Re: kernel BUG in fou_build_udp

[Eric Dumazet]

On Sat, Apr 15, 2023 at 9:44 PM Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> wrote:
>
> Hi,
>
> Thanks for reporting the issue.
>
> From:   Palash Oswal <oswalpalash@xxxxxxxxx>
> Date:   Thu, 13 Apr 2023 20:35:52 -0700
> > Hello,
> > I found the following issue using syzkaller with enriched corpus on:
> > HEAD commit : 0bcc4025550403ae28d2984bddacafbca0a2f112
> > git tree: linux
> >
> > C Reproducer : https://gist.github.com/oswalpalash/2a4bdb639c605ec80dbeec220e09603c
> > Kernel .config :
> > https://gist.github.com/oswalpalash/d9580b0bfce202b37445fa5fd426e41f
> > syz-repro :
> > r0 = socket$inet6(0xa, 0x2, 0x0)
> > r1 = socket$nl_route(0x10, 0x3, 0x0)
> > r2 = socket(0x10, 0x803, 0x0)
> > sendmsg$nl_route(r2, &(0x7f0000000380)={0x0, 0x0,
> > &(0x7f0000000340)={0x0, 0x14}}, 0x0)
> > getsockname$packet(r2, &(0x7f0000000100)={0x11, 0x0, <r3=>0x0, 0x1,
> > 0x0, 0x6, @broadcast}, &(0x7f00000000c0)=0x14)
> > sendmsg$nl_route(r1, &(0x7f0000000080)={0x0, 0x0,
> > &(0x7f0000000500)={&(0x7f0000000180)=@newlink={0x60, 0x10, 0x439, 0x0,
> > 0x0, {0x0, 0x0, 0x0, 0x0, 0x9801}, [@IFLA_LINKINFO={0x40, 0x12, 0x0,
> > 0x1, @sit={{0x8}, {0x34, 0x2, 0x0, 0x1, [@IFLA_IPTUN_LINK={0x8, 0x1,
> > r3}, @IFLA_IPTUN_ENCAP_TYPE={0x6, 0xf, 0x2},
> > @IFLA_IPTUN_ENCAP_SPORT={0x6, 0x11, 0x4e21},
> > @IFLA_IPTUN_ENCAP_SPORT={0x6, 0x11, 0x4e24}, @IFLA_IPTUN_LOCAL={0x8,
> > 0x2, @dev={0xac, 0x14, 0x14, 0x16}}, @IFLA_IPTUN_ENCAP_FLAGS={0x6,
> > 0x10, 0xfff}]}}}]}, 0x60}}, 0x20048894)
> > sendmmsg$inet(r0, &(0x7f00000017c0)=[{{&(0x7f0000000040)={0x2, 0x4e20,
> > @multicast1}, 0x10, 0x0, 0x0, &(0x7f0000000000)=[@ip_pktinfo={{0x1c,
> > 0x0, 0x8, {r3, @empty, @remote}}}], 0x20}}], 0x1, 0x0)
> >
> >
> > Console log:
> >
> > skbuff: skb_under_panic: text:ffffffff88a09da0 len:48 put:8
> > head:ffff88801e4be680 data:ffff88801e4be67c tail:0x2c end:0x140
> > dev:sit1
> > ------------[ cut here ]------------
> > kernel BUG at net/core/skbuff.c:150!
> > invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> > CPU: 0 PID: 10068 Comm: syz-executor.3 Not tainted
> > 6.3.0-rc6-pasta-00035-g0bcc40255504 #1
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> > 1.13.0-1ubuntu1.1 04/01/2014
> > RIP: 0010:skb_panic+0x152/0x1d0
> > Code: 0f b6 04 01 84 c0 74 04 3c 03 7e 20 8b 4b 70 41 56 45 89 e8 48
> > c7 c7 80 b3 5b 8b 41 57 56 48 89 ee 52 4c 89 e2 e8 ae 15 6c f9 <0f> 0b
> > 4c 89 4c 24 10 48 89 54 24 08 48 89 34 24 e8 69 1f d8 f9 4c
> > RSP: 0018:ffffc900029bead0 EFLAGS: 00010282
> > RAX: 0000000000000084 RBX: ffff88801d1c3d00 RCX: ffffc9000d863000
> > RDX: 0000000000000000 RSI: ffffffff816695cc RDI: 0000000000000005
> > RBP: ffffffff8b5bc1e0 R08: 0000000000000005 R09: 0000000000000000
> > R10: 0000000000000400 R11: 0000000000000000 R12: ffffffff88a09da0
> > R13: 0000000000000008 R14: ffff8880306b8000 R15: 0000000000000140
> > FS:  00007f1dae5ed700(0000) GS:ffff888063a00000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000564f403b7d10 CR3: 0000000117f1c000 CR4: 00000000000006f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >  <TASK>
> >  skb_push+0xc8/0xe0
> >  fou_build_udp+0x30/0x370
>
> It seems we need skb_cow_head() before skb_push().
> I'll take a deeper look on the repro.

Not sure about that.

The issue looks to be a lack of dev->needed_headroom update as we do
in other tunnels.

