[PATCH v3 3/3] depmod: shut up gcc insufficinet buffer warning.

[Michal Suchanek <msuchanek@xxxxxxx>]

In a couple of places depmod concatenates the module directory and
filename with snprintf. This can technically overflow creating wrong
path if module directory name is long. Use openat instead as is done
elsewhere in depmod. This avoids the snprintf, the extra buffer on
stack, and the gcc warning.

Signed-off-by: Michal Suchanek <msuchanek@xxxxxxx>
---
v3:
 - remove superfluous whitespace
---
 tools/depmod.c | 51 ++++++++++++++++++++++++++++++++++----------------
 1 file changed, 35 insertions(+), 16 deletions(-)

diff --git a/tools/depmod.c b/tools/depmod.c
index 0f7e33ccfd59..0cf845a0dbc7 100644
--- a/tools/depmod.c
+++ b/tools/depmod.c
@@ -1389,19 +1389,42 @@ static int depmod_modules_build_array(struct depmod *depmod)
 	return 0;
 }
 
+static FILE *dfdopen(const char *dname, const char *filename, int flags, const char *mode)
+{
+	int fd, dfd;
+	FILE *ret;
+
+	dfd = open(dname, O_RDONLY);
+	if (dfd < 0) {
+		WRN("could not open directory %s: %m\n", dname);
+		return NULL;
+	}
+
+	fd = openat(dfd, filename, flags);
+	if (fd < 0) {
+		WRN("could not open %s at %s: %m\n", filename, dname);
+		ret = NULL;
+	} else {
+		ret = fdopen(fd, mode);
+		if (!ret)
+			WRN("could not associate stream with %s: %m\n", filename);
+	}
+	close(dfd);
+	return ret;
+}
+
+
+
 static void depmod_modules_sort(struct depmod *depmod)
 {
-	char order_file[PATH_MAX], line[PATH_MAX];
+	char line[PATH_MAX];
+	const char * order_file = "modules.order";
 	FILE *fp;
 	unsigned idx = 0, total = 0;
 
-	snprintf(order_file, sizeof(order_file), "%s/modules.order",
-		 depmod->cfg->dirname);
-	fp = fopen(order_file, "r");
-	if (fp == NULL) {
-		WRN("could not open %s: %m\n", order_file);
+	fp = dfdopen(depmod->cfg->dirname, order_file, O_RDONLY, "r");
+	if (fp == NULL)
 		return;
-	}
 
 	while (fgets(line, sizeof(line), fp) != NULL) {
 		size_t len = strlen(line);
@@ -1409,8 +1432,8 @@ static void depmod_modules_sort(struct depmod *depmod)
 		if (len == 0)
 			continue;
 		if (line[len - 1] != '\n') {
-			ERR("%s:%u corrupted line misses '\\n'\n",
-				order_file, idx);
+			ERR("%s/%s:%u corrupted line misses '\\n'\n",
+				depmod->cfg->dirname, order_file, idx);
 			goto corrupted;
 		}
 	}
@@ -2287,18 +2310,14 @@ static int output_builtin_bin(struct depmod *depmod, FILE *out)
 {
 	FILE *in;
 	struct index_node *idx;
-	char infile[PATH_MAX], line[PATH_MAX], modname[PATH_MAX];
+	char line[PATH_MAX], modname[PATH_MAX];
 
 	if (out == stdout)
 		return 0;
 
-	snprintf(infile, sizeof(infile), "%s/modules.builtin",
-							depmod->cfg->dirname);
-	in = fopen(infile, "r");
-	if (in == NULL) {
-		WRN("could not open %s: %m\n", infile);
+	in = dfdopen(depmod->cfg->dirname, "modules.builtin", O_RDONLY, "r");
+	if (in == NULL)
 		return 0;
-	}
 
 	idx = index_create();
 	if (idx == NULL) {
-- 
2.19.2