[Trusty][Zesty][SRU][PATCH 0/1] Fix for CVE-2017-18017

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[Trusty][Zesty][SRU][PATCH 0/1] Fix for CVE-2017-18017

Po-Hsu Lin (Sam)
From our CVE tracker, only Trusty and Zesty need this patch
and it can be cherry-picked for both of them.

This patch fixes an use after free issue in xt_TCPMSS.

Eric Dumazet (1):
  netfilter: xt_TCPMSS: add more sanity tests on tcph->doff

 net/netfilter/xt_TCPMSS.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--
2.7.4


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[CVE-2017-18017][Trusty][Zesty][PATCH 1/1] netfilter: xt_TCPMSS: add more sanity tests on tcph->doff

Po-Hsu Lin (Sam)
From: Eric Dumazet <[hidden email]>

CVE-2017-18017

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 <[hidden email]>
Reported-by: Denys Fedoryshchenko <[hidden email]>
Signed-off-by: Pablo Neira Ayuso <[hidden email]>
(cherry picked from commit 2638fd0f92d4397884fd991d8f4925cb3f081901)
Signed-off-by: Po-Hsu Lin <[hidden email]>
---
 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 e762de5..6531d70 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -104,7 +104,7 @@ tcpmss_mangle_packet(struct sk_buff *skb,
  tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
  tcp_hdrlen = tcph->doff * 4;
 
- if (len < tcp_hdrlen)
+ if (len < tcp_hdrlen || tcp_hdrlen < sizeof(struct tcphdr))
  return -1;
 
  if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
@@ -156,6 +156,10 @@ tcpmss_mangle_packet(struct sk_buff *skb,
  if (len > tcp_hdrlen)
  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..
  */
--
2.7.4


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