From 001b21871c61e3a13a949173e429f86ea362959d Mon Sep 17 00:00:00 2001
From: Erich Eckner <git@eckner.net>
Date: Mon, 23 Oct 2017 12:29:37 +0200
Subject: bin/slave-build-connect: repair, but still preven shell injections

---
 bin/slave-build-connect | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/bin/slave-build-connect b/bin/slave-build-connect
index e773256..84abba1 100755
--- a/bin/slave-build-connect
+++ b/bin/slave-build-connect
@@ -5,13 +5,21 @@
 
 if [ "${SSH_ORIGINAL_COMMAND%% *}" = "get-assignment" ] || \
   [ "${SSH_ORIGINAL_COMMAND%% *}" = "return-assignment" ]; then
-  export slave="$1"
-  # this is somewhat cumbersome, but we want:
-  #  - no expansion of special shell-chars (*,;,\n,&&,~,$HOME)
-  #  - splitting of arguments on spaces
-  echo "${SSH_ORIGINAL_COMMAND#* }" | \
-    xargs "${base_dir}/bin/${SSH_ORIGINAL_COMMAND%% *}"
+
+  # small check to prevent some shell-injections
+  if echo "${SSH_ORIGINAL_COMMAND}" | \
+    grep -q '[^-a-zA-Z0-9.+_]'; then
+
+    >&2 printf 'Invalid command: "%s".\n' "${SSH_ORIGINAL_COMMAND}"
+    exit 42
+
+  fi
+
+  slave="$1" /bin/sh -c "${base_dir}/bin/${SSH_ORIGINAL_COMMAND}"
+
 else
-  >&2 echo "Invalid command: '${SSH_ORIGINAL_COMMAND%% *}'"
+
+  >&2 printf 'Invalid command: "%s".\n' "${SSH_ORIGINAL_COMMAND}"
   exit 42
+
 fi
-- 
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