Wang Liang wrote:
> When sending a packet with virtio_net_hdr to tun device, if the gso_type
> in virtio_net_hdr is SKB_GSO_UDP and the gso_size is less than udphdr
> size, below crash may happen.
>
> ------------[ cut here ]------------
> kernel BUG at net/core/skbuff.c:4572!
The BUG_ON hit:
void *skb_pull_rcsum(struct sk_buff *skb, unsigned int len)
{
unsigned char *data = skb->data;
BUG_ON(len > skb->len);
> Oops: invalid opcode: 0000 [#1] SMP NOPTI
> CPU: 0 UID: 0 PID: 62 Comm: mytest Not tainted 6.16.0-rc7 #203
> PREEMPT(voluntary)
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1
> 04/01/2014
> RIP: 0010:skb_pull_rcsum+0x8e/0xa0
>From udp_csum_pull_header
> Code: 00 00 5b c3 cc cc cc cc 8b 93 88 00 00 00 f7 da e8 37 44 38 00 f7 d8
> 89 83 88 00 00 00 48 8b 83 c8 00 00 00 5b c3 cc cc cc cc <0f> 0b 0f 0b 66 66
> 2e 0f 1f 84 00 000
> RSP: 0018:ffffc900001fba38 EFLAGS: 00000297
> RAX: 0000000000000004 RBX: ffff8880040c1000 RCX: ffffc900001fb948
> RDX: ffff888003e6d700 RSI: 0000000000000008 RDI: ffff88800411a062
> RBP: ffff8880040c1000 R08: 0000000000000000 R09: 0000000000000001
> R10: ffff888003606c00 R11: 0000000000000001 R12: 0000000000000000
> R13: ffff888004060900 R14: ffff888004050000 R15: ffff888004060900
> FS: 000000002406d3c0(0000) GS:ffff888084a19000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020000040 CR3: 0000000004007000 CR4: 00000000000006f0
> Call Trace:
> <TASK>
> udp_queue_rcv_one_skb+0x176/0x4b0 net/ipv4/udp.c:2445
> udp_queue_rcv_skb+0x155/0x1f0 net/ipv4/udp.c:2475
> udp_unicast_rcv_skb+0x71/0x90 net/ipv4/udp.c:2626
> __udp4_lib_rcv+0x433/0xb00 net/ipv4/udp.c:2690
> ip_protocol_deliver_rcu+0xa6/0x160 net/ipv4/ip_input.c:205
> ip_local_deliver_finish+0x72/0x90 net/ipv4/ip_input.c:233
> ip_sublist_rcv_finish+0x5f/0x70 net/ipv4/ip_input.c:579
> ip_sublist_rcv+0x122/0x1b0 net/ipv4/ip_input.c:636
> ip_list_rcv+0xf7/0x130 net/ipv4/ip_input.c:670
> __netif_receive_skb_list_core+0x21d/0x240 net/core/dev.c:6067
> netif_receive_skb_list_internal+0x186/0x2b0 net/core/dev.c:6210
> napi_complete_done+0x78/0x180 net/core/dev.c:6580
> tun_get_user+0xa63/0x1120 drivers/net/tun.c:1909
> tun_chr_write_iter+0x65/0xb0 drivers/net/tun.c:1984
> vfs_write+0x300/0x420 fs/read_write.c:593
> ksys_write+0x60/0xd0 fs/read_write.c:686
> do_syscall_64+0x50/0x1c0 arch/x86/entry/syscall_64.c:63
> </TASK>
>
> To trigger gso segment in udp_queue_rcv_skb(), we should also set option
> UDP_ENCAP_ESPINUDP to enable udp_sk(sk)->encap_rcv. When the encap_rcv
> hook return 1 in udp_queue_rcv_one_skb(), udp_csum_pull_header() will try
> to pull udphdr, but the skb size has been segmented to gso size, which
> leads to this crash.
>
> Only udp has this probloem. Add check for the minimum value of gso size in
> virtio_net_hdr_to_skb().
>
> Fixes: cf329aa42b66 ("udp: cope with UDP GRO packet misdirection")
> Fixes: 3d010c8031e3 ("udp: do not accept non-tunnel GSO skbs landing in a
> tunnel")
> Signed-off-by: Wang Liang <wanglian...@huawei.com>
> ---
> include/linux/virtio_net.h | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
> index 02a9f4dc594d..0533101642bd 100644
> --- a/include/linux/virtio_net.h
> +++ b/include/linux/virtio_net.h
> @@ -157,11 +157,13 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff
> *skb,
> u16 gso_size = __virtio16_to_cpu(little_endian, hdr->gso_size);
> unsigned int nh_off = p_off;
> struct skb_shared_info *shinfo = skb_shinfo(skb);
> + u16 min_gso_size = 0;
>
> switch (gso_type & ~SKB_GSO_TCP_ECN) {
> case SKB_GSO_UDP:
> /* UFO may not include transport header in gso_size. */
> nh_off -= thlen;
> + min_gso_size = sizeof(struct udphdr) + 1;
> break;
> case SKB_GSO_UDP_L4:
> if (!(hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM))
> @@ -172,6 +174,7 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff
> *skb,
> return -EINVAL;
> if (gso_type != SKB_GSO_UDP_L4)
> return -EINVAL;
> + min_gso_size = sizeof(struct udphdr) + 1;
> break;
> case SKB_GSO_TCPV4:
> case SKB_GSO_TCPV6:
> @@ -182,7 +185,7 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff
> *skb,
> }
>
> /* Kernel has a special handling for GSO_BY_FRAGS. */
> - if (gso_size == GSO_BY_FRAGS)
> + if ((gso_size == GSO_BY_FRAGS) || (gso_size < min_gso_size))
gso_size is the size of the segment payload, excluding the transport
header.
This is probably not the right approach.
Not sure how a GSO skb can be built that is shorter than even the
transport header. Maybe an skb_dump of the GSO skb can be elucidating.
> return -EINVAL;
>
> /* Too small packets are not really GSO ones. */
> --
> 2.34.1
>
