[syzbot] [net?] general protection fault in rt6_insert_exception

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 66edb901bf87 Merge tag 'v7.1-p3' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15b40d06580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d0f0911eedbc130a
dashboard link: https://syzkaller.appspot.com/bug?extid=01f005f9c6387ca6f6dd
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
userspace arch: i386

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-66edb901.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8741b8f9dedf/vmlinux-66edb901.xz
kernel image: https://storage.googleapis.com/syzbot-assets/675ec9fff2a9/bzImage-66edb901.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+01f005...@syzkaller.appspotmail.com

kvm_intel: set kvm_intel.dump_invalid_vmcs=1 to dump internal KVM state.
Oops: general protection fault, probably for non-canonical address 0xdffffc00000000bc: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x00000000000005e0-0x00000000000005e7]
CPU: 0 UID: 0 PID: 7890 Comm: syz.2.502 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:fib6_mtu net/ipv6/route.c:1648 [inline]
RIP: 0010:rt6_insert_exception+0x9eb/0x10a0 net/ipv6/route.c:1753
Code: 3b 14 cf f7 45 85 f6 0f 85 1d 02 00 00 e8 7d 19 cf f7 48 8d bb e0 05 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 89
RSP: 0000:ffffc9000610f120 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffc9000c001000
RDX: 00000000000000bc RSI: ffffffff8a38bc83 RDI: 00000000000005e0
RBP: ffff888052f06000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff888042d16c00
R13: ffff888042d16cc8 R14: 0000000000000001 R15: 0000000000000500
FS: 0000000000000000(0000) GS:ffff88809717d000(0063) knlGS:00000000f540db40
CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00000000f73c6d50 CR3: 000000006eff0000 CR4: 0000000000352ef0
Call Trace:
<TASK>
__ip6_rt_update_pmtu+0x555/0xd60 net/ipv6/route.c:2982
ip6_update_pmtu+0x34f/0x3b0 net/ipv6/route.c:3014
icmpv6_err+0x2a2/0x3f0 net/ipv6/icmp.c:82
icmpv6_notify+0x35e/0x820 net/ipv6/icmp.c:1087
icmpv6_rcv+0x10bf/0x1ae0 net/ipv6/icmp.c:1228
ip6_protocol_deliver_rcu+0xf97/0x1500 net/ipv6/ip6_input.c:478
ip6_input_finish+0x1e4/0x4a0 net/ipv6/ip6_input.c:529
NF_HOOK include/linux/netfilter.h:318 [inline]
NF_HOOK include/linux/netfilter.h:312 [inline]
ip6_input+0x105/0x2f0 net/ipv6/ip6_input.c:540
ip6_mc_input+0x513/0xf50 net/ipv6/ip6_input.c:630
dst_input include/net/dst.h:480 [inline]
ip6_rcv_finish net/ipv6/ip6_input.c:119 [inline]
NF_HOOK include/linux/netfilter.h:318 [inline]
NF_HOOK include/linux/netfilter.h:312 [inline]
ipv6_rcv+0x34c/0x3d0 net/ipv6/ip6_input.c:351
__netif_receive_skb_one_core+0x12d/0x1e0 net/core/dev.c:6202
__netif_receive_skb+0x1f/0x120 net/core/dev.c:6315
netif_receive_skb_internal net/core/dev.c:6401 [inline]
netif_receive_skb+0x13b/0x7f0 net/core/dev.c:6460
tun_rx_batched.isra.0+0x3f6/0x750 drivers/net/tun.c:1511
tun_get_user+0x1e31/0x3c20 drivers/net/tun.c:1955
tun_chr_write_iter+0xdc/0x200 drivers/net/tun.c:2001
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1070 fs/read_write.c:688
ksys_write+0x12a/0x250 fs/read_write.c:740
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
do_int80_emulation+0x141/0x700 arch/x86/entry/syscall_32.c:172
asm_int80_emulation+0x1a/0x20 arch/x86/include/asm/idtentry.h:621
RIP: 0023:0xf715616b
Code: 57 56 53 8b 44 24 14 f6 00 08 75 23 8b 44 24 18 8b 5c 24 1c 8b 4c 24 20 8b 54 24 24 8b 74 24 28 8b 7c 24 2c 8b 6c 24 30 cd 80 <5b> 5e 5f 5d c3 5b 5e 5f 5d e9 f7 a1 ff ff 66 90 66 90 66 90 90 53
RSP: 002b:00000000f540d44c EFLAGS: 00000246 ORIG_RAX: 0000000000000004
RAX: ffffffffffffffda RBX: 00000000000000c8 RCX: 0000000080000640
RDX: 000000000000007a RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000292 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:fib6_mtu net/ipv6/route.c:1648 [inline]
RIP: 0010:rt6_insert_exception+0x9eb/0x10a0 net/ipv6/route.c:1753
Code: 3b 14 cf f7 45 85 f6 0f 85 1d 02 00 00 e8 7d 19 cf f7 48 8d bb e0 05 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 89
RSP: 0000:ffffc9000610f120 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffc9000c001000
RDX: 00000000000000bc RSI: ffffffff8a38bc83 RDI: 00000000000005e0
RBP: ffff888052f06000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff888042d16c00
R13: ffff888042d16cc8 R14: 0000000000000001 R15: 0000000000000500
FS: 0000000000000000(0000) GS:ffff88809717d000(0063) knlGS:00000000f540db40
CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00000000f73c6d50 CR3: 000000006eff0000 CR4: 0000000000352ef0
----------------
Code disassembly (best guess):
0: 3b 14 cf cmp (%rdi,%rcx,8),%edx
3: f7 45 85 f6 0f 85 1d testl $0x1d850ff6,-0x7b(%rbp)
a: 02 00 add (%rax),%al
c: 00 e8 add %ch,%al
e: 7d 19 jge 0x29
10: cf iret
11: f7 48 8d bb e0 05 00 testl $0x5e0bb,-0x73(%rax)
18: 00 48 b8 add %cl,-0x48(%rax)
1b: 00 00 add %al,(%rax)
1d: 00 00 add %al,(%rax)
1f: 00 fc add %bh,%ah
21: ff lcall (bad)
22: df 48 89 fisttps -0x77(%rax)
25: fa cli
26: 48 c1 ea 03 shr $0x3,%rdx
* 2a: 0f b6 14 02 movzbl (%rdx,%rax,1),%edx <-- trapping instruction
2e: 48 89 f8 mov %rdi,%rax
31: 83 e0 07 and $0x7,%eax
34: 83 c0 03 add $0x3,%eax
37: 38 d0 cmp %dl,%al
39: 7c 08 jl 0x43
3b: 84 d2 test %dl,%dl
3d: 0f .byte 0xf
3e: 85 .byte 0x85
3f: 89 .byte 0x89


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