[NETLINK]: Improve string attribute validation

Introduces a new attribute type NLA_NUL_STRING to support NUL
terminated strings. Attributes of this kind require to carry
a terminating NUL within the maximum specified in the policy.

The `old' NLA_STRING which is not required to be NUL terminated
is extended to provide means to specify a maximum length of the
string.

Aims at easing the pain with using nla_strlcpy() on temporary
buffers.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 50 insertions, 14 deletions

diff --git a/include/net/netlink.h b/include/net/netlink.h
index bcb27e3a312e..11dc2e7f679a 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -167,6 +167,7 @@ enum {
         NLA_FLAG,
         NLA_MSECS,
         NLA_NESTED,
+        NLA_NUL_STRING,
         __NLA_TYPE_MAX,
 };
 
@@ -175,21 +176,27 @@ enum {
 /**
  * struct nla_policy - attribute validation policy
  * @type: Type of attribute or NLA_UNSPEC
- * @minlen: Minimal length of payload required to be available
+ * @len: Type specific length of payload
  *
  * Policies are defined as arrays of this struct, the array must be
  * accessible by attribute type up to the highest identifier to be expected.
  *
+ * Meaning of `len' field:
+ *    NLA_STRING           Maximum length of string
+ *    NLA_NUL_STRING       Maximum length of string (excluding NUL)
+ *    NLA_FLAG             Unused
+ *    All other            Exact length of attribute payload
+ *
  * Example:
  * static struct nla_policy my_policy[ATTR_MAX+1] __read_mostly = {
  *      [ATTR_FOO] = { .type = NLA_U16 },
- *      [ATTR_BAR] = { .type = NLA_STRING },
- *      [ATTR_BAZ] = { .minlen = sizeof(struct mystruct) },
+ *      [ATTR_BAR] = { .type = NLA_STRING, len = BARSIZ },
+ *      [ATTR_BAZ] = { .len = sizeof(struct mystruct) },
  * };
  */
 struct nla_policy {
         u16             type;
-        u16             minlen;
+        u16             len;
 };
 
 /**
diff --git a/net/netlink/attr.c b/net/netlink/attr.c
index 136e529e5780..004139557e09 100644
--- a/net/netlink/attr.c
+++ b/net/netlink/attr.c
@@ -20,7 +20,6 @@ static u16 nla_attr_minlen[NLA_TYPE_MAX+1] __read_mostly = {
         [NLA_U16]       = sizeof(u16),
         [NLA_U32]       = sizeof(u32),
         [NLA_U64]       = sizeof(u64),
-        [NLA_STRING]    = 1,
         [NLA_NESTED]    = NLA_HDRLEN,
 };
 
@@ -28,7 +27,7 @@ static int validate_nla(struct nlattr *nla, int maxtype,
                         struct nla_policy *policy)
 {
         struct nla_policy *pt;
-        int minlen = 0;
+        int minlen = 0, attrlen = nla_len(nla);
 
         if (nla->nla_type <= 0 || nla->nla_type > maxtype)
                 return 0;
@@ -37,16 +36,46 @@ static int validate_nla(struct nlattr *nla, int maxtype,
 
         BUG_ON(pt->type > NLA_TYPE_MAX);
 
-        if (pt->minlen)
-                minlen = pt->minlen;
-        else if (pt->type != NLA_UNSPEC)
-                minlen = nla_attr_minlen[pt->type];
+        switch (pt->type) {
+        case NLA_FLAG:
+                if (attrlen > 0)
+                        return -ERANGE;
+                break;
 
-        if (pt->type == NLA_FLAG && nla_len(nla) > 0)
-                return -ERANGE;
+        case NLA_NUL_STRING:
+                if (pt->len)
+                        minlen = min_t(int, attrlen, pt->len + 1);
+                else
+                        minlen = attrlen;
 
-        if (nla_len(nla) < minlen)
-                return -ERANGE;
+                if (!minlen || memchr(nla_data(nla), '\0', minlen) == NULL)
+                        return -EINVAL;
+                /* fall through */
+
+        case NLA_STRING:
+                if (attrlen < 1)
+                        return -ERANGE;
+
+                if (pt->len) {
+                        char *buf = nla_data(nla);
+
+                        if (buf[attrlen - 1] == '\0')
+                                attrlen--;
+
+                        if (attrlen > pt->len)
+                                return -ERANGE;
+                }
+                break;
+
+        default:
+                if (pt->len)
+                        minlen = pt->len;
+                else if (pt->type != NLA_UNSPEC)
+                        minlen = nla_attr_minlen[pt->type];
+
+                if (attrlen < minlen)
+                        return -ERANGE;
+        }
 
         return 0;
 }