>
> ---8<---
> diff --git a/net/ipv4/fou_core.c b/net/ipv4/fou_core.c
> index cafec9b4eee0..24c751f1dbc4 100644
> --- a/net/ipv4/fou_core.c
> +++ b/net/ipv4/fou_core.c
> @@ -1013,10 +1013,15 @@ EXPORT_SYMBOL(__gue_build_header);
>
>  #ifdef CONFIG_NET_FOU_IP_TUNNELS
>
> -static void fou_build_udp(struct sk_buff *skb, struct ip_tunnel_encap *e,
> -                         struct flowi4 *fl4, u8 *protocol, __be16 sport)
> +static int fou_build_udp(struct sk_buff *skb, struct ip_tunnel_encap *e,
> +                        struct flowi4 *fl4, u8 *protocol, __be16 sport)
>  {
>         struct udphdr *uh;
> +       int err;
> +
> +       err = skb_cow_head(skb, sizeof(*uh));
> +       if (err)
> +               return err;
>
>         skb_push(skb, sizeof(struct udphdr));
>         skb_reset_transport_header(skb);
> @@ -1030,6 +1035,8 @@ static void fou_build_udp(struct sk_buff *skb, struct ip_tunnel_encap *e,
>                      fl4->saddr, fl4->daddr, skb->len);
>
>         *protocol = IPPROTO_UDP;
> +
> +       return 0;
>  }
>
>  static int fou_build_header(struct sk_buff *skb, struct ip_tunnel_encap *e,
> @@ -1044,9 +1051,7 @@ static int fou_build_header(struct sk_buff *skb, struct ip_tunnel_encap *e,
>         if (err)
>                 return err;
>
> -       fou_build_udp(skb, e, fl4, protocol, sport);
> -
> -       return 0;
> +       return fou_build_udp(skb, e, fl4, protocol, sport);
>  }
>
>  static int gue_build_header(struct sk_buff *skb, struct ip_tunnel_encap *e,
> @@ -1061,9 +1066,7 @@ static int gue_build_header(struct sk_buff *skb, struct ip_tunnel_encap *e,
>         if (err)
>                 return err;
>
> -       fou_build_udp(skb, e, fl4, protocol, sport);
> -
> -       return 0;
> +       return fou_build_udp(skb, e, fl4, protocol, sport);
>  }
>
>  static int gue_err_proto_handler(int proto, struct sk_buff *skb, u32 info)
> ---8<---
>
> Thanks,
> Kuniyuki
>
>
> >  gue_build_header+0xfb/0x150
> >  ip_tunnel_xmit+0x66e/0x3150
> >  sit_tunnel_xmit__.isra.0+0xe7/0x150
> >  sit_tunnel_xmit+0xf7e/0x28e0
> >  dev_hard_start_xmit+0x187/0x700
> >  __dev_queue_xmit+0x2ce4/0x3c40
> >  neigh_connected_output+0x3c2/0x550
> >  ip_finish_output2+0x78a/0x22e0
> >  __ip_finish_output+0x396/0x650
> >  ip_finish_output+0x31/0x280
> >  ip_mc_output+0x21f/0x710
> >  ip_send_skb+0xd8/0x260
> >  udp_send_skb+0x73a/0x1480
> >  udp_sendmsg+0x1bb2/0x2840
> >  udpv6_sendmsg+0x1710/0x2c20
> >  inet6_sendmsg+0x9d/0xe0
> >  sock_sendmsg+0xde/0x190
> >  ____sys_sendmsg+0x334/0x900
> >  ___sys_sendmsg+0x110/0x1b0
> >  __sys_sendmmsg+0x18f/0x460
> >  __x64_sys_sendmmsg+0x9d/0x100
> >  do_syscall_64+0x39/0xb0
> >  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > RIP: 0033:0x7f1dad88eacd
> > Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 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:00007f1dae5ecbf8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
> > RAX: ffffffffffffffda RBX: 00007f1dad9bbf80 RCX: 00007f1dad88eacd
> > RDX: 0000000000000001 RSI: 00000000200017c0 RDI: 0000000000000003
> > RBP: 00007f1dad8fcb05 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> > R13: 00007fff4922802f R14: 00007fff492281d0 R15: 00007f1dae5ecd80
> >  </TASK>
> > Modules linked in:
> > ---[ end trace 0000000000000000 ]---
> > RIP: 0010:skb_panic+0x152/0x1d0
> > Code: 0f b6 04 01 84 c0 74 04 3c 03 7e 20 8b 4b 70 41 56 45 89 e8 48
> > c7 c7 80 b3 5b 8b 41 57 56 48 89 ee 52 4c 89 e2 e8 ae 15 6c f9 <0f> 0b
> > 4c 89 4c 24 10 48 89 54 24 08 48 89 34 24 e8 69 1f d8 f9 4c
> > RSP: 0018:ffffc900029bead0 EFLAGS: 00010282
> > RAX: 0000000000000084 RBX: ffff88801d1c3d00 RCX: ffffc9000d863000
> > RDX: 0000000000000000 RSI: ffffffff816695cc RDI: 0000000000000005
> > RBP: ffffffff8b5bc1e0 R08: 0000000000000005 R09: 0000000000000000
> > R10: 0000000000000400 R11: 0000000000000000 R12: ffffffff88a09da0
> > R13: 0000000000000008 R14: ffff8880306b8000 R15: 0000000000000140
> > FS:  00007f1dae5ed700(0000) GS:ffff888063a00000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000564f403b7d10 CR3: 0000000117f1c000 CR4: 00000000000006f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400