[PATCH v2] libsepol/cil: Validate conditional expressions before adding to binary policy

* [PATCH v2] libsepol/cil: Validate conditional expressions before adding to binary policy
@ 2020-09-09 20:57 James Carter
  2020-09-10 12:37 ` Stephen Smalley
  0 siblings, 1 reply; 3+ messages in thread
From: James Carter @ 2020-09-09 20:57 UTC (permalink / raw)
  To: selinux; +Cc: James Carter

CIL was not correctly determining the depth of conditional expressions
which prevented it from giving an error when the max depth was exceeded.
This allowed invalid policy binaries to be created.

Validate the conditional expression using the same logic that is used
when evaluating a conditional expression. This includes checking the
depth of the expression.

Signed-off-by: James Carter <jwcart2@gmail.com>
---
v2 changes:
Return SEPOL_ERR or SEPOL_OK
Return SEPOL_OK if cond expr is valid
Return SEPOL_ERR if depth != 0 at the end

 libsepol/cil/src/cil_binary.c    | 50 ++++++++++++++++++++++++++++++++
 libsepol/cil/src/cil_build_ast.c | 26 +++++------------
 2 files changed, 57 insertions(+), 19 deletions(-)

diff --git a/libsepol/cil/src/cil_binary.c b/libsepol/cil/src/cil_binary.c
index 77266858..8575c3b1 100644
--- a/libsepol/cil/src/cil_binary.c
+++ b/libsepol/cil/src/cil_binary.c
@@ -2176,6 +2176,51 @@ static int __cil_cond_expr_to_sepol_expr(policydb_t *pdb, struct cil_list *cil_e
 	return SEPOL_OK;
 }
 
+int __cil_validate_cond_expr(cond_expr_t *cond_expr)
+{
+	cond_expr_t *e;
+	int depth = -1;
+
+	for (e = cond_expr; e != NULL; e = e->next) {
+		switch (e->expr_type) {
+		case COND_BOOL:
+			if (depth == (COND_EXPR_MAXDEPTH - 1)) {
+				cil_log(CIL_ERR,"Conditional expression exceeded max allowable depth\n");
+				return SEPOL_ERR;
+			}
+			depth++;
+			break;
+		case COND_NOT:
+			if (depth < 0) {
+				cil_log(CIL_ERR,"Invalid conditional expression\n");
+				return SEPOL_ERR;
+			}
+			break;
+		case COND_OR:
+		case COND_AND:
+		case COND_XOR:
+		case COND_EQ:
+		case COND_NEQ:
+			if (depth < 1) {
+				cil_log(CIL_ERR,"Invalid conditional expression\n");
+				return SEPOL_ERR;
+			}
+			depth--;
+			break;
+		default:
+			cil_log(CIL_ERR,"Invalid conditional expression\n");
+			return SEPOL_ERR;
+		}
+	}
+
+	if (depth != 0) {
+		cil_log(CIL_ERR,"Invalid conditional expression\n");
+		return SEPOL_ERR;
+	}
+
+	return SEPOL_OK;
+}
+
 int cil_booleanif_to_policydb(policydb_t *pdb, const struct cil_db *db, struct cil_tree_node *node)
 {
 	int rc = SEPOL_ERR;
@@ -2204,6 +2249,11 @@ int cil_booleanif_to_policydb(policydb_t *pdb, const struct cil_db *db, struct c
 		goto exit;
 	}
 
+	rc = __cil_validate_cond_expr(tmp_cond->expr);
+	if (rc != SEPOL_OK) {
+		goto exit;
+	}
+
 	tmp_cond->true_list = &tmp_cl;
 
 	rc = cond_normalize_expr(pdb, tmp_cond);
diff --git a/libsepol/cil/src/cil_build_ast.c b/libsepol/cil/src/cil_build_ast.c
index 60ecaaff..f1d5dcca 100644
--- a/libsepol/cil/src/cil_build_ast.c
+++ b/libsepol/cil/src/cil_build_ast.c
@@ -2548,18 +2548,13 @@ static enum cil_flavor __cil_get_expr_operator_flavor(const char *op)
 	else return CIL_NONE;
 }
 
-static int __cil_fill_expr(struct cil_tree_node *current, enum cil_flavor flavor, struct cil_list *expr, int *depth);
+static int __cil_fill_expr(struct cil_tree_node *current, enum cil_flavor flavor, struct cil_list *expr);
 
-static int __cil_fill_expr_helper(struct cil_tree_node *current, enum cil_flavor flavor, struct cil_list *expr, int *depth)
+static int __cil_fill_expr_helper(struct cil_tree_node *current, enum cil_flavor flavor, struct cil_list *expr)
 {
 	int rc = SEPOL_ERR;
 	enum cil_flavor op;
 
-	if (flavor == CIL_BOOL && *depth > COND_EXPR_MAXDEPTH) {
-		cil_log(CIL_ERR, "Max depth of %d exceeded for boolean expression\n", COND_EXPR_MAXDEPTH);
-		goto exit;
-	}
-
 	op = __cil_get_expr_operator_flavor(current->data);
 
 	rc = cil_verify_expr_syntax(current, op, flavor);
@@ -2572,26 +2567,20 @@ static int __cil_fill_expr_helper(struct cil_tree_node *current, enum cil_flavor
 		current = current->next;
 	}
 
-	if (op == CIL_NONE || op == CIL_ALL) {
-		(*depth)++;
-	}
-
 	for (;current != NULL; current = current->next) {
-		rc = __cil_fill_expr(current, flavor, expr, depth);
+		rc = __cil_fill_expr(current, flavor, expr);
 		if (rc != SEPOL_OK) {
 			goto exit;
 		}
 	}
 
-	(*depth)--;
-
 	return SEPOL_OK;
 
 exit:
 	return rc;
 }
 
-static int __cil_fill_expr(struct cil_tree_node *current, enum cil_flavor flavor, struct cil_list *expr, int *depth)
+static int __cil_fill_expr(struct cil_tree_node *current, enum cil_flavor flavor, struct cil_list *expr)
 {
 	int rc = SEPOL_ERR;
 
@@ -2605,7 +2594,7 @@ static int __cil_fill_expr(struct cil_tree_node *current, enum cil_flavor flavor
 	} else {
 		struct cil_list *sub_expr;
 		cil_list_init(&sub_expr, flavor);
-		rc = __cil_fill_expr_helper(current->cl_head, flavor, sub_expr, depth);
+		rc = __cil_fill_expr_helper(current->cl_head, flavor, sub_expr);
 		if (rc != SEPOL_OK) {
 			cil_list_destroy(&sub_expr, CIL_TRUE);
 			goto exit;
@@ -2623,14 +2612,13 @@ exit:
 int cil_gen_expr(struct cil_tree_node *current, enum cil_flavor flavor, struct cil_list **expr)
 {
 	int rc = SEPOL_ERR;
-	int depth = 0;
 
 	cil_list_init(expr, flavor);
 
 	if (current->cl_head == NULL) {
-		rc = __cil_fill_expr(current, flavor, *expr, &depth);
+		rc = __cil_fill_expr(current, flavor, *expr);
 	} else {
-		rc = __cil_fill_expr_helper(current->cl_head, flavor, *expr, &depth);
+		rc = __cil_fill_expr_helper(current->cl_head, flavor, *expr);
 	}
 
 	if (rc != SEPOL_OK) {
-- 
2.25.4


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