[PATCH 5.10 296/406] dccp: Fix out of bounds access in DCCP error handler

Greg Kroah-Hartman
2023-09-17T19:37:00Z

From: Jann Horn <jannh@google.com>

commit 977ad86c2a1bcaf58f01ab98df5cc145083c489c upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/dccp/ipv4.c | 13 +++++++++----
net/dccp/ipv6.c | 15 ++++++++++-----
2 files changed, 19 insertions(+), 9 deletions(-)

--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -243,12 +243,17 @@ static int dccp_v4_err(struct sk_buff *s
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,
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -67,7 +67,7 @@ static inline __u64 dccp_v6_init_sequenc
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;
@@ -76,12 +76,17 @@ static int dccp_v6_err(struct sk_buff *s
__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,