linux-kernel - [PATCH 3.16 294/305] netfilter: x_tables: check standard target size too

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Message-ID: <lsq.1471110171.991221348@decadent.org.uk>
Date:	Sat, 13 Aug 2016 18:42:51 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Florian Westphal" <fw@...len.de>,
	"Pablo Neira Ayuso" <pablo@...filter.org>
Subject: [PATCH 3.16 294/305] netfilter: x_tables: check standard target
 size too

3.16.37-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Florian Westphal <fw@...len.de>

commit 7ed2abddd20cf8f6bd27f65bd218f26fa5bf7f44 upstream.

We have targets and standard targets -- the latter carries a verdict.

The ip/ip6tables validation functions will access t->verdict for the
standard targets to fetch the jump offset or verdict for chainloop
detection, but this happens before the targets get checked/validated.

Thus we also need to check for verdict presence here, else t->verdict
can point right after a blob.

Spotted with UBSAN while testing malformed blobs.

Signed-off-by: Florian Westphal <fw@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/netfilter/x_tables.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -559,6 +559,13 @@ int xt_compat_match_to_user(const struct
 }
 EXPORT_SYMBOL_GPL(xt_compat_match_to_user);
 
+/* non-compat version may have padding after verdict */
+struct compat_xt_standard_target {
+	struct compat_xt_entry_target t;
+	compat_uint_t verdict;
+};
+
+/* see xt_check_entry_offsets */
 int xt_compat_check_entry_offsets(const void *base,
 				  unsigned int target_offset,
 				  unsigned int next_offset)
@@ -576,6 +583,10 @@ int xt_compat_check_entry_offsets(const
 	if (target_offset + t->u.target_size > next_offset)
 		return -EINVAL;
 
+	if (strcmp(t->u.user.name, XT_STANDARD_TARGET) == 0 &&
+	    target_offset + sizeof(struct compat_xt_standard_target) != next_offset)
+		return -EINVAL;
+
 	return 0;
 }
 EXPORT_SYMBOL(xt_compat_check_entry_offsets);
@@ -615,6 +626,10 @@ int xt_check_entry_offsets(const void *b
 	if (target_offset + t->u.target_size > next_offset)
 		return -EINVAL;
 
+	if (strcmp(t->u.user.name, XT_STANDARD_TARGET) == 0 &&
+	    target_offset + sizeof(struct xt_standard_target) != next_offset)
+		return -EINVAL;
+
 	return 0;
 }
 EXPORT_SYMBOL(xt_check_entry_offsets);