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authorCarlos O'Donell <carlos@redhat.com>2014-11-19 11:44:12 -0500
committerCarlos O'Donell <carlos@redhat.com>2014-11-19 15:29:48 -0500
commit33ceaf6187b31ea15284ac65131749e1cb68d2ae (patch)
treea53160ae8adbc1a1840c2edd2b26d83c940ea2a3
parente42643491c47dcd1c226b4f00f716023e9bcc5ca (diff)
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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)
-rw-r--r--ChangeLog22
-rw-r--r--NEWS9
-rw-r--r--posix/wordexp-test.c44
-rw-r--r--posix/wordexp.c16
4 files changed, 78 insertions, 13 deletions
diff --git a/ChangeLog b/ChangeLog
index 31139c1743a..f9f3407f88b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,25 @@
+2014-11-19 Carlos O'Donell <carlos@redhat.com>
+ Florian Weimer <fweimer@redhat.com>
+ Joseph Myers <joseph@codesourcery.com>
+ Adam Conrad <adconrad@0c3.net>
+ Andreas Schwab <schwab@suse.de>
+ Brooks <bmoses@google.com>
+
+ [BZ #17625]
+ * wordexp-test.c (__dso_handle): Add prototype.
+ (__register_atfork): Likewise.
+ (__app_register_atfork): New function.
+ (registered_forks): New global.
+ (register_fork): New function.
+ (test_case): Add 3 new tests for WRDE_CMDSUB.
+ (main): Call __app_register_atfork.
+ (testit): If WRDE_NOCMD set registered_forks to zero, run test, and if
+ fork count is non-zero fail the test.
+ * posix/wordexp.c (exec_comm): Return WRDE_CMDSUB if WRDE_NOCMD flag
+ is set.
+ (parse_dollars): Remove check for WRDE_NOCMD.
+ (parse_dquote): Likewise.
+
2014-11-10 Renlin Li <Renlin.Li@arm.com>
[BZ #17555]
diff --git a/NEWS b/NEWS
index 1df7f5e600c..3de92cdd814 100644
--- a/NEWS
+++ b/NEWS
@@ -9,7 +9,14 @@ Version 2.20.1
* The following bugs are resolved with this release:
- 17266, 17370, 17371, 17460, 17485, 17555.
+ 17266, 17370, 17371, 17460, 17485, 17555, 17625.
+
+* CVE-2104-7817 The wordexp function could ignore the WRDE_NOCMD flag
+ under certain input conditions resulting in the execution of a shell for
+ command substitution when the applicaiton did not request it. The
+ implementation now checks WRDE_NOCMD immediately before executing the
+ shell and returns the error WRDE_CMDSUB as expected.
+
Version 2.20
diff --git a/posix/wordexp-test.c b/posix/wordexp-test.c
index 4957006da74..bdd65e439fe 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 b6b65dd993e..26f3a2653fe 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,