[PATCH 3.10 015/180] netfilter: x_tables: don't reject valid target size on some architectures

[Willy Tarreau]

From: Florian Westphal <fw@xxxxxxxxx>

commit 7b7eba0f3515fca3296b8881d583f7c1042f5226 upstream.

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@xxxxxxxxxx>
Tested-by: John Stultz <john.stultz@xxxxxxxxxx>
Fixes: 7ed2abddd20cf ("netfilter: x_tables: check standard target size too")
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
---
 net/netfilter/x_tables.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index c482633..6ac9fb4 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -628,7 +628,7 @@ 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,
@@ -710,7 +710,7 @@ 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,
-- 
2.8.0.rc2.1.gbe9624a