174 lines
6.0 KiB
Diff
174 lines
6.0 KiB
Diff
|
Patch from https://bugzilla.redhat.com/show_bug.cgi?id=1157689
|
||
|
|
||
|
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/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..d6a158f 100644
|
||
|
--- a/posix/wordexp.c
|
||
|
+++ b/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);
|