netfilter: ip6t_NPT: Fix translation for non-multiple of 32 prefix lengths

The bitmask used for the prefix mangling was being calculated
incorrectly, leading to the wrong part of the address being replaced
when the prefix length wasn't a multiple of 32.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/ipv6/netfilter/ip6t_NPT.c b/net/ipv6/netfilter/ip6t_NPT.c
index 33608c610276d87e9845b75555fadc6771765606..cb631143721c0afb13152121c74a9d49f51e99dc 100644 (file)
--- a/net/ipv6/netfilter/ip6t_NPT.c
+++ b/net/ipv6/netfilter/ip6t_NPT.c
@@ -57,7 +57,7 @@ static bool ip6t_npt_map_pfx(const struct ip6t_npt_tginfo *npt,
                if (pfx_len - i >= 32)
                        mask = 0;
                else
-                       mask = htonl(~((1 << (pfx_len - i)) - 1));
+                       mask = htonl((1 << (i - pfx_len + 32)) - 1);
 
                idx = i / 32;
                addr->s6_addr32[idx] &= mask;