On Linux execve() can be called with a NULL argv, which results in
argc being set to zero and an empty list for argv. Doing so causes the
polkit applications to misbehave, for example:

  $ python
  >>> import os
  >>> os.execve("/usr/bin/pkexec", [], {"FOO":"aaaaaaaaa"})
  Cannot run program FOO=aaaaaaaaa: No such file or directory

While this doesn't appear to have an further impact, setuid binaries
should be hardened against any possible misuse. Add an explicit check
for argc == 0 to all of the polkit applications.

Signed-off-by: Ryan Mallon <rmallon@gmail.com>
---

 src/programs/pkaction.c   |   10 ++++++++++
 src/programs/pkcheck.c    |   10 ++++++++++
 src/programs/pkexec.c     |   10 ++++++++++
 src/programs/pkttyagent.c |   10 ++++++++++
 4 files changed, 40 insertions(+)

diff --git a/src/programs/pkaction.c b/src/programs/pkaction.c
index f17a7dc..1034a82 100644
--- a/src/programs/pkaction.c
+++ b/src/programs/pkaction.c
@@ -121,6 +121,16 @@ main (int argc, char *argv[])
   actions = NULL;
   ret = 1;

+  /*
+   * Linux allows an empty list to be passed for argv. This is a non-standard
+   * (mis)feature, so don't allow it.
+   */
+  if (argc == 0)
+    {
+      g_printerr("Refusing to accept empty argv\n");
+      goto out;
+    }
+
   g_type_init ();

   opt_show_version = FALSE;
diff --git a/src/programs/pkcheck.c b/src/programs/pkcheck.c
index 5781893..c2352e3 100644
--- a/src/programs/pkcheck.c
+++ b/src/programs/pkcheck.c
@@ -362,6 +362,16 @@ main (int argc, char *argv[])
   local_agent_handle = NULL;
   ret = 126;

+  /*
+   * Linux allows an empty list to be passed for argv. This is a non-standard
+   * (mis)feature, so don't allow it.
+   */
+  if (argc == 0)
+    {
+      g_printerr("Refusing to accept empty argv\n");
+      goto out;
+    }
+
   g_type_init ();

   details = polkit_details_new ();
diff --git a/src/programs/pkexec.c b/src/programs/pkexec.c
index a7ca8e0..88363c0 100644
--- a/src/programs/pkexec.c
+++ b/src/programs/pkexec.c
@@ -502,6 +502,16 @@ main (int argc, char *argv[])
   opt_user = NULL;
   local_agent_handle = NULL;

+  /*
+   * Linux allows an empty list to be passed for argv. This is a non-standard
+   * (mis)feature, so don't allow it.
+   */
+  if (argc == 0)
+    {
+      g_printerr("Refusing to accept empty argv\n");
+      goto out;
+    }
+
   /* check for correct invocation */
   if (geteuid () != 0)
     {
diff --git a/src/programs/pkttyagent.c b/src/programs/pkttyagent.c
index 423b728..ed3caa5 100644
--- a/src/programs/pkttyagent.c
+++ b/src/programs/pkttyagent.c
@@ -74,6 +74,16 @@ main (int argc, char *argv[])
   guint ret = 126;
   GVariantBuilder builder;

+  /*
+   * Linux allows an empty list to be passed for argv. This is a non-standard
+   * (mis)feature, so don't allow it.
+   */
+  if (argc == 0)
+    {
+      g_printerr("Refusing to accept empty argv\n");
+      goto out;
+    }
+
   g_type_init ();

   error = NULL;
--
1.7.9.7