bpf, testing: Introduce 'gso_linear_no_head_frag' skb_segment test

Following reports of skb_segment() hitting a BUG_ON when working on
GROed skbs which have their gso_size mangled (e.g. after a
bpf_skb_change_proto call), add a reproducer test that mimics the
input skbs that lead to the mentioned BUG_ON as in [1] and validates the
fix submitted in [2].

[1] https://lists.openwall.net/netdev/2019/08/26/110
[2] commit 3dcbdb134f32 ("net: gso: Fix skb_segment splat when splitting gso_size mangled skb having linear-headed frag_list")

Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20191025134223.2761-3-shmulik.ladkani@gmail.com

diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index c952df82b515dcd19dadbfee95970368bbf5de1b..cecb230833bed7912ed4ca44e49eec6c00b708a3 100644 (file)
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -6859,6 +6859,60 @@ err_page0:
        return NULL;
 }
 
+static __init struct sk_buff *build_test_skb_linear_no_head_frag(void)
+{
+       unsigned int alloc_size = 2000;
+       unsigned int headroom = 102, doffset = 72, data_size = 1308;
+       struct sk_buff *skb[2];
+       int i;
+
+       /* skbs linked in a frag_list, both with linear data, with head_frag=0
+        * (data allocated by kmalloc), both have tcp data of 1308 bytes
+        * (total payload is 2616 bytes).
+        * Data offset is 72 bytes (40 ipv6 hdr, 32 tcp hdr). Some headroom.
+        */
+       for (i = 0; i < 2; i++) {
+               skb[i] = alloc_skb(alloc_size, GFP_KERNEL);
+               if (!skb[i]) {
+                       if (i == 0)
+                               goto err_skb0;
+                       else
+                               goto err_skb1;
+               }
+
+               skb[i]->protocol = htons(ETH_P_IPV6);
+               skb_reserve(skb[i], headroom);
+               skb_put(skb[i], doffset + data_size);
+               skb_reset_network_header(skb[i]);
+               if (i == 0)
+                       skb_reset_mac_header(skb[i]);
+               else
+                       skb_set_mac_header(skb[i], -ETH_HLEN);
+               __skb_pull(skb[i], doffset);
+       }
+
+       /* setup shinfo.
+        * mimic bpf_skb_proto_4_to_6, which resets gso_segs and assigns a
+        * reduced gso_size.
+        */
+       skb_shinfo(skb[0])->gso_size = 1288;
+       skb_shinfo(skb[0])->gso_type = SKB_GSO_TCPV6 | SKB_GSO_DODGY;
+       skb_shinfo(skb[0])->gso_segs = 0;
+       skb_shinfo(skb[0])->frag_list = skb[1];
+
+       /* adjust skb[0]'s len */
+       skb[0]->len += skb[1]->len;
+       skb[0]->data_len += skb[1]->len;
+       skb[0]->truesize += skb[1]->truesize;
+
+       return skb[0];
+
+err_skb1:
+       kfree_skb(skb[0]);
+err_skb0:
+       return NULL;
+}
+
 struct skb_segment_test {
        const char *descr;
        struct sk_buff *(*build_skb)(void);
@@ -6871,6 +6925,15 @@ static struct skb_segment_test skb_segment_tests[] __initconst = {
                .build_skb = build_test_skb,
                .features = NETIF_F_SG | NETIF_F_GSO_PARTIAL | NETIF_F_IP_CSUM |
                            NETIF_F_IPV6_CSUM | NETIF_F_RXCSUM
+       },
+       {
+               .descr = "gso_linear_no_head_frag",
+               .build_skb = build_test_skb_linear_no_head_frag,
+               .features = NETIF_F_SG | NETIF_F_FRAGLIST |
+                           NETIF_F_HW_VLAN_CTAG_TX | NETIF_F_GSO |
+                           NETIF_F_LLTX_BIT | NETIF_F_GRO |
+                           NETIF_F_IPV6_CSUM | NETIF_F_RXCSUM |
+                           NETIF_F_HW_VLAN_STAG_TX_BIT
        }
 };