apparmor: provide a bounded version of label_parse

some label/context sources might not be guaranteed to be null terminiated
provide a size bounded version of label parse to deal with these.
Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>

security/apparmor/include/label.h

@@ -327,6 +327,9 @@ void aa_label_audit(struct audit_buffer *ab, struct aa_label *label, gfp_t gfp);
 void aa_label_seq_print(struct seq_file *f, struct aa_label *label, gfp_t gfp);
 void aa_label_printk(struct aa_label *label, gfp_t gfp);
 
+struct aa_label *aa_label_strn_parse(struct aa_label *base, const char *str,
+				     size_t n, gfp_t gfp, bool create,
+				     bool force_stack);
 struct aa_label *aa_label_parse(struct aa_label *base, const char *str,
 				gfp_t gfp, bool create, bool force_stack);
 

security/apparmor/label.c

@@ -1808,16 +1808,17 @@ void aa_label_printk(struct aa_label *label, gfp_t gfp)
 	aa_put_ns(ns);
 }
 
-static int label_count_str_entries(const char *str)
+static int label_count_strn_entries(const char *str, size_t n)
 {
+	const char *end = str + n;
 	const char *split;
 	int count = 1;
 
 	AA_BUG(!str);
 
-	for (split = aa_label_str_split(str);
+	for (split = aa_label_strn_split(str, end - str);
 	     split;
-	     split = aa_label_str_split(str)) {
+	     split = aa_label_strn_split(str, end - str)) {
 		count++;
 		str = split + 3;
 	}
@@ -1845,9 +1846,10 @@ static struct aa_profile *fqlookupn_profile(struct aa_label *base,
 }
 
 /**
- * aa_label_parse - parse, validate and convert a text string to a label
+ * aa_label_strn_parse - parse, validate and convert a text string to a label
  * @base: base label to use for lookups (NOT NULL)
  * @str: null terminated text string (NOT NULL)
+ * @n: length of str to parse, will stop at \0 if encountered before n
  * @gfp: allocation type
  * @create: true if should create compound labels if they don't exist
  * @force_stack: true if should stack even if no leading &
@@ -1855,19 +1857,23 @@ static struct aa_profile *fqlookupn_profile(struct aa_label *base,
  * Returns: the matching refcounted label if present
  *     else ERRPTR
  */
-struct aa_label *aa_label_parse(struct aa_label *base, const char *str,
-				gfp_t gfp, bool create, bool force_stack)
+struct aa_label *aa_label_strn_parse(struct aa_label *base, const char *str,
+				     size_t n, gfp_t gfp, bool create,
+				     bool force_stack)
 {
 	DEFINE_VEC(profile, vec);
 	struct aa_label *label, *currbase = base;
 	int i, len, stack = 0, error;
+	const char *end = str + n;
 	const char *split;
 
 	AA_BUG(!base);
 	AA_BUG(!str);
 
-	str = skip_spaces(str);
-	len = label_count_str_entries(str);
+	str = skipn_spaces(str, n);
+	if (str == NULL)
+		return ERR_PTR(-EINVAL);
+	len = label_count_strn_entries(str, end - str);
 	if (*str == '&' || force_stack) {
 		/* stack on top of base */
 		stack = base->size;
@@ -1885,7 +1891,7 @@ struct aa_label *aa_label_parse(struct aa_label *base, const char *str,
 	for (i = 0; i < stack; i++)
 		vec[i] = aa_get_profile(base->vec[i]);
 
-	for (split = aa_label_str_split(str), i = stack;
+	for (split = aa_label_strn_split(str, end - str), i = stack;
 	     split && i < len; i++) {
 		vec[i] = fqlookupn_profile(base, currbase, str, split - str);
 		if (!vec[i])
@@ -1897,11 +1903,11 @@ struct aa_label *aa_label_parse(struct aa_label *base, const char *str,
 		if (vec[i]->ns != labels_ns(currbase))
 			currbase = &vec[i]->label;
 		str = split + 3;
-		split = aa_label_str_split(str);
+		split = aa_label_strn_split(str, end - str);
 	}
 	/* last element doesn't have a split */
 	if (i < len) {
-		vec[i] = fqlookupn_profile(base, currbase, str, strlen(str));
+		vec[i] = fqlookupn_profile(base, currbase, str, end - str);
 		if (!vec[i])
 			goto fail;
 	}
@@ -1933,6 +1939,13 @@ struct aa_label *aa_label_parse(struct aa_label *base, const char *str,
 	goto out;
 }
 
+struct aa_label *aa_label_parse(struct aa_label *base, const char *str,
+				gfp_t gfp, bool create, bool force_stack)
+{
+	return aa_label_strn_parse(base, str, strlen(str), gfp, create,
+				   force_stack);
+}
+
 /**
  * aa_labelset_destroy - remove all labels from the label set
  * @ls: label set to cleanup (NOT NULL)