[PATCH] ip6_offload: check segs for NULL in ipv6_gso_segment.

From: Artem Savkov
Date: Thu Dec 01 2016 - 08:06:33 EST

segs needs to be checked for being NULL in ipv6_gso_segment() before calling
skb_shinfo(segs), otherwise kernel can run into a NULL-pointer dereference:

[ 97.811262] BUG: unable to handle kernel NULL pointer dereference at 00000000000000cc
[ 97.819112] IP: [<ffffffff816e52f9>] ipv6_gso_segment+0x119/0x2f0
[ 97.825214] PGD 0 [ 97.827047]
[ 97.828540] Oops: 0000 [#1] SMP
[ 97.831678] Modules linked in: vhost_net vhost macvtap macvlan nfsv3 rpcsec_gss_krb5
nfsv4 dns_resolver nfs fscache xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4
iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack
ipt_REJECT nf_reject_ipv4 tun ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter
bridge stp llc snd_hda_codec_realtek snd_hda_codec_hdmi snd_hda_codec_generic snd_hda_intel
snd_hda_codec edac_mce_amd snd_hda_core edac_core snd_hwdep kvm_amd snd_seq kvm snd_seq_device
snd_pcm irqbypass snd_timer ppdev parport_serial snd parport_pc k10temp pcspkr soundcore parport
sp5100_tco shpchp sg wmi i2c_piix4 acpi_cpufreq nfsd auth_rpcgss nfs_acl lockd grace sunrpc
ip_tables xfs libcrc32c sr_mod cdrom sd_mod ata_generic pata_acpi amdkfd amd_iommu_v2 radeon
broadcom bcm_phy_lib i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops
ttm ahci serio_raw tg3 firewire_ohci libahci pata_atiixp drm ptp libata firewire_core pps_core
i2c_core crc_itu_t fjes dm_mirror dm_region_hash dm_log dm_mod
[ 97.927721] CPU: 1 PID: 3504 Comm: vhost-3495 Not tainted 4.9.0-7.el7.test.x86_64 #1
[ 97.935457] Hardware name: AMD Snook/Snook, BIOS ESK0726A 07/26/2010
[ 97.941806] task: ffff880129a1c080 task.stack: ffffc90001bcc000
[ 97.947720] RIP: 0010:[<ffffffff816e52f9>] [<ffffffff816e52f9>] ipv6_gso_segment+0x119/0x2f0
[ 97.956251] RSP: 0018:ffff88012fc43a10 EFLAGS: 00010207
[ 97.961557] RAX: 0000000000000000 RBX: ffff8801292c8700 RCX: 0000000000000594
[ 97.968687] RDX: 0000000000000593 RSI: ffff880129a846c0 RDI: 0000000000240000
[ 97.975814] RBP: ffff88012fc43a68 R08: ffff880129a8404e R09: 0000000000000000
[ 97.982942] R10: 0000000000000000 R11: ffff880129a84076 R12: 00000020002949b3
[ 97.990070] R13: ffff88012a580000 R14: 0000000000000000 R15: ffff88012a580000
[ 97.997198] FS: 0000000000000000(0000) GS:ffff88012fc40000(0000) knlGS:0000000000000000
[ 98.005280] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 98.011021] CR2: 00000000000000cc CR3: 0000000126c5d000 CR4: 00000000000006e0
[ 98.018149] Stack:
[ 98.020157] 00000000ffffffff ffff88012fc43ac8 ffffffffa017ad0a 000000000000000e
[ 98.027584] 0000001300000000 0000000077d59998 ffff8801292c8700 00000020002949b3
[ 98.035010] ffff88012a580000 0000000000000000 ffff88012a580000 ffff88012fc43a98
[ 98.042437] Call Trace:
[ 98.044879] <IRQ> [ 98.046803] [<ffffffffa017ad0a>] ? tg3_start_xmit+0x84a/0xd60 [tg3]
[ 98.053156] [<ffffffff815eeee0>] skb_mac_gso_segment+0xb0/0x130
[ 98.059158] [<ffffffff815eefd3>] __skb_gso_segment+0x73/0x110
[ 98.064985] [<ffffffff815ef40d>] validate_xmit_skb+0x12d/0x2b0
