Commit a7776b88 authored by Eric Dumazet's avatar Eric Dumazet Committed by Sasha Levin

netfilter: xt_TCPMSS: add more sanity tests on tcph->doff

[ Upstream commit 2638fd0f ]

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: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarDenys Fedoryshchenko <nuclearcat@nuclearcat.com>
Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: default avatarSasha Levin <alexander.levin@verizon.com>
parent 2b1915e2
...@@ -104,7 +104,7 @@ tcpmss_mangle_packet(struct sk_buff *skb, ...@@ -104,7 +104,7 @@ tcpmss_mangle_packet(struct sk_buff *skb,
tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff); tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
tcp_hdrlen = tcph->doff * 4; tcp_hdrlen = tcph->doff * 4;
if (len < tcp_hdrlen) if (len < tcp_hdrlen || tcp_hdrlen < sizeof(struct tcphdr))
return -1; return -1;
if (info->mss == XT_TCPMSS_CLAMP_PMTU) { if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
...@@ -156,6 +156,10 @@ tcpmss_mangle_packet(struct sk_buff *skb, ...@@ -156,6 +156,10 @@ tcpmss_mangle_packet(struct sk_buff *skb,
if (len > tcp_hdrlen) if (len > tcp_hdrlen)
return 0; return 0;
/* tcph->doff has 4 bits, do not wrap it to 0 */
if (tcp_hdrlen >= 15 * 4)
return 0;
/* /*
* MSS Option not found ?! add it.. * MSS Option not found ?! add it..
*/ */
......
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