Subject: Re: [PATCH net] ipv6: ip6_append_data_mtu did not care about pmtudisc and frag_size

From: Gao feng <[email-masked]>
Date: Tue, 02 Jul 2013 10:46:38 +0800

On 07/02/2013 02:17 AM, Hannes Frederic Sowa wrote:
> If the socket had an IPV6_MTU value set, ip6_append_data_mtu lost track
> of this when appending the second frame on a corked socket. This results
> in the following splat:
> 
> [37598.993962] ------------[ cut here ]------------
> [37598.994008] kernel BUG at net/core/skbuff.c:2064!
> [37598.994008] invalid opcode: 0000 [#1] SMP
> [37598.994008] Modules linked in: tcp_lp uvcvideo videobuf2_vmalloc videobuf2_memops videobuf2_core videodev media vfat fat usb_storage fuse ebtable_nat xt_CHECKSUM bridge stp llc ipt_MASQUERADE nf_conntrack_netbios_ns nf_conntrack_broadcast ip6table_mangle ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 iptable_nat
> +nf_nat_ipv4 nf_nat iptable_mangle nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ebtable_filter ebtables ip6table_filter ip6_tables be2iscsi iscsi_boot_sysfs bnx2i cnic uio cxgb4i cxgb4 cxgb3i cxgb3 mdio libcxgbi ib_iser rdma_cm ib_addr iw_cm ib_cm ib_sa ib_mad ib_core iscsi_tcp libiscsi_tcp libiscsi
> +scsi_transport_iscsi rfcomm bnep iTCO_wdt iTCO_vendor_support snd_hda_codec_conexant arc4 iwldvm mac80211 snd_hda_intel acpi_cpufreq mperf coretemp snd_hda_codec microcode cdc_wdm cdc_acm
> [37598.994008]  snd_hwdep cdc_ether snd_seq snd_seq_device usbnet mii joydev btusb snd_pcm bluetooth i2c_i801 e1000e lpc_ich mfd_core ptp iwlwifi pps_core snd_page_alloc mei cfg80211 snd_timer thinkpad_acpi snd tpm_tis soundcore rfkill tpm tpm_bios vhost_net tun macvtap macvlan kvm_intel kvm uinput binfmt_misc
> +dm_crypt i915 i2c_algo_bit drm_kms_helper drm i2c_core wmi video
> [37598.994008] CPU 0
> [37598.994008] Pid: 27320, comm: t2 Not tainted 3.9.6-200.fc18.x86_64 #1 LENOVO 27744PG/27744PG
> [37598.994008] RIP: 0010:[<ffffffff815443a5>]  [<ffffffff815443a5>] skb_copy_and_csum_bits+0x325/0x330
> [37598.994008] RSP: 0018:ffff88003670da18  EFLAGS: 00010202
> [37598.994008] RAX: ffff88018105c018 RBX: 0000000000000004 RCX: 00000000000006c0
> [37598.994008] RDX: ffff88018105a6c0 RSI: ffff88018105a000 RDI: ffff8801e1b0aa00
> [37598.994008] RBP: ffff88003670da78 R08: 0000000000000000 R09: ffff88018105c040
> [37598.994008] R10: ffff8801e1b0aa00 R11: 0000000000000000 R12: 000000000000fff8
> [37598.994008] R13: 00000000000004fc R14: 00000000ffff0504 R15: 0000000000000000
> [37598.994008] FS:  00007f28eea59740(0000) GS:ffff88023bc00000(0000) knlGS:0000000000000000
> [37598.994008] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [37598.994008] CR2: 0000003d935789e0 CR3: 00000000365cb000 CR4: 00000000000407f0
> [37598.994008] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [37598.994008] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [37598.994008] Process t2 (pid: 27320, threadinfo ffff88003670c000, task ffff88022c162ee0)
> [37598.994008] Stack:
> [37598.994008]  ffff88022e098a00 ffff88020f973fc0 0000000000000008 00000000000004c8
> [37598.994008]  ffff88020f973fc0 00000000000004c4 ffff88003670da78 ffff8801e1b0a200
> [37598.994008]  0000000000000018 00000000000004c8 ffff88020f973fc0 00000000000004c4
> [37598.994008] Call Trace:
> [37598.994008]  [<ffffffff815fc21f>] ip6_append_data+0xccf/0xfe0
> [37598.994008]  [<ffffffff8158d9f0>] ? ip_copy_metadata+0x1a0/0x1a0
> [37598.994008]  [<ffffffff81661f66>] ? _raw_spin_lock_bh+0x16/0x40
> [37598.994008]  [<ffffffff8161548d>] udpv6_sendmsg+0x1ed/0xc10
> [37598.994008]  [<ffffffff812a2845>] ? sock_has_perm+0x75/0x90
> [37598.994008]  [<ffffffff815c3693>] inet_sendmsg+0x63/0xb0
> [37598.994008]  [<ffffffff812a2973>] ? selinux_socket_sendmsg+0x23/0x30
> [37598.994008]  [<ffffffff8153a450>] sock_sendmsg+0xb0/0xe0
> [37598.994008]  [<ffffffff810135d1>] ? __switch_to+0x181/0x4a0
> [37598.994008]  [<ffffffff8153d97d>] sys_sendto+0x12d/0x180
> [37598.994008]  [<ffffffff810dfb64>] ? __audit_syscall_entry+0x94/0xf0
> [37598.994008]  [<ffffffff81020ed1>] ? syscall_trace_enter+0x231/0x240
> [37598.994008]  [<ffffffff8166a7e7>] tracesys+0xdd/0xe2
> [37598.994008] Code: fe 07 00 00 48 c7 c7 04 28 a6 81 89 45 a0 4c 89 4d b8 44 89 5d a8 e8 1b ac b1 ff 44 8b 5d a8 4c 8b 4d b8 8b 45 a0 e9 cf fe ff ff <0f> 0b 66 0f 1f 84 00 00 00 00 00 66 66 66 66 90 55 48 89 e5 48
> [37598.994008] RIP  [<ffffffff815443a5>] skb_copy_and_csum_bits+0x325/0x330
> [37598.994008]  RSP <ffff88003670da18>
> [37599.007323] ---[ end trace d69f6a17f8ac8eee ]---
> 
> While there, also check if path mtu discovery is activated for this
> socket. The logic was adapted from ip6_append_data when first writing
> on the corked socket.
> 
> This bug was introduced with commit
> 0c1833797a5a6ec23ea9261d979aa18078720b74 ("ipv6: fix incorrect ipsec
> fragment").
> 
> Cc: Gao feng <[email-masked]>
> Cc: YOSHIFUJI Hideaki <[email-masked]>
> Signed-off-by: Hannes Frederic Sowa <[email-masked]>
> ---
>  net/ipv6/ip6_output.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index dae1949..7701735 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -1097,7 +1097,8 @@ static void ip6_append_data_mtu(int *mtu,
>  				int *maxfraglen,
>  				unsigned int fragheaderlen,
>  				struct sk_buff *skb,
> -				struct rt6_info *rt)
> +				struct rt6_info *rt,
> +				struct ipv6_pinfo *np)
>  {
>  	if (!(rt->dst.flags & DST_XFRM_TUNNEL)) {
>  		if (skb == NULL) {
> @@ -1109,7 +1110,11 @@ static void ip6_append_data_mtu(int *mtu,
>  			 * this fragment is not first, the headers
>  			 * space is regarded as data space.
>  			 */
> -			*mtu = dst_mtu(rt->dst.path);
> +			*mtu = (np->pmtudisc == IPV6_PMTUDISC_DO) ?
> +				rt->dst.dev->mtu :
> +				dst_mtu(rt->dst.path);
> +			if (np->frag_size && np->frag_size < *mtu)
> +				*mtu = np->frag_size;

No need to pass ipv6_pinfo to ip6_append_data_mtu, the below is enough.

*mtu = min(*mtu, (np->pmtudisc == IPV6_PMTUDISC_DO) ?
				rt->dst.dev->mtu :
				dst_mtu(rt->dst.path);

This patch looks good go me.

Acked-by: Gao feng <[email-masked]>

Thanks!
>  		}
>  		*maxfraglen = ((*mtu - fragheaderlen) & ~7)
>  			      + fragheaderlen - sizeof(struct frag_hdr);
> @@ -1287,8 +1292,7 @@ alloc_new_skb:
>  			/* update mtu and maxfraglen if necessary */
>  			if (skb == NULL || skb_prev == NULL)
>  				ip6_append_data_mtu(&mtu, &maxfraglen,
> -						    fragheaderlen, skb, rt);
> -
> +						    fragheaderlen, skb, rt, np);
>  			skb_prev = skb;
>  
>  			/*
>