[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>

1 files changed, 11 insertions, 4 deletions

diff --git a/include/net/netlink.h b/include/net/netlink.h
index bcb27e3a312..11dc2e7f679 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;
 };
 
 /**