Subject: [PATCH v2 net-next] net: netlink: Update attr validation to require exact length for some types

From: David Ahern <[email-masked]>
Date: Tue, 7 Nov 2017 21:59:40 -0800

Attributes using NLA_U* and NLA_S* (where * is 8, 16,32 and 64) are
expected to be an exact length. Split these data types from
nla_attr_minlen into nla_attr_len and update validate_nla to require
the attribute to have exact length for them.

Signed-off-by: David Ahern <[email-masked]>
---
v2
- fix check in nla_policy_len - reported by kernel test robot

 lib/nlattr.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/lib/nlattr.c b/lib/nlattr.c
index 3d8295c85505..8bf78b4b78f0 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -15,19 +15,23 @@
 #include <linux/types.h>
 #include <net/netlink.h>
 
-static const u8 nla_attr_minlen[NLA_TYPE_MAX+1] = {
+/* for these data types attribute length must be exactly given size */
+static const u8 nla_attr_len[NLA_TYPE_MAX+1] = {
 	[NLA_U8]	= sizeof(u8),
 	[NLA_U16]	= sizeof(u16),
 	[NLA_U32]	= sizeof(u32),
 	[NLA_U64]	= sizeof(u64),
-	[NLA_MSECS]	= sizeof(u64),
-	[NLA_NESTED]	= NLA_HDRLEN,
 	[NLA_S8]	= sizeof(s8),
 	[NLA_S16]	= sizeof(s16),
 	[NLA_S32]	= sizeof(s32),
 	[NLA_S64]	= sizeof(s64),
 };
 
+static const u8 nla_attr_minlen[NLA_TYPE_MAX+1] = {
+	[NLA_MSECS]	= sizeof(u64),
+	[NLA_NESTED]	= NLA_HDRLEN,
+};
+
 static int validate_nla_bitfield32(const struct nlattr *nla,
 				   u32 *valid_flags_allowed)
 {
@@ -65,6 +69,13 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 
 	BUG_ON(pt->type > NLA_TYPE_MAX);
 
+	/* for data types NLA_U* and NLA_S* require exact length */
+	if (nla_attr_len[pt->type]) {
+		if (attrlen != nla_attr_len[pt->type])
+			return -ERANGE;
+		return 0;
+	}
+
 	switch (pt->type) {
 	case NLA_FLAG:
 		if (attrlen > 0)
@@ -191,6 +202,8 @@ nla_policy_len(const struct nla_policy *p, int n)
 	for (i = 0; i < n; i++, p++) {
 		if (p->len)
 			len += nla_total_size(p->len);
+		else if (nla_attr_len[p->type])
+			len += nla_total_size(nla_attr_len[p->type]);
 		else if (nla_attr_minlen[p->type])
 			len += nla_total_size(nla_attr_minlen[p->type]);
 	}
-- 
2.1.4