Resolve path while creating executable

snap/snapcraft.yaml

@@ -1,6 +1,6 @@
 name: suid-wrapper
 base: core20
-version: '0.1.3'
+version: '0.1.4'
 summary: Utility to create binary executables to be used with the suid flag
 description: |
   This utility lets you create an executable binary, with the suid flag set.
@@ -29,6 +29,6 @@ parts:
     build-packages:
       - make
     override-build: |
-      APP_VERSION=0.1.3 make release
+      APP_VERSION=0.1.4 make release
       mkdir -p $SNAPCRAFT_PART_INSTALL/bin
       cp bin/release/suid-wrapper $SNAPCRAFT_PART_INSTALL/bin/suid-wrapper

src/linker.c

@@ -190,6 +190,12 @@ static int generate_binary(struct arguments arguments)
 	{
 		return 1;
 	}
+	char resolved_path[PATH_MAX];
+    if (realpath(wrapper->argv[0], resolved_path) == NULL)
+    {
+        log_error("Unable to locate executable at \"%s\".\nPlease provide the absolute path to the binary.\n", wrapper->argv[0]);
+        return 1;
+    }
 
 	char marker[] = APP_NAME;
 	fwrite(marker, sizeof(marker), 1, output);
@@ -219,13 +225,27 @@ static int generate_binary(struct arguments arguments)
 
 static wrapper *wrapper_build_from_args(struct arguments arguments)
 {
+    if (arguments.argc < 1)
+    {
+        log_error("Invalid arguments for wrapper_build_from_args");
+        return NULL;
+    }
+
 	wrapper *result = wrapper_new(arguments.argc);
 	if (result == NULL)
 	{
 		return NULL;
 	}
 
-	for (int i = 0; i < result->argc; i++)
+    result->argv[0] = realpath(arguments.argv[0], NULL);
+    if (result->argv[0] == NULL)
+    {
+        log_error("Failed to resolve path to \"%s\".\n", arguments.argv[0]);
+        wrapper_destroy(result);
+        return NULL;
+    }
+
+	for (int i = 1; i < result->argc; i++)
 	{
 		argv_len_t len = strlen(arguments.argv[i]);
 		result->argv[i] = (char *)malloc(sizeof(char) * (len + 1));

src/runner.c

@@ -1,6 +1,8 @@
 #define _XOPEN_SOURCE 500
 
 #include <unistd.h>
+#include <errno.h>
+#include <string.h>
 #include <stdio.h>
 #include <stdint.h>
 #include "wrapper.h"
@@ -45,7 +47,12 @@ int main(int argc, char **argv)
 	}
 
 	char *new_env[] = { NULL };
-	execve(new_argv[0], &new_argv[0], new_env);
+	int result = execve(new_argv[0], &new_argv[0], new_env);
+    if (result != 0)
+    {
+        fprintf(stderr, "Failed to execute program %s:\n\t%s", new_argv[0], strerror(errno));
+        return 1;
+    }
 	wrapper_destroy(wrapper);
 
 	return 0;

src/wrapper.c

@@ -1,38 +1,23 @@
 #define _XOPEN_SOURCE 500
 
-#include <unistd.h>
 #include <inttypes.h>
 #include <linux/limits.h>
 #include <string.h>
-#include <malloc.h>
-#include <stdbool.h>
 #include <stdarg.h>
+#include <stdlib.h>
 #include "wrapper.h"
 
 const uint64_t MAX_MEMORY = 5 * 1024 * 1024;
 
 FILE *open_exe(const char *path)
 {
-	char path1[PATH_MAX];
-	char path2[PATH_MAX];
-	char *current_path = path1;
-	char *next_path = path2;
-	strncpy(current_path, path, PATH_MAX - 1);
-	current_path[PATH_MAX - 1] = 0;
-
-	ssize_t path_len = readlink(current_path, next_path, PATH_MAX);
-	while (path_len > 0)
-	{
-		log_debug("Following symlink %s...\n", current_path);
-		next_path[path_len] = 0;
-		char *temp = current_path;
-		current_path = next_path;
-		next_path = temp;
-		path_len = readlink(current_path, next_path, PATH_MAX) != -1;
-	}
-	log_debug("Executable found in %s.\n", current_path);
+	char resolved_path[PATH_MAX];
+    if (realpath(path, resolved_path) == NULL)
+    {
+        return NULL;
+    }
 
-	return fopen(current_path, "r");
+	return fopen(resolved_path, "r");
 }
 
 wrapper *wrapper_new(int argc)