configuration: fix incorrect handling of relative executables

src/include/utils.hh

@@ -224,6 +224,12 @@ static inline uint32_t hash_block(const void *buf, size_t len)
 
 uint32_t hash_file(const std::string &filename);
 
+int find_executable(const std::string &file);
+
 // Searches for an executable named file in the directories named by the PATH
 // environment variable.
+// The named file is first tried directly without consulting PATH.
+//
+// Don't use this function when expanding the first argument of the exec()
+// family of functions, since it is insecure.
 int look_path(const std::string &file, std::string *out);

src/utils.cc

@@ -146,8 +146,9 @@ void *peek_file(size_t *out_size, const char *fmt, ...)
 	struct stat st;
 	if (lstat(path, &st) < 0)
 		return NULL;
-	// Regular file?
-	if (S_ISREG(st.st_mode) == 0)
+
+	// Not a directory?
+	if (S_ISDIR(st.st_mode) > 0)
 		return NULL;
 
 	// Read a little bit of the file    
@@ -776,8 +777,35 @@ uint32_t hash_file(const std::string &filename)
 	return out;
 }
 
+int find_executable(const std::string &file)
+{
+	struct stat st;
+
+	if (lstat(file.c_str(), &st) < 0)
+		return -1;
+
+	// Not a directory?
+	if (S_ISDIR(st.st_mode) > 0)
+		return -1;
+
+	// Executable?
+	if ((st.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH)) == 0)
+		return -1;
+
+	return 0;
+}
+
+
 int look_path(const std::string &file, std::string *out)
 {
+	// First check if the relative file is an executable.
+	if (find_executable(file) == 0)
+	{
+		*out = file;
+
+		return 0;
+	}
+
 	const char *sys_path = getenv("PATH");
 	if (!sys_path)
 		return -1;
@@ -788,22 +816,13 @@ int look_path(const std::string &file, std::string *out)
 	{
 		const std::string root = *it;
 		const std::string path = get_real_path(root + "/" + file);
-		struct stat st;
-
-		if (lstat(path.c_str(), &st) < 0)
-			continue;
 
-		// Regular file?
-		if (S_ISREG(st.st_mode) == 0)
-			continue;
-
-		// Executable?
-		if ((st.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH)) == 0)
-			continue;
-
-		*out = path;
+		if (find_executable(path) == 0)
+		{
+			*out = path;
 
-		return 0;
+			return 0;
+		}
 	}
 
 	return -1;