--- /dev/null
+From https://bugzilla.redhat.com/show_bug.cgi?id=1157689
+Modified for eglibc.
+
+Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
+
+WARNING !!! WARNING !!! WARNING !!! WARNING !!! WARNING !!! WARNING !!!
+EMBARGOED !!! EMBARGOED !!! EMARGOED !!! EMBARGOED !!! EMBARGOED !!!
+SECURITY !!! SECURITY !!! SECURITY !!! SECURITY !!! SECURITY !!!
+
+CVE-2014-7817:
+
+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 parse_arith(). The patch also hardens parse_backticks() and
+parse_comm() to check for WRDE_NOCMD flag and return an error instead
+of ever running a shell.
+
+We expand the testsuite and add 3 new regression tests of roughtly
+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, 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.
+
+2014-10-27 Carlos O'Donell <carlos@redhat.com>
+
+ * 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 (parse_arith): Return WRDE_NOCMD if WRDE_NOCMD flag
+ is set and parsing '`'.
+ (parse_comm): Return WRDE_NOCMD if WRDE_NOCMD flag is set.
+ (parse_backtick): Return WRDE_NOCMD if WRDE_NOCMD flag is set and
+ parsing '`'.
+
+diff --git a/posix/wordexp-test.c b/posix/wordexp-test.c
+index 4957006..5ce2a1b 100644
+--- a/libc/posix/wordexp-test.c
++++ b/libc/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..d6a158f 100644
+--- a/libc/posix/wordexp.c
++++ b/libc/posix/wordexp.c
+@@ -693,6 +693,12 @@ parse_arith (char **word, size_t *word_length, size_t *max_length,
+ break;
+
+ case '`':
++ if (flags & WRDE_NOCMD)
++ {
++ free (expr);
++ return WRDE_NOCMD;
++ }
++
+ (*offset)++;
+ error = parse_backtick (&expr, &expr_length, &expr_maxlen,
+ words, offset, flags, NULL, NULL, NULL);
+@@ -1144,6 +1150,10 @@ parse_comm (char **word, size_t *word_length, size_t *max_length,
+ size_t comm_maxlen;
+ char *comm = w_newword (&comm_length, &comm_maxlen);
+
++ /* Do nothing if command substitution should not succeed. */
++ if (flags & WRDE_NOCMD)
++ return WRDE_CMDSUB;
++
+ for (; words[*offset]; ++(*offset))
+ {
+ switch (words[*offset])
+@@ -2121,6 +2131,9 @@ parse_backtick (char **word, size_t *word_length, size_t *max_length,
+ switch (words[*offset])
+ {
+ case '`':
++ if (flags & WRDE_NOCMD)
++ return WRDE_NOCMD;
++
+ /* Go -- give the script to the shell */
+ error = exec_comm (comm, word, word_length, max_length, flags,
+ pwordexp, ifs, ifs_white);
Code Review / packages / trusty / cirros-testvm.git / blobdiff