[glibc/f21] CVE-2014-7817: wordexp fails to honour WRDE_NOCMD (#1167569).
Siddhesh Poyarekar
siddhesh at fedoraproject.org
Fri Feb 27 11:10:40 UTC 2015
commit 07eee66da3912fc8333546ec04e8c1df4a5cb1b6
Author: Siddhesh Poyarekar <siddhesh at redhat.com>
Date: Fri Feb 27 15:46:25 2015 +0530
CVE-2014-7817: wordexp fails to honour WRDE_NOCMD (#1167569).
glibc-rh1167569.patch | 164 ++++++++++++++++++++++++++++++++++++++++++++++++++
glibc.spec | 7 ++-
2 files changed, 170 insertions(+), 1 deletion(-)
---
diff --git a/glibc-rh1167569.patch b/glibc-rh1167569.patch
new file mode 100644
index 0000000..bd9ba56
--- /dev/null
+++ b/glibc-rh1167569.patch
@@ -0,0 +1,164 @@
+commit 33ceaf6187b31ea15284ac65131749e1cb68d2ae
+Author: Carlos O'Donell <carlos at 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.
+
+ (cherry picked from commit a39208bd7fb76c1b01c127b4c61f9bfd915bfe7c)
+
+diff --git a/posix/wordexp-test.c b/posix/wordexp-test.c
+index 4957006..bdd65e4 100644
+--- a/posix/wordexp-test.c
++++ b/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 a/posix/wordexp.c b/posix/wordexp.c
+index b6b65dd..26f3a26 100644
+--- a/posix/wordexp.c
++++ b/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,
diff --git a/glibc.spec b/glibc.spec
index 25b62a2..9a32b31 100644
--- a/glibc.spec
+++ b/glibc.spec
@@ -1,6 +1,6 @@
%define glibcsrcdir glibc-2.20
%define glibcversion 2.20
-%define glibcrelease 7%{?dist}
+%define glibcrelease 8%{?dist}
# Pre-release tarballs are pulled in from git using a command that is
# effectively:
#
@@ -207,6 +207,7 @@ Patch0051: %{name}-disable-rwlock-elision.patch
#
##############################################################################
Patch1001: %{name}-rh1133508.patch
+Patch1002: %{name}-rh1167569.patch
##############################################################################
#
@@ -575,6 +576,7 @@ package or when debugging this package.
%patch0050 -p1
%patch1001 -p1
%patch0051 -p1
+%patch1002 -p1
##############################################################################
# %%prep - Additional prep required...
@@ -1710,6 +1712,9 @@ rm -f *.filelist*
%endif
%changelog
+* Fri Feb 27 2015 Siddhesh Poyarekar <siddhesh at redhat.com> - 2.20-8
+- wordexp fails to honour WRDE_NOCMD (CVE-2014-7817, #1167569).
+
* Tue Jan 06 2015 Siddhesh Poyarekar <siddhesh at redhat.com> - 2.20-7
- Remove LIB_LANG since we don't install locales in /usr/lib/locale anymore.
- Don't own any directories in /usr/share/locale (#1167445).
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