Safely quote all variable expansions.

When expanding a variable set by a message from the kernel, safely
quote all arguments expanded when creating a command line for the
shell.

Reviewd by: Shawn Webb, Oliver Pinter, brd@
Sponsored by: Netflix

sbin/devd/devd.cc

@@ -636,6 +636,30 @@ config::is_id_char(char ch) const
 	    ch == '-'));
 }
 
+string
+config::shell_quote(const string &s)
+{
+	string buffer;
+
+	/*
+	 * Enclose the string in $' ' with escapes for ' and / characters making
+	 * it one argument and ensuring the shell won't be affected by its
+	 * usual list of candidates.
+	 */
+	buffer.reserve(s.length() * 3 / 2);
+	buffer += '$';
+	buffer += '\'';
+	for (const char &c : s) {
+		if (c == '\'' || c == '\\') {
+			buffer += '\\';
+		}
+		buffer += c;
+	}
+	buffer += '\'';
+
+	return buffer;
+}
+
 void
 config::expand_one(const char *&src, string &dst)
 {
@@ -650,8 +674,7 @@ config::expand_one(const char *&src, string &dst)
 	}
 
 	// $(foo) -> $(foo)
-	// Not sure if I want to support this or not, so for now we just pass
-	// it through.
+	// This is the escape hatch for passing down shell subcommands
 	if (*src == '(') {
 		dst += '$';
 		count = 1;
@@ -677,7 +700,7 @@ config::expand_one(const char *&src, string &dst)
 	do {
 		buffer += *src++;
 	} while (is_id_char(*src));
-	dst.append(get_variable(buffer));
+	dst.append(shell_quote(get_variable(buffer)));
 }
 
 const string

sbin/devd/devd.hh

@@ -173,6 +173,7 @@ protected:
 	void parse_one_file(const char *fn);
 	void parse_files_in_dir(const char *dirname);
 	void expand_one(const char *&src, std::string &dst);
+	std::string shell_quote(const std::string &s);
 	bool is_id_char(char) const;
 	bool chop_var(char *&buffer, char *&lhs, char *&rhs) const;
 private: