dccp: Fix out of bounds access in DCCP error handler

There was a previous attempt to fix an out-of-bounds access in the DCCP
error handlers, but that fix assumed that the error handlers only want
to access the first 8 bytes of the DCCP header. Actually, they also look
at the DCCP sequence number, which is stored beyond 8 bytes, so an
explicit pskb_may_pull() is required.

Fixes: 6706a97fec96 ("dccp: fix out of bound access in dccp_v4_err()")
Fixes: 1aa9d1a0e7ee ("ipv6: dccp: fix out of bound access in dccp_v6_err()")
Cc: stable@vger.kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index a545ad7..a5361fb 100644 (file)
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -255,12 +255,17 @@ static int dccp_v4_err(struct sk_buff *skb, u32 info)
        int err;
        struct net *net = dev_net(skb->dev);
 
-       /* Only need dccph_dport & dccph_sport which are the first
-        * 4 bytes in dccp header.
+       /* For the first __dccp_basic_hdr_len() check, we only need dh->dccph_x,
+        * which is in byte 7 of the dccp header.
         * Our caller (icmp_socket_deliver()) already pulled 8 bytes for us.
+        *
+        * Later on, we want to access the sequence number fields, which are
+        * beyond 8 bytes, so we have to pskb_may_pull() ourselves.
         */
-       BUILD_BUG_ON(offsetofend(struct dccp_hdr, dccph_sport) > 8);
-       BUILD_BUG_ON(offsetofend(struct dccp_hdr, dccph_dport) > 8);
+       dh = (struct dccp_hdr *)(skb->data + offset);
+       if (!pskb_may_pull(skb, offset + __dccp_basic_hdr_len(dh)))
+               return -EINVAL;
+       iph = (struct iphdr *)skb->data;
        dh = (struct dccp_hdr *)(skb->data + offset);
 
        sk = __inet_lookup_established(net, &dccp_hashinfo,

diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index d29d116..25816e7 100644 (file)
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -74,7 +74,7 @@ static inline __u64 dccp_v6_init_sequence(struct sk_buff *skb)
 static int dccp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
                        u8 type, u8 code, int offset, __be32 info)
 {
-       const struct ipv6hdr *hdr = (const struct ipv6hdr *)skb->data;
+       const struct ipv6hdr *hdr;
        const struct dccp_hdr *dh;
        struct dccp_sock *dp;
        struct ipv6_pinfo *np;
@@ -83,12 +83,17 @@ static int dccp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
        __u64 seq;
        struct net *net = dev_net(skb->dev);
 
-       /* Only need dccph_dport & dccph_sport which are the first
-        * 4 bytes in dccp header.
+       /* For the first __dccp_basic_hdr_len() check, we only need dh->dccph_x,
+        * which is in byte 7 of the dccp header.
         * Our caller (icmpv6_notify()) already pulled 8 bytes for us.
+        *
+        * Later on, we want to access the sequence number fields, which are
+        * beyond 8 bytes, so we have to pskb_may_pull() ourselves.
         */
-       BUILD_BUG_ON(offsetofend(struct dccp_hdr, dccph_sport) > 8);
-       BUILD_BUG_ON(offsetofend(struct dccp_hdr, dccph_dport) > 8);
+       dh = (struct dccp_hdr *)(skb->data + offset);
+       if (!pskb_may_pull(skb, offset + __dccp_basic_hdr_len(dh)))
+               return -EINVAL;
+       hdr = (const struct ipv6hdr *)skb->data;
        dh = (struct dccp_hdr *)(skb->data + offset);
 
        sk = __inet6_lookup_established(net, &dccp_hashinfo,