src/patches/glibc/glibc-rh1170121.patch

   1 #
   2 # commit a39208bd7fb76c1b01c127b4c61f9bfd915bfe7c
   3 # Author: Carlos O'Donell <carlos@redhat.com>
   4 # Date:   Wed Nov 19 11:44:12 2014 -0500
   5 #
   6 #     CVE-2014-7817: wordexp fails to honour WRDE_NOCMD.
   7 #
   8 #     The function wordexp() fails to properly handle the WRDE_NOCMD
   9 #     flag when processing arithmetic inputs in the form of "$((... ``))"
  10 #     where "..." can be anything valid. The backticks in the arithmetic
  11 #     epxression are evaluated by in a shell even if WRDE_NOCMD forbade
  12 #     command substitution. This allows an attacker to attempt to pass
  13 #     dangerous commands via constructs of the above form, and bypass
  14 #     the WRDE_NOCMD flag. This patch fixes this by checking for WRDE_NOCMD
  15 #     in exec_comm(), the only place that can execute a shell. All other
  16 #     checks for WRDE_NOCMD are superfluous and removed.
  17 #
  18 #     We expand the testsuite and add 3 new regression tests of roughly
  19 #     the same form but with a couple of nested levels.
  20 #
  21 #     On top of the 3 new tests we add fork validation to the WRDE_NOCMD
  22 #     testing. If any forks are detected during the execution of a wordexp()
  23 #     call with WRDE_NOCMD, the test is marked as failed. This is slightly
  24 #     heuristic since vfork might be used in the future, but it provides a
  25 #     higher level of assurance that no shells were executed as part of
  26 #     command substitution with WRDE_NOCMD in effect. In addition it doesn't
  27 #     require libpthread or libdl, instead we use the public implementation
  28 #     namespace function __register_atfork (already part of the public ABI
  29 #     for libpthread).
  30 #
  31 #     Tested on x86_64 with no regressions.
  32 #
  33 diff --git a/posix/wordexp-test.c b/posix/wordexp-test.c
  34 index 4957006..bdd65e4 100644
  35 --- a/posix/wordexp-test.c
  36 +++ b/posix/wordexp-test.c
  37 @@ -27,6 +27,25 @@
  38
  39  #define IFS " \n\t"
  40
  41 +extern void *__dso_handle __attribute__ ((__weak__, __visibility__ ("hidden")));
  42 +extern int __register_atfork (void (*) (void), void (*) (void), void (*) (void), void *);
  43 +
  44 +static int __app_register_atfork (void (*prepare) (void), void (*parent) (void), void (*child) (void))
  45 +{
  46 +  return __register_atfork (prepare, parent, child,
  47 +                           &__dso_handle == NULL ? NULL : __dso_handle);
  48 +}
  49 +
  50 +/* Number of forks seen.  */
  51 +static int registered_forks;
  52 +
  53 +/* For each fork increment the fork count.  */
  54 +static void
  55 +register_fork (void)
  56 +{
  57 +  registered_forks++;
  58 +}
  59 +
  60  struct test_case_struct
  61  {
  62    int retval;
  63 @@ -206,6 +225,12 @@ struct test_case_struct
  64      { WRDE_SYNTAX, NULL, "$((2+))", 0, 0, { NULL, }, IFS },
  65      { WRDE_SYNTAX, NULL, "`", 0, 0, { NULL, }, IFS },
  66      { WRDE_SYNTAX, NULL, "$((010+4+))", 0, 0, { NULL }, IFS },
  67 +    /* Test for CVE-2014-7817. We test 3 combinations of command
  68 +       substitution inside an arithmetic expression to make sure that
  69 +       no commands are executed and error is returned.  */
  70 +    { WRDE_CMDSUB, NULL, "$((`echo 1`))", WRDE_NOCMD, 0, { NULL, }, IFS },
