#

# commit a39208bd7fb76c1b01c127b4c61f9bfd915bfe7c

# Author: Carlos O'Donell <carlos@redhat.com>

# Date:   Wed Nov 19 11:44:12 2014 -0500

# 

#     CVE-2014-7817: wordexp fails to honour WRDE_NOCMD.

#     

#     The function wordexp() fails to properly handle the WRDE_NOCMD

#     flag when processing arithmetic inputs in the form of "$((... ``))"

#     where "..." can be anything valid. The backticks in the arithmetic

#     epxression are evaluated by in a shell even if WRDE_NOCMD forbade

#     command substitution. This allows an attacker to attempt to pass

#     dangerous commands via constructs of the above form, and bypass

#     the WRDE_NOCMD flag. This patch fixes this by checking for WRDE_NOCMD

#     in exec_comm(), the only place that can execute a shell. All other

#     checks for WRDE_NOCMD are superfluous and removed.

#     

#     We expand the testsuite and add 3 new regression tests of roughly

#     the same form but with a couple of nested levels.

#     

#     On top of the 3 new tests we add fork validation to the WRDE_NOCMD

#     testing. If any forks are detected during the execution of a wordexp()

#     call with WRDE_NOCMD, the test is marked as failed. This is slightly

#     heuristic since vfork might be used in the future, but it provides a

#     higher level of assurance that no shells were executed as part of

#     command substitution with WRDE_NOCMD in effect. In addition it doesn't

#     require libpthread or libdl, instead we use the public implementation

#     namespace function __register_atfork (already part of the public ABI

#     for libpthread).

#     

#     Tested on x86_64 with no regressions.

# 

diff --git glibc-2.17-c758a686/posix/wordexp-test.c glibc-2.17-c758a686/posix/wordexp-test.c

index 4957006..bdd65e4 100644

--- glibc-2.17-c758a686/posix/wordexp-test.c

+++ glibc-2.17-c758a686/posix/wordexp-test.c

@@ -27,6 +27,25 @@

 #define IFS " \n\t"

+extern void *__dso_handle __attribute__ ((__weak__, __visibility__ ("hidden")));

+extern int __register_atfork (void (*) (void), void (*) (void), void (*) (void), void *);

+

+static int __app_register_atfork (void (*prepare) (void), void (*parent) (void), void (*child) (void))

+{

+  return __register_atfork (prepare, parent, child,

+			    &__dso_handle == NULL ? NULL : __dso_handle);

+}

+

+/* Number of forks seen.  */

+static int registered_forks;

+

+/* For each fork increment the fork count.  */

+static void

+register_fork (void)

+{

+  registered_forks++;

+}

+

 struct test_case_struct

 {

   int retval;

@@ -206,6 +225,12 @@ struct test_case_struct

     { WRDE_SYNTAX, NULL, "$((2+))", 0, 0, { NULL, }, IFS },

     { WRDE_SYNTAX, NULL, "`", 0, 0, { NULL, }, IFS },

     { WRDE_SYNTAX, NULL, "$((010+4+))", 0, 0, { NULL }, IFS },

+    /* Test for CVE-2014-7817. We test 3 combinations of command

+       substitution inside an arithmetic expression to make sure that

+       no commands are executed and error is returned.  */

+    { WRDE_CMDSUB, NULL, "$((`echo 1`))", WRDE_NOCMD, 0, { NULL, }, IFS },

+    { WRDE_CMDSUB, NULL, "$((1+`echo 1`))", WRDE_NOCMD, 0, { NULL, }, IFS },

+    { WRDE_CMDSUB, NULL, "$((1+$((`echo 1`))))", WRDE_NOCMD, 0, { NULL, }, IFS },

     { -1, NULL, NULL, 0, 0, { NULL, }, IFS },

   };

@@ -258,6 +283,15 @@ main (int argc, char *argv[])

 	  return -1;

     }

+  /* If we are not allowed to do command substitution, we install

+     fork handlers to verify that no forks happened.  No forks should

+     happen at all if command substitution is disabled.  */

+  if (__app_register_atfork (register_fork, NULL, NULL) != 0)

+    {

+      printf ("Failed to register fork handler.\n");

+      return -1;

+    }

+

   for (test = 0; test_case[test].retval != -1; test++)

     if (testit (&test_case[test]))

       ++fail;

@@ -367,6 +401,9 @@ testit (struct test_case_struct *tc)

   printf ("Test %d (%s): ", ++tests, tc->words);

+  if (tc->flags & WRDE_NOCMD)

+    registered_forks = 0;

+

   if (tc->flags & WRDE_APPEND)

     {

       /* initial wordexp() call, to be appended to */

@@ -378,6 +415,13 @@ testit (struct test_case_struct *tc)

     }

   retval = wordexp (tc->words, &we, tc->flags);

+  if ((tc->flags & WRDE_NOCMD)

+      && (registered_forks > 0))

+    {

+	  printf ("FAILED fork called for WRDE_NOCMD\n");

+	  return 1;

+    }

+

   if (tc->flags & WRDE_DOOFFS)

       start_offs = sav_we.we_offs;

diff --git glibc-2.17-c758a686/posix/wordexp.c glibc-2.17-c758a686/posix/wordexp.c

index b6b65dd..26f3a26 100644

--- glibc-2.17-c758a686/posix/wordexp.c

+++ glibc-2.17-c758a686/posix/wordexp.c

@@ -893,6 +893,10 @@ exec_comm (char *comm, char **word, size_t *word_length, size_t *max_length,

   pid_t pid;

   int noexec = 0;

+  /* Do nothing if command substitution should not succeed.  */

+  if (flags & WRDE_NOCMD)

+    return WRDE_CMDSUB;

+

   /* Don't fork() unless necessary */

   if (!comm || !*comm)

     return 0;

@@ -2082,9 +2086,6 @@ parse_dollars (char **word, size_t *word_length, size_t *max_length,

 	    }

 	}

-      if (flags & WRDE_NOCMD)

-	return WRDE_CMDSUB;

-

       (*offset) += 2;

       return parse_comm (word, word_length, max_length, words, offset, flags,

 			 quoted? NULL : pwordexp, ifs, ifs_white);

@@ -2196,9 +2197,6 @@ parse_dquote (char **word, size_t *word_length, size_t *max_length,

 	  break;

 	case '`':

-	  if (flags & WRDE_NOCMD)

-	    return WRDE_CMDSUB;

-

 	  ++(*offset);

 	  error = parse_backtick (word, word_length, max_length, words,

 				  offset, flags, NULL, NULL, NULL);

@@ -2357,12 +2355,6 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)

 	break;

       case '`':

-	if (flags & WRDE_NOCMD)

-	  {

-	    error = WRDE_CMDSUB;

-	    goto do_error;

-	  }

-

 	++words_offset;

 	error = parse_backtick (&word, &word_length, &max_length, words,

 				&words_offset, flags, pwordexp, ifs,