eglibc: CVE-2014-7817 wordexp fails to honour WRDE_NOCMD

Command execution in wordexp() with WRDE_NOCMD specified

Changes in the NEWS and ChangeLog files from the original upstream
commit have been ignored

Reference
https://sourceware.org/ml/libc-alpha/2014-11/msg00519.html

Signed-off-by: Sona Sarmadi <sona.sarmadi@enea.com>

2 files changed, 165 insertions, 0 deletions

diff --git a/meta/recipes-core/eglibc/eglibc-2.19/CVE-2014-7817-wordexp-fails-to-honour-WRDE_NOCMD.patch b/meta/recipes-core/eglibc/eglibc-2.19/CVE-2014-7817-wordexp-fails-to-honour-WRDE_NOCMD.patch
new file mode 100644
index 0000000000..6dc6b9ef16
--- /dev/null
+++ b/meta/recipes-core/eglibc/eglibc-2.19/CVE-2014-7817-wordexp-fails-to-honour-WRDE_NOCMD.patch
@@ -0,0 +1,164 @@
+From a39208bd7fb76c1b01c127b4c61f9bfd915bfe7c Mon Sep 17 00:00:00 2001
+From: Carlos O'Donell <carlos@redhat.com>
+Date: Wed, 19 Nov 2014 11:44:12 -0500
+Subject: [PATCH] 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.
+---
+ posix/wordexp-test.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
+ posix/wordexp.c      | 16 ++++------------
+
+Index: git/posix/wordexp-test.c
+===================================================================
+--- git.orig/posix/wordexp-test.c
++++ git/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;
+ 
+Index: git/posix/wordexp.c
+===================================================================
+--- git.orig/posix/wordexp.c
++++ git/posix/wordexp.c
+@@ -893,6 +893,10 @@ exec_comm (char *comm, char **word, size
+   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
+            }
+        }
+ 
+-      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_
+          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 *p
+        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,
diff --git a/meta/recipes-core/eglibc/eglibc_2.19.bb b/meta/recipes-core/eglibc/eglibc_2.19.bb
index b9e43a1b0c..ba79f27d61 100644
--- a/meta/recipes-core/eglibc/eglibc_2.19.bb
+++ b/meta/recipes-core/eglibc/eglibc_2.19.bb
@@ -26,6 +26,7 @@ SRC_URI = "http://downloads.yoctoproject.org/releases/eglibc/eglibc-${PV}-svnr25
            file://fix-tibetian-locales.patch \
            file://ppce6500-32b_slow_ieee754_sqrt.patch \
            file://CVE-2014-5119.patch \
+           file://CVE-2014-7817-wordexp-fails-to-honour-WRDE_NOCMD.patch \
           "
 SRC_URI[md5sum] = "197836c2ba42fb146e971222647198dd"
 SRC_URI[sha256sum] = "baaa030531fc308f7820c46acdf8e1b2f8e3c1f40bcd28b6e440d1c95d170d4c"