[ 98.070899] [<ffffffff815ef5d2>] validate_xmit_skb_list+0x42/0x70
[ 98.077073] [<ffffffff81618560>] sch_direct_xmit+0xd0/0x1b0
[ 98.082726] [<ffffffff815efd86>] __dev_queue_xmit+0x486/0x690
[ 98.088554] [<ffffffff8135c135>] ? cpumask_next_and+0x35/0x50
[ 98.094380] [<ffffffff815effa0>] dev_queue_xmit+0x10/0x20
[ 98.099863] [<ffffffffa09ce057>] br_dev_queue_push_xmit+0xa7/0x170 [bridge]
[ 98.106907] [<ffffffffa09ce161>] br_forward_finish+0x41/0xc0 [bridge]
[ 98.113430] [<ffffffff81627cf2>] ? nf_iterate+0x52/0x60
[ 98.118735] [<ffffffff81627d6b>] ? nf_hook_slow+0x6b/0xc0
[ 98.124216] [<ffffffffa09ce32c>] __br_forward+0x14c/0x1e0 [bridge]
[ 98.130480] [<ffffffffa09ce120>] ? br_dev_queue_push_xmit+0x170/0x170 [bridge]
[ 98.137785] [<ffffffffa09ce4bd>] br_forward+0x9d/0xb0 [bridge]
[ 98.143701] [<ffffffffa09cfbb7>] br_handle_frame_finish+0x267/0x560 [bridge]
[ 98.150834] [<ffffffffa09d0064>] br_handle_frame+0x174/0x2f0 [bridge]
[ 98.157355] [<ffffffff8102fb89>] ? sched_clock+0x9/0x10
[ 98.162662] [<ffffffff810b63b2>] ? sched_clock_cpu+0x72/0xa0
[ 98.168403] [<ffffffff815eccf5>] __netif_receive_skb_core+0x1e5/0xa20
[ 98.174926] [<ffffffff813659f9>] ? timerqueue_add+0x59/0xb0
[ 98.180580] [<ffffffff815ed548>] __netif_receive_skb+0x18/0x60
[ 98.186494] [<ffffffff815ee625>] process_backlog+0x95/0x140
[ 98.192145] [<ffffffff815edccd>] net_rx_action+0x16d/0x380
[ 98.197713] [<ffffffff8170cff1>] __do_softirq+0xd1/0x283
[ 98.203106] [<ffffffff8170b2bc>] do_softirq_own_stack+0x1c/0x30
[ 98.209107] <EOI> [ 98.211029] [<ffffffff8108a5c0>] do_softirq+0x50/0x60
[ 98.216166] [<ffffffff815ec853>] netif_rx_ni+0x33/0x80
[ 98.221386] [<ffffffffa09eeff7>] tun_get_user+0x487/0x7f0 [tun]
[ 98.227388] [<ffffffffa09ef3ab>] tun_sendmsg+0x4b/0x60 [tun]
[ 98.233129] [<ffffffffa0b68932>] handle_tx+0x282/0x540 [vhost_net]
[ 98.239392] [<ffffffffa0b68c25>] handle_tx_kick+0x15/0x20 [vhost_net]
[ 98.245916] [<ffffffffa0abacfe>] vhost_worker+0x9e/0xf0 [vhost]
[ 98.251919] [<ffffffffa0abac60>] ? vhost_umem_alloc+0x40/0x40 [vhost]
[ 98.258440] [<ffffffff81003a47>] ? do_syscall_64+0x67/0x180
[ 98.264094] [<ffffffff810a44d9>] kthread+0xd9/0xf0
[ 98.268965] [<ffffffff810a4400>] ? kthread_park+0x60/0x60
[ 98.274444] [<ffffffff8170a4d5>] ret_from_fork+0x25/0x30
[ 98.279836] Code: 8b 93 d8 00 00 00 48 2b 93 d0 00 00 00 4c 89 e6 48 89 df 66 89 93 c2 00 00 00 ff 10 48 3d 00 f0 ff ff 49 89 c2 0f 87 52 01 00 00 <41> 8b 92 cc 00 00 00 48 8b 80 d0 00 00 00 44 0f b7 74 10 06 66
[ 98.299425] RIP [<ffffffff816e52f9>] ipv6_gso_segment+0x119/0x2f0
[ 98.305612] RSP <ffff88012fc43a10>
[ 98.309094] CR2: 00000000000000cc
[ 98.312406] ---[ end trace 726a2c7a2d2d78d0 ]---

Signed-off-by: Artem Savkov <asavkov@xxxxxxxxxx>
---
net/ipv6/ip6_offload.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
index 1fcf61f..89c59e6 100644
--- a/net/ipv6/ip6_offload.c
+++ b/net/ipv6/ip6_offload.c
@@ -99,7 +99,7 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
segs = ops->callbacks.gso_segment(skb, features);
}

- if (IS_ERR(segs))
+ if (IS_ERR_OR_NULL(segs))
goto out;

gso_partial = !!(skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL);
--
2.7.4