[PATCH 3.12 36/88] netfilter: x_tables: don't reject valid target size on some architectures

From: Jiri Slaby
Date: Thu Jul 14 2016 - 04:41:38 EST

From: Florian Westphal <fw@xxxxxxxxx>

3.12-stable review patch. If anyone has any objections, please let me know.


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: Jiri Slaby <jslaby@xxxxxxx>
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 c4826337866b..6ac9fb4f42fc 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,