3.16.54-rc1 review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
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@google.com Reported-by: Denys Fedoryshchenko nuclearcat@nuclearcat.com Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org Signed-off-by: Ben Hutchings ben@decadent.org.uk --- net/netfilter/xt_TCPMSS.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
--- 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.. */