172 lines
5.8 KiB
Diff
172 lines
5.8 KiB
Diff
Fix CVE-2014-7817: wordexp fails to honour WRDE_NOCMD.
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Note: Here the ChangeLog and NEWS updates are removed from Carlos's
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patch, since they depend on other earlier commits.
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From: Carlos O'Donell <carlos@redhat.com>
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Date: Wed, 19 Nov 2014 16:44:12 +0000 (-0500)
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Subject: CVE-2014-7817: wordexp fails to honour WRDE_NOCMD.
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X-Git-Url: https://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff_plain;h=33ceaf6187b31ea15284ac65131749e1cb68d2ae
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CVE-2014-7817: wordexp fails to honour WRDE_NOCMD.
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The function wordexp() fails to properly handle the WRDE_NOCMD
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flag when processing arithmetic inputs in the form of "$((... ``))"
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where "..." can be anything valid. The backticks in the arithmetic
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epxression are evaluated by in a shell even if WRDE_NOCMD forbade
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command substitution. This allows an attacker to attempt to pass
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dangerous commands via constructs of the above form, and bypass
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the WRDE_NOCMD flag. This patch fixes this by checking for WRDE_NOCMD
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in exec_comm(), the only place that can execute a shell. All other
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checks for WRDE_NOCMD are superfluous and removed.
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We expand the testsuite and add 3 new regression tests of roughly
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the same form but with a couple of nested levels.
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On top of the 3 new tests we add fork validation to the WRDE_NOCMD
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testing. If any forks are detected during the execution of a wordexp()
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call with WRDE_NOCMD, the test is marked as failed. This is slightly
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heuristic since vfork might be used in the future, but it provides a
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higher level of assurance that no shells were executed as part of
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command substitution with WRDE_NOCMD in effect. In addition it doesn't
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require libpthread or libdl, instead we use the public implementation
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namespace function __register_atfork (already part of the public ABI
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for libpthread).
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Tested on x86_64 with no regressions.
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(cherry picked from commit a39208bd7fb76c1b01c127b4c61f9bfd915bfe7c)
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---
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diff --git a/posix/wordexp-test.c b/posix/wordexp-test.c
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index 4957006..bdd65e4 100644
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--- a/posix/wordexp-test.c
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+++ b/posix/wordexp-test.c
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@@ -27,6 +27,25 @@
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#define IFS " \n\t"
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+extern void *__dso_handle __attribute__ ((__weak__, __visibility__ ("hidden")));
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+extern int __register_atfork (void (*) (void), void (*) (void), void (*) (void), void *);
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+
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+static int __app_register_atfork (void (*prepare) (void), void (*parent) (void), void (*child) (void))
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+{
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+ return __register_atfork (prepare, parent, child,
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+ &__dso_handle == NULL ? NULL : __dso_handle);
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+}
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+
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+/* Number of forks seen. */
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+static int registered_forks;
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+
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+/* For each fork increment the fork count. */
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+static void
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+register_fork (void)
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+{
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+ registered_forks++;
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+}
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+
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struct test_case_struct
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{
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int retval;
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@@ -206,6 +225,12 @@ struct test_case_struct
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{ WRDE_SYNTAX, NULL, "$((2+))", 0, 0, { NULL, }, IFS },
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{ WRDE_SYNTAX, NULL, "`", 0, 0, { NULL, }, IFS },
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{ WRDE_SYNTAX, NULL, "$((010+4+))", 0, 0, { NULL }, IFS },
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+ /* Test for CVE-2014-7817. We test 3 combinations of command
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+ substitution inside an arithmetic expression to make sure that
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+ no commands are executed and error is returned. */
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+ { WRDE_CMDSUB, NULL, "$((`echo 1`))", WRDE_NOCMD, 0, { NULL, }, IFS },
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+ { WRDE_CMDSUB, NULL, "$((1+`echo 1`))", WRDE_NOCMD, 0, { NULL, }, IFS },
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+ { WRDE_CMDSUB, NULL, "$((1+$((`echo 1`))))", WRDE_NOCMD, 0, { NULL, }, IFS },
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{ -1, NULL, NULL, 0, 0, { NULL, }, IFS },
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};
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@@ -258,6 +283,15 @@ main (int argc, char *argv[])
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return -1;
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}
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+ /* If we are not allowed to do command substitution, we install
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+ fork handlers to verify that no forks happened. No forks should
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+ happen at all if command substitution is disabled. */
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+ if (__app_register_atfork (register_fork, NULL, NULL) != 0)
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+ {
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+ printf ("Failed to register fork handler.\n");
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+ return -1;
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+ }
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+
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for (test = 0; test_case[test].retval != -1; test++)
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if (testit (&test_case[test]))
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++fail;
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@@ -367,6 +401,9 @@ testit (struct test_case_struct *tc)
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printf ("Test %d (%s): ", ++tests, tc->words);
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+ if (tc->flags & WRDE_NOCMD)
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+ registered_forks = 0;
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+
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if (tc->flags & WRDE_APPEND)
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{
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/* initial wordexp() call, to be appended to */
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@@ -378,6 +415,13 @@ testit (struct test_case_struct *tc)
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}
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retval = wordexp (tc->words, &we, tc->flags);
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+ if ((tc->flags & WRDE_NOCMD)
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+ && (registered_forks > 0))
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+ {
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+ printf ("FAILED fork called for WRDE_NOCMD\n");
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+ return 1;
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+ }
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+
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if (tc->flags & WRDE_DOOFFS)
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start_offs = sav_we.we_offs;
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diff --git a/posix/wordexp.c b/posix/wordexp.c
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index b6b65dd..26f3a26 100644
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--- a/posix/wordexp.c
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+++ b/posix/wordexp.c
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@@ -893,6 +893,10 @@ exec_comm (char *comm, char **word, size_t *word_length, size_t *max_length,
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pid_t pid;
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int noexec = 0;
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+ /* Do nothing if command substitution should not succeed. */
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+ if (flags & WRDE_NOCMD)
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+ return WRDE_CMDSUB;
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+
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/* Don't fork() unless necessary */
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if (!comm || !*comm)
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return 0;
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@@ -2082,9 +2086,6 @@ parse_dollars (char **word, size_t *word_length, size_t *max_length,
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}
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}
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- if (flags & WRDE_NOCMD)
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- return WRDE_CMDSUB;
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-
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(*offset) += 2;
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return parse_comm (word, word_length, max_length, words, offset, flags,
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quoted? NULL : pwordexp, ifs, ifs_white);
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@@ -2196,9 +2197,6 @@ parse_dquote (char **word, size_t *word_length, size_t *max_length,
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break;
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case '`':
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- if (flags & WRDE_NOCMD)
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- return WRDE_CMDSUB;
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-
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++(*offset);
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error = parse_backtick (word, word_length, max_length, words,
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offset, flags, NULL, NULL, NULL);
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@@ -2357,12 +2355,6 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags)
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break;
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case '`':
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- if (flags & WRDE_NOCMD)
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- {
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- error = WRDE_CMDSUB;
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- goto do_error;
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- }
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-
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++words_offset;
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error = parse_backtick (&word, &word_length, &max_length, words,
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&words_offset, flags, pwordexp, ifs,
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