| 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); |