[PATCH] libselinux: fix string conversion of unknown perms

[Mike Palmiotto <mike.palmiotto@xxxxxxxxxxxxxxx>]

Commit c19395d72295f5e69275d98df5db22dfdf214b6c fixed some handling of unknown
classes/permissions, but missed the case where an unknown permission is loaded
and then subsequently logged, either via denial or auditallow. If a permission
set has some valid values mixed with unknown values, say `{ read write foo }`,
a check on `{ read write foo }` would fail to log the entire set.

To fix this, skip over the bad permissions/classes when expanding them to
strings. The unknowns should be logged during `selinux_set_mapping`, so
there is no need for further logging of the actual unknown permissions.

Signed-off-by: Mike Palmiotto <mike.palmiotto@xxxxxxxxxxxxxxx>
---
 libselinux/src/stringrep.c | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/libselinux/src/stringrep.c b/libselinux/src/stringrep.c
index ad29f76d..85579422 100644
--- a/libselinux/src/stringrep.c
+++ b/libselinux/src/stringrep.c
@@ -276,19 +276,15 @@ int security_av_string(security_class_t tclass, access_vector_t av, char **res)
 	char *ptr;
 
 	/* first pass computes the required length */
-	while (tmp) {
+	for (i = 0; tmp; tmp >>= 1, i++) {
 		if (tmp & 1) {
 			str = security_av_perm_to_string(tclass, av & (1<<i));
-			if (str)
-				len += strlen(str) + 1;
-			else {
-				rc = -1;
-				errno = EINVAL;
-				goto out;
+			if (!str) {
+				continue;
 			}
+
+			len += strlen(str) + 1;
 		}
-		tmp >>= 1;
-		i++;
 	}
 
 	*res = malloc(len);
@@ -298,7 +294,6 @@ int security_av_string(security_class_t tclass, access_vector_t av, char **res)
 	}
 
 	/* second pass constructs the string */
-	i = 0;
 	tmp = av;
 	ptr = *res;
 
@@ -308,12 +303,13 @@ int security_av_string(security_class_t tclass, access_vector_t av, char **res)
 	}
 
 	ptr += sprintf(ptr, "{ ");
-	while (tmp) {
-		if (tmp & 1)
-			ptr += sprintf(ptr, "%s ", security_av_perm_to_string(
-					       tclass, av & (1<<i)));
-		tmp >>= 1;
-		i++;
+	for (i = 0; tmp; tmp >>= 1, i++) {
+		if (tmp & 1) {
+			str = security_av_perm_to_string(tclass, av & (1<<i));
+			if (str) {
+				ptr += sprintf(ptr, "%s ", str);
+			}
+		}
 	}
 	sprintf(ptr, "}");
 out:
-- 
2.21.0