As of rsync 3, rsync reused the -e option to pass protocol information
from the client to the server.  We therefore cannot reject all -e
options to rsync, only ones not sent with --server or containing
something other than protocol information as an argument.

Based on work by Robert Hardy.

Debian Bug#471803

--- rssh.orig/util.c
+++ rssh/util.c
@@ -56,6 +56,7 @@
 #ifdef HAVE_LIBGEN_H
 #include <libgen.h>
 #endif /* HAVE_LIBGEN_H */
+#include <regex.h>
 
 /* LOCAL INCLUDES */
 #include "pathnames.h"
@@ -187,6 +188,33 @@
 }
 
 /*
+ * check_rsync_e() - take the command line passed to rssh and look for a -e
+ *                   option.  If one is found, make sure --server is provided
+ *                   and the option contains only the protocol information.
+ *                   Returns 1 if the command line is safe; 0 otherwise.
+ */
+static int check_rsync_e( char *cl )
+{
+	int	status;
+	regex_t	re;
+
+	/*
+	 * This is more complicated than it looks because we don't want to
+	 * trigger on the e in --server, but we do want to catch the common
+	 * case of -ltpre.iL (which contains -e.).
+	 */
+	static const char pattern[] = "[ \t\v\f]-([^-][^ ]*)?e[^.0-9]";
+
+	if ( strstr(cl, "--server") == NULL ) return 0;
+	if ( regcomp(&re, pattern, REG_EXTENDED | REG_NOSUB) != 0 ){
+		return 0;
+	}
+	status = regexec(&re, cl, 0, NULL, 0);
+	regfree(&re);
+	return (status == 0) ? 0 : 1;
+}
+
+/*
  * check_command_line() - take the command line passed to rssh, and verify
  * 			  that the specified command is one the user is
  * 			  allowed to run.  Return the path of the command
@@ -230,9 +258,9 @@
 
 	if ( check_command(cl, opts, PATH_RSYNC, RSSH_ALLOW_RSYNC) ){
 		/* filter -e option */
-		if ( opt_exist(cl, 'e') ){
+		if ( opt_exist(cl, 'e') && !check_rsync_e(cl) ){
 			fprintf(stderr, "\ninsecure -e option not allowed.");
-			log_msg("insecure -e option in rdist command line!");
+			log_msg("insecure -e option in rsync command line!");
 			return NULL;
 		}