[v3] checkpolicy: Fix MLS users in optional blocks

Commit Message

James Carter Aug. 28, 2024, 3:15 p.m. UTC

When a user is created in an optional block, a user datum is added
to both the avrule_decl's symtab and the policydb's symtab, but
the semantic MLS information is only added to the avrule_decl's
user datum. This causes an error to occur during policy expansion
when user_copy_callback() is called. If this error did not occur
then the policydb's user datum would be written without any MLS
info and the policy would fail validation when read later.

When creating a user datum, search for a user datum with the same
key in the policydb's symtab. If that datum has no MLS information,
then copy the MLS information from the avrule_decl's datum. If it
does, then compare the default level, low level, and high level
sensitivities and give an error if they do not match. There is not
enough information to expand the categories for the high and low
levels, so merge the semantic categories. If the two category sets
are not equal an error will occur during the expansion phase.

A minimum policy to demonstrate the bug:
class CLASS1
sid kernel
class CLASS1 { PERM1 }
sensitivity SENS1;
dominance { SENS1 }
level SENS1;
mlsconstrain CLASS1 { PERM1 } ((h1 dom h2) and (l1 domby h1));
type TYPE1;
allow TYPE1 self : CLASS1 PERM1;
role ROLE1;
role ROLE1 types TYPE1;
optional {
  require {
    role ROLE1;
  }
  user USER2 roles ROLE1 level SENS1 range SENS1;
}
user USER1 roles ROLE1 level SENS1 range SENS1;
sid kernel USER1:ROLE1:TYPE1:SENS1

Signed-off-by: James Carter <[e-mail]>
---
v2:
  - Fixed mls_semantic_cats_merge() so that it keeps existing cats in dst
  - Made src const in mls_add_or_check_level()
v3:
  - Free id in the error path

 checkpolicy/policy_define.c | 72 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 71 insertions(+), 1 deletion(-)

Patch

diff --git a/checkpolicy/policy_define.c b/checkpolicy/policy_define.c
index bfeda86b..af8d007c 100644
--- a/checkpolicy/policy_define.c
+++ b/checkpolicy/policy_define.c
@@ -4175,6 +4175,50 @@  static int parse_categories(char *id, level_datum_t * levdatum, ebitmap_t * cats
 	return 0;
 }
 
+static int mls_semantic_cats_merge(mls_semantic_cat_t ** dst,
+								   const mls_semantic_cat_t * src)
+{
+	mls_semantic_cat_t *new;
+
+	while (src) {
+		new = (mls_semantic_cat_t *) malloc(sizeof(mls_semantic_cat_t));
+		if (!new)
+			return -1;
+
+		mls_semantic_cat_init(new);
+		new->low = src->low;
+		new->high = src->high;
+		new->next = *dst;
+		*dst = new;
+
+		src = src->next;
+	}
+
+	return 0;
+}
+
+static int mls_add_or_check_level(mls_semantic_level_t *dst, const mls_semantic_level_t *src)
+{
+	if (!dst->sens) {
+		if (mls_semantic_level_cpy(dst, src) < 0) {
+			yyerror("out of memory");
+			return -1;
+		}
+	} else {
+		if (dst->sens != src->sens) {
+			return -1;
+		}
+		/* Duplicate cats won't cause problems, but different cats will
+		 * result in an error during expansion */
+		if (mls_semantic_cats_merge(&dst->cat, src->cat) < 0) {
+			yyerror("out of memory");
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
 static int parse_semantic_categories(char *id, level_datum_t * levdatum __attribute__ ((unused)),
 				     mls_semantic_cat_t ** cats)
 {
@@ -4233,7 +4277,7 @@  static int parse_semantic_categories(char *id, level_datum_t * levdatum __attrib
 int define_user(void)
 {
 	char *id;
-	user_datum_t *usrdatum;
+	user_datum_t *usrdatum, *usr_global;
 	level_datum_t *levdatum;
 	int l;
 
@@ -4258,10 +4302,16 @@  int define_user(void)
 		return 0;
 	}
 
+	id = strdup(queue_head(id_queue));
+
 	if ((usrdatum = declare_user()) == NULL) {
+		free(id);
 		return -1;
 	}
 
+	usr_global = hashtab_search(policydbp->p_users.table, (hashtab_key_t) id);
+	free(id);
+
 	while ((id = queue_remove(id_queue))) {
 		if (set_user_roles(&usrdatum->roles, id))
 			return -1;
@@ -4288,6 +4338,7 @@  int define_user(void)
 		usrdatum->dfltlevel.sens = levdatum->level->sens;
 
 		while ((id = queue_remove(id_queue))) {
+			/* This will add to any already existing categories */
 			if (parse_semantic_categories(id, levdatum,
 			                            &usrdatum->dfltlevel.cat)) {
 				free(id);
@@ -4313,6 +4364,7 @@  int define_user(void)
 			usrdatum->range.level[l].sens = levdatum->level->sens;
 
 			while ((id = queue_remove(id_queue))) {
+				/* This will add to any already existing categories */
 				if (parse_semantic_categories(id, levdatum,
 				               &usrdatum->range.level[l].cat)) {
 					free(id);
@@ -4333,6 +4385,24 @@  int define_user(void)
 				return -1;
 			}
 		}
+
+		if (usr_global && usr_global != usrdatum) {
+			if (mls_add_or_check_level(&usr_global->dfltlevel,
+									   &usrdatum->dfltlevel)) {
+				yyerror("Problem with user default level");
+				return -1;
+			}
+			if (mls_add_or_check_level(&usr_global->range.level[0],
+									   &usrdatum->range.level[0])) {
+				yyerror("Problem with user low level");
+				return -1;
+			}
+			if (mls_add_or_check_level(&usr_global->range.level[1],
+									   &usrdatum->range.level[1])) {
+				yyerror("Problem with user high level");
+				return -1;
+			}
+		}
 	}
 	return 0;
 }