0x7c
  2d:	45 31 e4             	xor    %r12d,%r12d
  30:	48 81 7b 28 80 f1 8a 	cmpq   $0xffffffff8a8af180,0x28(%rbx)
  37:	8a
  38:	74 0c                	je     0x46
  3a:	e8                   	.byte 0xe8
  3b:	58                   	pop    %rax
  3c:	e9                   	.byte 0xe9