Commit 7b7eba0f authored Jun 01, 2016 by Florian Westphal Committed by Pablo Neira Ayuso Jun 02, 2016

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



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: 7ed2abdd ("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>

parent 14b84e86

net/netfilter/x_tables.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -612,7 +612,7 @@ 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,
		@@ -694,7 +694,7 @@ 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,

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