  71 +    { WRDE_CMDSUB, NULL, "$((1+`echo 1`))", WRDE_NOCMD, 0, { NULL, }, IFS },
  72 +    { WRDE_CMDSUB, NULL, "$((1+$((`echo 1`))))", WRDE_NOCMD, 0, { NULL, }, IFS },
  73
  74      { -1, NULL, NULL, 0, 0, { NULL, }, IFS },
  75    };
  76 @@ -258,6 +283,15 @@ main (int argc, char *argv[])
  77           return -1;
  78      }
  79
  80 +  /* If we are not allowed to do command substitution, we install
  81 +     fork handlers to verify that no forks happened.  No forks should
  82 +     happen at all if command substitution is disabled.  */
  83 +  if (__app_register_atfork (register_fork, NULL, NULL) != 0)
  84 +    {
  85 +      printf ("Failed to register fork handler.\n");
  86 +      return -1;
  87 +    }
  88 +
  89    for (test = 0; test_case[test].retval != -1; test++)
  90      if (testit (&test_case[test]))
  91        ++fail;
  92 @@ -367,6 +401,9 @@ testit (struct test_case_struct *tc)
  93
  94    printf ("Test %d (%s): ", ++tests, tc->words);
  95
  96 +  if (tc->flags & WRDE_NOCMD)
  97 +    registered_forks = 0;
  98 +
  99    if (tc->flags & WRDE_APPEND)
 100      {
 101        /* initial wordexp() call, to be appended to */
 102 @@ -378,6 +415,13 @@ testit (struct test_case_struct *tc)
 103      }
 104    retval = wordexp (tc->words, &we, tc->flags);
 105
 106 +  if ((tc->flags & WRDE_NOCMD)
 107 +      && (registered_forks > 0))
 108 +    {
 109 +         printf ("FAILED fork called for WRDE_NOCMD\n");
 110 +         return 1;
 111 +    }
 112 +
 113    if (tc->flags & WRDE_DOOFFS)
 114        start_offs = sav_we.we_offs;
 115
 116 diff --git a/posix/wordexp.c b/posix/wordexp.c
 117 index b6b65dd..26f3a26 100644
 118 --- a/posix/wordexp.c
 119 +++ b/posix/wordexp.c
 120 @@ -893,6 +893,10 @@ exec_comm (char *comm, char **word, size_t *word_length, size_t *max_length,
 121    pid_t pid;
 122    int noexec = 0;
 123
 124 +  /* Do nothing if command substitution should not succeed.  */
 125 +  if (flags & WRDE_NOCMD)
 126 +    return WRDE_CMDSUB;
 127 +
 128    /* Don't fork() unless necessary */
 129    if (!comm || !*comm)
 130      return 0;
 131 @@ -2082,9 +2086,6 @@ parse_dollars (char **word, size_t *word_length, size_t *max_length,
 132             }
 133         }
 134
 135 -      if (flags & WRDE_NOCMD)
 136 -       return WRDE_CMDSUB;
 137 -
 138        (*offset) += 2;
 139        return parse_comm (word, word_length, max_length, words, offset, flags,
 140                          quoted? NULL : pwordexp, ifs, ifs_white);
 141 @@ -2196,9 +2197,6 @@ parse_dquote (char **word, size_t *word_length, size_t *max_length,
 142           break;
 143
 144         case '`':
 145 -         if (flags & WRDE_NOCMD)
 146 -           return WRDE_CMDSUB;
 147 -
 148           ++(*offset);
 149           error = parse_backtick (word, word_length, max_length, words,
 150                                   offset, flags, NULL, NULL, NULL);
 151 @@ -2357,12 +2355,6 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)
 152         break;
 153
 154        case '`':
 155 -       if (flags & WRDE_NOCMD)
 156 -         {
 157 -           error = WRDE_CMDSUB;
 158 -           goto do_error;
 159 -         }
 160 -
 161         ++words_offset;
 162         error = parse_backtick (&word, &word_length, &max_length, words,
 163                                 &words_offset, flags, pwordexp, ifs,