Subject: [syzbot] [bpf?] [net?] general protection fault in xdp_do_redirect

From: syzbot <[email-masked]>
Date: Mon, 01 Jul 2024 16:53:19 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    642a16ca7994 Add linux-next specific files for 20240627
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=147914c6980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ba15715f73169384
dashboard link: https://syzkaller.appspot.com/bug?extid=0b5c75599f1d872bea6f
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/72ed10c6e9be/disk-642a16ca.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f2ca81ede1c4/vmlinux-642a16ca.xz
kernel image: https://storage.googleapis.com/syzbot-assets/af14c94fa854/bzImage-642a16ca.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000007: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f]
CPU: 0 UID: 60928 PID: 8680 Comm: syz.1.877 Not tainted 6.10.0-rc5-next-20240627-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
RIP: 0010:bpf_net_ctx_get_ri include/linux/filter.h:788 [inline]
RIP: 0010:xdp_do_redirect+0x63/0xb40 net/core/filter.c:4423
Code: c3 08 18 00 00 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 ec 04 91 f8 4c 8b 23 4d 8d 74 24 38 4c 89 f3 48 c1 eb 03 <42> 0f b6 04 2b 84 c0 0f 85 fc 07 00 00 41 8b 2e 89 ee 83 e6 02 31
RSP: 0018:ffffc9001600f828 EFLAGS: 00010202
RAX: 1ffff110033f1301 RBX: 0000000000000007 RCX: 0000000000040000
RDX: ffffc9000ac74000 RSI: 0000000000000204 RDI: 0000000000000205
RBP: ffffc9001600f9b0 R08: 0000000000000005 R09: ffffffff866b25e9
R10: 0000000000000005 R11: ffff888019f88000 R12: 0000000000000000
R13: dffffc0000000000 R14: 0000000000000038 R15: ffffc9001600faf0
FS:  00007fe5bc2366c0(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2411f23000 CR3: 000000005d692000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 tun_xdp_act+0xe9/0xb70 drivers/net/tun.c:1626
 tun_build_skb drivers/net/tun.c:1716 [inline]
 tun_get_user+0x346d/0x4560 drivers/net/tun.c:1819
 tun_chr_write_iter+0x113/0x1f0 drivers/net/tun.c:2048
 new_sync_write fs/read_write.c:497 [inline]
 vfs_write+0xa72/0xc90 fs/read_write.c:590
 ksys_write+0x1a0/0x2c0 fs/read_write.c:643
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe5bb3746df
Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 f9 8b 02 00 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 4c 8c 02 00 48
RSP: 002b:00007fe5bc236010 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fe5bb503fa0 RCX: 00007fe5bb3746df
RDX: 000000000000003e RSI: 0000000020000280 RDI: 00000000000000c8
RBP: 00007fe5bb3f6756 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000003e R11: 0000000000000293 R12: 0000000000000000
R13: 000000000000000b R14: 00007fe5bb503fa0 R15: 00007ffe2c314948
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:bpf_net_ctx_get_ri include/linux/filter.h:788 [inline]
RIP: 0010:xdp_do_redirect+0x63/0xb40 net/core/filter.c:4423
Code: c3 08 18 00 00 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 ec 04 91 f8 4c 8b 23 4d 8d 74 24 38 4c 89 f3 48 c1 eb 03 <42> 0f b6 04 2b 84 c0 0f 85 fc 07 00 00 41 8b 2e 89 ee 83 e6 02 31
RSP: 0018:ffffc9001600f828 EFLAGS: 00010202
RAX: 1ffff110033f1301 RBX: 0000000000000007 RCX: 0000000000040000
RDX: ffffc9000ac74000 RSI: 0000000000000204 RDI: 0000000000000205
RBP: ffffc9001600f9b0 R08: 0000000000000005 R09: ffffffff866b25e9
R10: 0000000000000005 R11: ffff888019f88000 R12: 0000000000000000
R13: dffffc0000000000 R14: 0000000000000038 R15: ffffc9001600faf0
FS:  00007fe5bc2366c0(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2411f23000 CR3: 000000005d692000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	c3                   	ret
   1:	08 18                	or     %bl,(%rax)
   3:	00 00                	add    %al,(%rax)
   5:	48 89 d8             	mov    %rbx,%rax
   8:	48 c1 e8 03          	shr    $0x3,%rax
   c:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1)
  11:	74 08                	je     0x1b
  13:	48 89 df             	mov    %rbx,%rdi
  16:	e8 ec 04 91 f8       	call   0xf8910507
  1b:	4c 8b 23             	mov    (%rbx),%r12
  1e:	4d 8d 74 24 38       	lea    0x38(%r12),%r14
  23:	4c 89 f3             	mov    %r14,%rbx
  26:	48 c1 eb 03          	shr    $0x3,%rbx
* 2a:	42 0f b6 04 2b       	movzbl (%rbx,%r13,1),%eax <-- trapping instruction
  2f:	84 c0                	test   %al,%al
  31:	0f 85 fc 07 00 00    	jne    0x833
  37:	41 8b 2e             	mov    (%r14),%ebp
  3a:	89 ee                	mov    %ebp,%esi
  3c:	83 e6 02             	and    $0x2,%esi
  3f:	31                   	.byte 0x31

---
This report 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 [email-masked].

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup