netlink: make validation more configurable for future strictness

We currently have two levels of strict validation:

 1) liberal (default)
     - undefined (type >= max) & NLA_UNSPEC attributes accepted
     - attribute length >= expected accepted
     - garbage at end of message accepted
 2) strict (opt-in)
     - NLA_UNSPEC attributes accepted
     - attribute length >= expected accepted

Split out parsing strictness into four different options:
 * TRAILING     - check that there's no trailing data after parsing
                  attributes (in message or nested)
 * MAXTYPE      - reject attrs > max known type
 * UNSPEC       - reject attributes with NLA_UNSPEC policy entries
 * STRICT_ATTRS - strictly validate attribute size

The default for future things should be *everything*.
The current *_strict() is a combination of TRAILING and MAXTYPE,
and is renamed to _deprecated_strict().
The current regular parsing has none of this, and is renamed to
*_parse_deprecated().

Additionally it allows us to selectively set one of the new flags
even on old policies. Notably, the UNSPEC flag could be useful in
this case, since it can be arranged (by filling in the policy) to
not be an incompatible userspace ABI change, but would then going
forward prevent forgetting attribute entries. Similar can apply
to the POLICY flag.

We end up with the following renames:
 * nla_parse           -> nla_parse_deprecated
 * nla_parse_strict    -> nla_parse_deprecated_strict
 * nlmsg_parse         -> nlmsg_parse_deprecated
 * nlmsg_parse_strict  -> nlmsg_parse_deprecated_strict
 * nla_parse_nested    -> nla_parse_nested_deprecated
 * nla_validate_nested -> nla_validate_nested_deprecated

Using spatch, of course:
    @@
    expression TB, MAX, HEAD, LEN, POL, EXT;
    @@
    -nla_parse(TB, MAX, HEAD, LEN, POL, EXT)
    +nla_parse_deprecated(TB, MAX, HEAD, LEN, POL, EXT)

    @@
    expression NLH, HDRLEN, TB, MAX, POL, EXT;
    @@
    -nlmsg_parse(NLH, HDRLEN, TB, MAX, POL, EXT)
    +nlmsg_parse_deprecated(NLH, HDRLEN, TB, MAX, POL, EXT)

    @@
    expression NLH, HDRLEN, TB, MAX, POL, EXT;
    @@
    -nlmsg_parse_strict(NLH, HDRLEN, TB, MAX, POL, EXT)
    +nlmsg_parse_deprecated_strict(NLH, HDRLEN, TB, MAX, POL, EXT)

    @@
    expression TB, MAX, NLA, POL, EXT;
    @@
    -nla_parse_nested(TB, MAX, NLA, POL, EXT)
    +nla_parse_nested_deprecated(TB, MAX, NLA, POL, EXT)

    @@
    expression START, MAX, POL, EXT;
    @@
    -nla_validate_nested(START, MAX, POL, EXT)
    +nla_validate_nested_deprecated(START, MAX, POL, EXT)

    @@
    expression NLH, HDRLEN, MAX, POL, EXT;
    @@
    -nlmsg_validate(NLH, HDRLEN, MAX, POL, EXT)
    +nlmsg_validate_deprecated(NLH, HDRLEN, MAX, POL, EXT)

For this patch, don't actually add the strict, non-renamed versions
yet so that it breaks compile if I get it wrong.

Also, while at it, make nla_validate and nla_parse go down to a
common __nla_validate_parse() function to avoid code duplication.

Ultimately, this allows us to have very strict validation for every
new caller of nla_parse()/nlmsg_parse() etc as re-introduced in the
next patch, while existing things will continue to work as is.

In effect then, this adds fully strict validation for any new command.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 88 insertions, 83 deletions

diff --git a/lib/nlattr.c b/lib/nlattr.c
index 465c9e8ef8a5..af0f8b0309c6 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -69,7 +69,8 @@ static int validate_nla_bitfield32(const struct nlattr *nla,
 
 static int nla_validate_array(const struct nlattr *head, int len, int maxtype,
 			      const struct nla_policy *policy,
-			      struct netlink_ext_ack *extack)
+			      struct netlink_ext_ack *extack,
+			      unsigned int validate)
 {
 	const struct nlattr *entry;
 	int rem;
@@ -86,8 +87,8 @@ static int nla_validate_array(const struct nlattr *head, int len, int maxtype,
 			return -ERANGE;
 		}
 
-		ret = nla_validate(nla_data(entry), nla_len(entry),
-				   maxtype, policy, extack);
+		ret = __nla_validate(nla_data(entry), nla_len(entry),
+				     maxtype, policy, validate, extack);
 		if (ret < 0)
 			return ret;
 	}
@@ -154,7 +155,7 @@ static int nla_validate_int_range(const struct nla_policy *pt,
 }
 
 static int validate_nla(const struct nlattr *nla, int maxtype,
-			const struct nla_policy *policy,
+			const struct nla_policy *policy, unsigned int validate,
 			struct netlink_ext_ack *extack)
 {
 	const struct nla_policy *pt;
@@ -172,6 +173,11 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 	    (pt->type == NLA_EXACT_LEN_WARN && attrlen != pt->len)) {
 		pr_warn_ratelimited("netlink: '%s': attribute type %d has an invalid length.\n",
 				    current->comm, type);
+		if (validate & NL_VALIDATE_STRICT_ATTRS) {
+			NL_SET_ERR_MSG_ATTR(extack, nla,
+					    "invalid attribute length");
+			return -EINVAL;
+		}
 	}
 
 	switch (pt->type) {
@@ -244,8 +250,9 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 		if (attrlen < NLA_HDRLEN)
 			goto out_err;
 		if (pt->validation_data) {
-			err = nla_validate(nla_data(nla), nla_len(nla), pt->len,
-					   pt->validation_data, extack);
+			err = __nla_validate(nla_data(nla), nla_len(nla), pt->len,
+					     pt->validation_data, validate,
+					     extack);
 			if (err < 0) {
 				/*
 				 * return directly to preserve the inner
@@ -268,7 +275,7 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 
 			err = nla_validate_array(nla_data(nla), nla_len(nla),
 						 pt->len, pt->validation_data,
-						 extack);
+						 extack, validate);
 			if (err < 0) {
 				/*
 				 * return directly to preserve the inner
@@ -280,6 +287,12 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 		break;
 
 	case NLA_UNSPEC:
+		if (validate & NL_VALIDATE_UNSPEC) {
+			NL_SET_ERR_MSG_ATTR(extack, nla,
+					    "Unsupported attribute");
+			return -EINVAL;
+		}
+		/* fall through */
 	case NLA_MIN_LEN:
 		if (attrlen < pt->len)
 			goto out_err;
@@ -322,37 +335,75 @@ out_err:
 	return err;
 }
 
+static int __nla_validate_parse(const struct nlattr *head, int len, int maxtype,
+				const struct nla_policy *policy,
+				unsigned int validate,
+				struct netlink_ext_ack *extack,
+				struct nlattr **tb)
+{
+	const struct nlattr *nla;
+	int rem;
+
+	if (tb)
+		memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
+
+	nla_for_each_attr(nla, head, len, rem) {
+		u16 type = nla_type(nla);
+
+		if (type == 0 || type > maxtype) {
+			if (validate & NL_VALIDATE_MAXTYPE) {
+				NL_SET_ERR_MSG(extack, "Unknown attribute type");
+				return -EINVAL;
+			}
+			continue;
+		}
+		if (policy) {
+			int err = validate_nla(nla, maxtype, policy,
+					       validate, extack);
+
+			if (err < 0)
+				return err;
+		}
+
+		if (tb)
+			tb[type] = (struct nlattr *)nla;
+	}
+
+	if (unlikely(rem > 0)) {
+		pr_warn_ratelimited("netlink: %d bytes leftover after parsing attributes in process `%s'.\n",
+				    rem, current->comm);
+		NL_SET_ERR_MSG(extack, "bytes leftover after parsing attributes");
+		if (validate & NL_VALIDATE_TRAILING)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
 /**
- * nla_validate - Validate a stream of attributes
+ * __nla_validate - Validate a stream of attributes
  * @head: head of attribute stream
  * @len: length of attribute stream
  * @maxtype: maximum attribute type to be expected
  * @policy: validation policy
+ * @validate: validation strictness
  * @extack: extended ACK report struct
  *
  * Validates all attributes in the specified attribute stream against the
- * specified policy. Attributes with a type exceeding maxtype will be
- * ignored. See documenation of struct nla_policy for more details.
+ * specified policy. Validation depends on the validate flags passed, see
+ * &enum netlink_validation for more details on that.
+ * See documenation of struct nla_policy for more details.
  *
  * Returns 0 on success or a negative error code.
  */
-int nla_validate(const struct nlattr *head, int len, int maxtype,
-		 const struct nla_policy *policy,
-		 struct netlink_ext_ack *extack)
+int __nla_validate(const struct nlattr *head, int len, int maxtype,
+		   const struct nla_policy *policy, unsigned int validate,
+		   struct netlink_ext_ack *extack)
 {
-	const struct nlattr *nla;
-	int rem;
-
-	nla_for_each_attr(nla, head, len, rem) {
-		int err = validate_nla(nla, maxtype, policy, extack);
-
-		if (err < 0)
-			return err;
-	}
-
-	return 0;
+	return __nla_validate_parse(head, len, maxtype, policy, validate,
+				    extack, NULL);
 }
-EXPORT_SYMBOL(nla_validate);
+EXPORT_SYMBOL(__nla_validate);
 
 /**
  * nla_policy_len - Determin the max. length of a policy
@@ -384,76 +435,30 @@ nla_policy_len(const struct nla_policy *p, int n)
 EXPORT_SYMBOL(nla_policy_len);
 
 /**
- * nla_parse - Parse a stream of attributes into a tb buffer
+ * __nla_parse - Parse a stream of attributes into a tb buffer
  * @tb: destination array with maxtype+1 elements
  * @maxtype: maximum attribute type to be expected
  * @head: head of attribute stream
  * @len: length of attribute stream
  * @policy: validation policy
+ * @validate: validation strictness
+ * @extack: extended ACK pointer
  *
  * Parses a stream of attributes and stores a pointer to each attribute in
- * the tb array accessible via the attribute type. Attributes with a type
- * exceeding maxtype will be silently ignored for backwards compatibility
- * reasons. policy may be set to NULL if no validation is required.
+ * the tb array accessible via the attribute type.
+ * Validation is controlled by the @validate parameter.
  *
  * Returns 0 on success or a negative error code.
  */
-static int __nla_parse(struct nlattr **tb, int maxtype,
-		       const struct nlattr *head, int len,
-		       bool strict, const struct nla_policy *policy,
-		       struct netlink_ext_ack *extack)
-{
-	const struct nlattr *nla;
-	int rem;
-
-	memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
-
-	nla_for_each_attr(nla, head, len, rem) {
-		u16 type = nla_type(nla);
-
-		if (type == 0 || type > maxtype) {
-			if (strict) {
-				NL_SET_ERR_MSG(extack, "Unknown attribute type");
-				return -EINVAL;
-			}
-			continue;
-		}
-		if (policy) {
-			int err = validate_nla(nla, maxtype, policy, extack);
-
-			if (err < 0)
-				return err;
-		}
-
-		tb[type] = (struct nlattr *)nla;
-	}
-
-	if (unlikely(rem > 0)) {
-		pr_warn_ratelimited("netlink: %d bytes leftover after parsing attributes in process `%s'.\n",
-				    rem, current->comm);
-		NL_SET_ERR_MSG(extack, "bytes leftover after parsing attributes");
-		if (strict)
-			return -EINVAL;
-	}
-
-	return 0;
-}
-
-int nla_parse(struct nlattr **tb, int maxtype, const struct nlattr *head,
-	      int len, const struct nla_policy *policy,
-	      struct netlink_ext_ack *extack)
-{
-	return __nla_parse(tb, maxtype, head, len, false, policy, extack);
-}
-EXPORT_SYMBOL(nla_parse);
-
-int nla_parse_strict(struct nlattr **tb, int maxtype, const struct nlattr *head,
-		     int len, const struct nla_policy *policy,
-		     struct netlink_ext_ack *extack)
+int __nla_parse(struct nlattr **tb, int maxtype,
+		const struct nlattr *head, int len,
+		const struct nla_policy *policy, unsigned int validate,
+		struct netlink_ext_ack *extack)
 {
-	return __nla_parse(tb, maxtype, head, len, true, policy, extack);
+	return __nla_validate_parse(head, len, maxtype, policy, validate,
+				    extack, tb);
 }
-EXPORT_SYMBOL(nla_parse_strict);
+EXPORT_SYMBOL(__nla_parse);
 
 /**
  * nla_find - Find a specific attribute in a stream of attributes