Fix handling of mmap failure and mapping empty files

Check the return value of mmap() correctly.

Empty files cannot be mmap'd so we implement some
work around code for that.

https://bugs.freedesktop.org/show_bug.cgi?id=74773

Signed-off-by: Stef Walter <stef@thewalter.net>

2 files changed, 26 insertions, 2 deletions

diff --git a/common/compat.c b/common/compat.c
index 9aa556a..f5b88ec 100644
--- a/common/compat.c
+++ b/common/compat.c
@@ -216,9 +216,15 @@ p11_mmap_open (const char *path,
 		return NULL;
 	}
 
+	if (sb->st_size == 0) {
+		*data = "";
+		*size = 0;
+		return map;
+	}
+
 	map->size = sb->st_size;
 	map->data = mmap (NULL, map->size, PROT_READ, MAP_PRIVATE, map->fd, 0);
-	if (map->data == NULL) {
+	if (map->data == MAP_FAILED) {
 		close (map->fd);
 		free (map);
 		return NULL;
@@ -232,7 +238,8 @@ p11_mmap_open (const char *path,
 void
 p11_mmap_close (p11_mmap *map)
 {
-	munmap (map->data, map->size);
+	if (map->size)
+		munmap (map->data, map->size);
 	close (map->fd);
 	free (map);
 }
diff --git a/common/tests/test-compat.c b/common/tests/test-compat.c
index 872170d..42471ae 100644
--- a/common/tests/test-compat.c
+++ b/common/tests/test-compat.c
@@ -83,6 +83,22 @@ test_getauxval (void)
 	free (path);
 }
 
+static void
+test_mmap (void)
+{
+	p11_mmap *map;
+	void *data;
+	size_t size;
+	char file[] = "emptyfileXXXXXX";
+	int fd = mkstemp (file);
+	close (fd);
+	/* mmap on empty file should work */
+	map = p11_mmap_open (file, NULL, &data, &size);
+	unlink (file);
+	assert_ptr_not_null (map);
+	p11_mmap_close (map);
+}
+
 #endif /* OS_UNIX */
 
 int
@@ -95,6 +111,7 @@ main (int argc,
 	if (!getenv ("FAKED_MODE")) {
 		p11_test (test_getauxval, "/compat/getauxval");
 	}
+	p11_test (test_mmap, "/compat/mmap");
 #endif
 	return p11_test_run (argc, argv);
 }