[PATCH 4/6] libsepol/cil: fix NULL pointer dereference when parsing an improper integer

[Nicolas Iooss <nicolas.iooss@xxxxxxx>]

OSS-Fuzz found a NULL pointer dereference when the CIL compiler tries to
compile a policy with an invalid integer:

    $ echo '(ioportcon(2())n)' > tmp.cil
    $ secilc tmp.cil
    Segmentation fault (core dumped)

This is because strtol() is called with a NULL pointer, in
cil_fill_integer().

Fix this by checking that int_node->data is not NULL. While at it, use
strtoul() instead of strtol() to parse an unsigned integer.

Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=28456
Signed-off-by: Nicolas Iooss <nicolas.iooss@xxxxxxx>
---
 libsepol/cil/src/cil_build_ast.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/libsepol/cil/src/cil_build_ast.c b/libsepol/cil/src/cil_build_ast.c
index 67801def0dc0..0c9015cef578 100644
--- a/libsepol/cil/src/cil_build_ast.c
+++ b/libsepol/cil/src/cil_build_ast.c
@@ -5566,15 +5566,15 @@ int cil_fill_integer(struct cil_tree_node *int_node, uint32_t *integer, int base
 {
 	int rc = SEPOL_ERR;
 	char *endptr = NULL;
-	int val;
+	unsigned long val;
 
-	if (int_node == NULL || integer == NULL) {
+	if (int_node == NULL || int_node->data == NULL || integer == NULL) {
 		goto exit;
 	}
 
 	errno = 0;
-	val = strtol(int_node->data, &endptr, base);
-	if (errno != 0 || endptr == int_node->data || *endptr != '\0') {
+	val = strtoul(int_node->data, &endptr, base);
+	if (errno != 0 || endptr == int_node->data || *endptr != '\0' || val > UINT32_MAX) {
 		rc = SEPOL_ERR;
 		goto exit;
 	}
@@ -5594,7 +5594,7 @@ int cil_fill_integer64(struct cil_tree_node *int_node, uint64_t *integer, int ba
 	char *endptr = NULL;
 	uint64_t val;
 
-	if (int_node == NULL || integer == NULL) {
+	if (int_node == NULL || int_node->data == NULL || integer == NULL) {
 		goto exit;
 	}
 
-- 
2.29.2