From: Eric Dumazet <edumazet@xxxxxxxxxx>
commit 2638fd0f92d4397884fd991d8f4925cb3f081901 upstream.
Denys provided an awesome KASAN report pointing to an use
after free in xt_TCPMSS
I have provided three patches to fix this issue, either in xt_TCPMSS or
in xt_tcpudp.c. It seems xt_TCPMSS patch has the smallest possible
impact.
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reported-by: Denys Fedoryshchenko <nuclearcat@xxxxxxxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
[wt: adjust context]
Signed-off-by: Willy Tarreau <w@xxxxxx>
---
net/netfilter/xt_TCPMSS.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index 7011c71..c656269 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -68,7 +68,7 @@ tcpmss_mangle_packet(struct sk_buff *skb,
tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
/* Header cannot be larger than the packet */
- if (tcplen < tcph->doff*4)
+ if (tcplen < tcph->doff*4 || tcph->doff*4 < sizeof(struct tcphdr))
return -1;
if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
@@ -117,6 +117,10 @@ tcpmss_mangle_packet(struct sk_buff *skb,
if (tcplen > tcph->doff*4)
return 0;
+ /* tcph->doff has 4 bits, do not wrap it to 0 */
+ if (tcph->doff >= 15)
+ return 0;
+
/*
* MSS Option not found ?! add it..
*/
--
2.8.0.rc2.1.gbe9624a