netfilter: synproxy: Fix out of bounds when parsing TCP options

The TCP option parser in synproxy (synproxy_parse_options) could read
one byte out of bounds. When the length is 1, the execution flow gets
into the loop, reads one byte of the opcode, and if the opcode is
neither TCPOPT_EOL nor TCPOPT_NOP, it reads one more byte, which exceeds
the length of 1.

This fix is inspired by commit fae93b8ae922 ("ipv4: tcp_input: fix stack
out of bounds when parsing TCP options.").

v2 changes:

Added an early return when length < 0 to avoid calling
skb_header_pointer with negative length.

Cc: Young Xiao <92siuyang@gmail.com>
Fixes: da05c55e4400 ("netfilter: add SYNPROXY core/target")
Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/netfilter/nf_synproxy_core.c b/net/netfilter/nf_synproxy_core.c
index b100c04a0e43593305356297d3d8ff1956f5c407..3d6d49420db8bffa54db87ce9999d036fa3f091c 100644 (file)
--- a/net/netfilter/nf_synproxy_core.c
+++ b/net/netfilter/nf_synproxy_core.c
@@ -31,6 +31,9 @@ synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
        int length = (th->doff * 4) - sizeof(*th);
        u8 buf[40], *ptr;
 
+       if (unlikely(length < 0))
+               return false;
+
        ptr = skb_header_pointer(skb, doff + sizeof(*th), length, buf);
        if (ptr == NULL)
                return false;
@@ -47,6 +50,8 @@ synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
                        length--;
                        continue;
                default:
+                       if (length < 2)
+                               return true;
                        opsize = *ptr++;
                        if (opsize < 2)
                                return true;