netfilter: x_tables: don't reject valid target size on some architectures

Orabug: 24690280
CVE: CVE-2016-3134

[ Upstream commit 7b7eba0f3515fca3296b8881d583f7c1042f5226 ]

Quoting John Stultz:
  In updating a 32bit arm device from 4.6 to Linus' current HEAD, I
  noticed I was having some trouble with networking, and realized that
  /proc/net/ip_tables_names was suddenly empty.
  Digging through the registration process, it seems we're catching on the:

   if (strcmp(t->u.user.name, XT_STANDARD_TARGET) == 0 &&
       target_offset + sizeof(struct xt_standard_target) != next_offset)
         return -EINVAL;

  Where next_offset seems to be 4 bytes larger then the
  offset + standard_target struct size.

next_offset needs to be aligned via XT_ALIGN (so we can access all members
of ip(6)t_entry struct).

This problem didn't show up on i686 as it only needs 4-byte alignment for
u64, but iptables userspace on other 32bit arches does insert extra padding.

Reported-by: John Stultz <john.stultz@linaro.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Fixes: 7ed2abddd20cf ("netfilter: x_tables: check standard target size too")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
(cherry picked from commit d97246b5d16b77b57d835b6b4d1bde8ea6566b46)
Signed-off-by: Brian Maly <brian.maly@oracle.com>

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 239d71bba8defcc90a92cec928db28ac1722e9f5..7ad7e6038af0298e57cf96b3659bab4941cd679f 100644 (file)
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -611,7 +611,7 @@ int xt_compat_check_entry_offsets(const void *base, const char *elems,
                return -EINVAL;
 
        if (strcmp(t->u.user.name, XT_STANDARD_TARGET) == 0 &&
-           target_offset + sizeof(struct compat_xt_standard_target) != next_offset)
+           COMPAT_XT_ALIGN(target_offset + sizeof(struct compat_xt_standard_target)) != next_offset)
                return -EINVAL;
 
        /* compat_xt_entry match has less strict aligment requirements,
@@ -693,7 +693,7 @@ int xt_check_entry_offsets(const void *base,
                return -EINVAL;
 
        if (strcmp(t->u.user.name, XT_STANDARD_TARGET) == 0 &&
-           target_offset + sizeof(struct xt_standard_target) != next_offset)
+           XT_ALIGN(target_offset + sizeof(struct xt_standard_target)) != next_offset)
                return -EINVAL;
 
        return xt_check_entry_match(elems, base + target_offset,