Subject: [PATCH net v2] gso: validate gso_type if SKB_GSO_DODGY

From: Willem de Bruijn <[email-masked]>
Date: Thu, 18 Jan 2018 19:19:59 -0500

From: Willem de Bruijn <[email-masked]>

Validate gso_type during segmentation as SKB_GSO_DODGY sources
may pass packets where the gso_type does not match the contents.

Syzkaller was able to enter the SCTP gso handler with a packet of
gso_type SKB_GSO_TCPV4.

On entry of transport layer gso handlers, verify that the gso_type
matches the transport protocol.

Fixes: f43798c27684 ("tun: Allow GSO using virtio_net_hdr")
Link: http://lkml.kernel.org/r/<[email-masked]>
Reported-by: [email-masked]
Signed-off-by: Willem de Bruijn <[email-masked]>

---
Similar checks existed until removed in commit 5c7cdf339af5 ("gso:
Remove arbitrary checks for unsupported GSO"). But those were limited
to the TSO path, not software GSO. I believe that this issue goes
back further, hence the Fixes at the first user of virtio_net_hdr.
---
 net/ipv4/esp4_offload.c  | 3 +++
 net/ipv4/tcp_offload.c   | 3 +++
 net/ipv4/udp_offload.c   | 3 +++
 net/ipv6/esp6_offload.c  | 3 +++
 net/ipv6/tcpv6_offload.c | 3 +++
 net/ipv6/udp_offload.c   | 3 +++
 net/sctp/offload.c       | 3 +++
 7 files changed, 21 insertions(+)

diff --git a/net/ipv4/esp4_offload.c b/net/ipv4/esp4_offload.c
index b1338e576d00..29b333a62ab0 100644
--- a/net/ipv4/esp4_offload.c
+++ b/net/ipv4/esp4_offload.c
@@ -122,6 +122,9 @@ static struct sk_buff *esp4_gso_segment(struct sk_buff *skb,
 	if (!xo)
 		goto out;
 
+	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_ESP))
+		goto out;
+
 	seq = xo->seq.low;
 
 	x = skb->sp->xvec[skb->sp->len - 1];
diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
index b6a2aa1dcf56..4d58e2ce0b5b 100644
--- a/net/ipv4/tcp_offload.c
+++ b/net/ipv4/tcp_offload.c
@@ -32,6 +32,9 @@ static void tcp_gso_tstamp(struct sk_buff *skb, unsigned int ts_seq,
 static struct sk_buff *tcp4_gso_segment(struct sk_buff *skb,
 					netdev_features_t features)
 {
+	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4))
+		return ERR_PTR(-EINVAL);
+
 	if (!pskb_may_pull(skb, sizeof(struct tcphdr)))
 		return ERR_PTR(-EINVAL);
 
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 01801b77bd0d..ea6e6e7df0ee 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -203,6 +203,9 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 		goto out;
 	}
 
+	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP))
+		goto out;
+
 	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
 		goto out;
 
diff --git a/net/ipv6/esp6_offload.c b/net/ipv6/esp6_offload.c
index dd9627490c7c..f52c314d4c97 100644
--- a/net/ipv6/esp6_offload.c
+++ b/net/ipv6/esp6_offload.c
@@ -149,6 +149,9 @@ static struct sk_buff *esp6_gso_segment(struct sk_buff *skb,
 	if (!xo)
 		goto out;
 
+	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_ESP))
+		goto out;
+
 	seq = xo->seq.low;
 
 	x = skb->sp->xvec[skb->sp->len - 1];
diff --git a/net/ipv6/tcpv6_offload.c b/net/ipv6/tcpv6_offload.c
index d883c9204c01..278e49cd67d4 100644
--- a/net/ipv6/tcpv6_offload.c
+++ b/net/ipv6/tcpv6_offload.c
@@ -46,6 +46,9 @@ static struct sk_buff *tcp6_gso_segment(struct sk_buff *skb,
 {
 	struct tcphdr *th;
 
+	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6))
+		return ERR_PTR(-EINVAL);
+
 	if (!pskb_may_pull(skb, sizeof(*th)))
 		return ERR_PTR(-EINVAL);
 
diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
index a0f89ad76f9d..2a04dc9c781b 100644
--- a/net/ipv6/udp_offload.c
+++ b/net/ipv6/udp_offload.c
@@ -42,6 +42,9 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
 		const struct ipv6hdr *ipv6h;
 		struct udphdr *uh;
 
+		if (!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP))
+			goto out;
+
 		if (!pskb_may_pull(skb, sizeof(struct udphdr)))
 			goto out;
 
diff --git a/net/sctp/offload.c b/net/sctp/offload.c
index 275925b93b29..35bc7106d182 100644
--- a/net/sctp/offload.c
+++ b/net/sctp/offload.c
@@ -45,6 +45,9 @@ static struct sk_buff *sctp_gso_segment(struct sk_buff *skb,
 	struct sk_buff *segs = ERR_PTR(-EINVAL);
 	struct sctphdr *sh;
 
+	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_SCTP))
+		goto out;
+
 	sh = sctp_hdr(skb);
 	if (!pskb_may_pull(skb, sizeof(*sh)))
 		goto out;
-- 
2.16.0.rc1.238.g530d649a79-goog