apparmor: Replace sprintf/strcpy with scnprintf/strscpy in aa_policy_init

strcpy() is deprecated and sprintf() does not perform bounds checking
either. Although an overflow is unlikely, it's better to proactively
avoid it by using the safer strscpy() and scnprintf(), respectively.

Additionally, unify memory allocation for 'hname' to simplify and
improve aa_policy_init().

Closes: KSPP/linux#88
Reviewed-by: Serge Hallyn <[email protected]>
Signed-off-by: Thorsten Blum <[email protected]>
Signed-off-by: John Johansen <[email protected]>

Author: toblux

security/apparmor/lib.c

@@ -478,19 +478,17 @@ bool aa_policy_init(struct aa_policy *policy, const char *prefix,
 		    const char *name, gfp_t gfp)
 {
 	char *hname;
+	size_t hname_sz;
 
+	hname_sz = (prefix ? strlen(prefix) + 2 : 0) + strlen(name) + 1;
 	/* freed by policy_free */
-	if (prefix) {
-		hname = aa_str_alloc(strlen(prefix) + strlen(name) + 3, gfp);
-		if (hname)
-			sprintf(hname, "%s//%s", prefix, name);
-	} else {
-		hname = aa_str_alloc(strlen(name) + 1, gfp);
-		if (hname)
-			strcpy(hname, name);
-	}
+	hname = aa_str_alloc(hname_sz, gfp);
 	if (!hname)
 		return false;
+	if (prefix)
+		scnprintf(hname, hname_sz, "%s//%s", prefix, name);
+	else
+		strscpy(hname, name, hname_sz);
 	policy->hname = hname;
 	/* base.name is a substring of fqname */
 	policy->name = basename(policy->hname);