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1 | # |
2 | # commit a39208bd7fb76c1b01c127b4c61f9bfd915bfe7c | |
3 | # Author: Carlos O'Donell <carlos@redhat.com> | |
4 | # Date: Wed Nov 19 11:44:12 2014 -0500 | |
5 | # | |
6 | # CVE-2014-7817: wordexp fails to honour WRDE_NOCMD. | |
7 | # | |
8 | # The function wordexp() fails to properly handle the WRDE_NOCMD | |
9 | # flag when processing arithmetic inputs in the form of "$((... ``))" | |
10 | # where "..." can be anything valid. The backticks in the arithmetic | |
11 | # epxression are evaluated by in a shell even if WRDE_NOCMD forbade | |
12 | # command substitution. This allows an attacker to attempt to pass | |
13 | # dangerous commands via constructs of the above form, and bypass | |
14 | # the WRDE_NOCMD flag. This patch fixes this by checking for WRDE_NOCMD | |
15 | # in exec_comm(), the only place that can execute a shell. All other | |
16 | # checks for WRDE_NOCMD are superfluous and removed. | |
17 | # | |
18 | # We expand the testsuite and add 3 new regression tests of roughly | |
19 | # the same form but with a couple of nested levels. | |
20 | # | |
21 | # On top of the 3 new tests we add fork validation to the WRDE_NOCMD | |
22 | # testing. If any forks are detected during the execution of a wordexp() | |
23 | # call with WRDE_NOCMD, the test is marked as failed. This is slightly | |
24 | # heuristic since vfork might be used in the future, but it provides a | |
25 | # higher level of assurance that no shells were executed as part of | |
26 | # command substitution with WRDE_NOCMD in effect. In addition it doesn't | |
27 | # require libpthread or libdl, instead we use the public implementation | |
28 | # namespace function __register_atfork (already part of the public ABI | |
29 | # for libpthread). | |
30 | # | |
31 | # Tested on x86_64 with no regressions. | |
32 | # | |
33 | diff --git a/posix/wordexp-test.c b/posix/wordexp-test.c | |
34 | index 4957006..bdd65e4 100644 | |
35 | --- a/posix/wordexp-test.c | |
36 | +++ b/posix/wordexp-test.c | |
37 | @@ -27,6 +27,25 @@ | |
38 | ||
39 | #define IFS " \n\t" | |
40 | ||
41 | +extern void *__dso_handle __attribute__ ((__weak__, __visibility__ ("hidden"))); | |
42 | +extern int __register_atfork (void (*) (void), void (*) (void), void (*) (void), void *); | |
43 | + | |
44 | +static int __app_register_atfork (void (*prepare) (void), void (*parent) (void), void (*child) (void)) | |
45 | +{ | |
46 | + return __register_atfork (prepare, parent, child, | |
47 | + &__dso_handle == NULL ? NULL : __dso_handle); | |
48 | +} | |
49 | + | |
50 | +/* Number of forks seen. */ | |
51 | +static int registered_forks; | |
52 | + | |
53 | +/* For each fork increment the fork count. */ | |
54 | +static void | |
55 | +register_fork (void) | |
56 | +{ | |
57 | + registered_forks++; | |
58 | +} | |
59 | + | |
60 | struct test_case_struct | |
61 | { | |
62 | int retval; | |
63 | @@ -206,6 +225,12 @@ struct test_case_struct | |
64 | { WRDE_SYNTAX, NULL, "$((2+))", 0, 0, { NULL, }, IFS }, | |
65 | { WRDE_SYNTAX, NULL, "`", 0, 0, { NULL, }, IFS }, | |
66 | { WRDE_SYNTAX, NULL, "$((010+4+))", 0, 0, { NULL }, IFS }, | |
67 | + /* Test for CVE-2014-7817. We test 3 combinations of command | |
68 | + substitution inside an arithmetic expression to make sure that | |
69 | + no commands are executed and error is returned. */ | |
70 | + { WRDE_CMDSUB, NULL, "$((`echo 1`))", WRDE_NOCMD, 0, { NULL, }, IFS }, | |
71 | + { WRDE_CMDSUB, NULL, "$((1+`echo 1`))", WRDE_NOCMD, 0, { NULL, }, IFS }, | |
72 | + { WRDE_CMDSUB, NULL, "$((1+$((`echo 1`))))", WRDE_NOCMD, 0, { NULL, }, IFS }, | |
73 | ||
74 | { -1, NULL, NULL, 0, 0, { NULL, }, IFS }, | |
75 | }; | |
76 | @@ -258,6 +283,15 @@ main (int argc, char *argv[]) | |
77 | return -1; | |
78 | } | |
79 | ||
80 | + /* If we are not allowed to do command substitution, we install | |
81 | + fork handlers to verify that no forks happened. No forks should | |
82 | + happen at all if command substitution is disabled. */ | |
83 | + if (__app_register_atfork (register_fork, NULL, NULL) != 0) | |
84 | + { | |
85 | + printf ("Failed to register fork handler.\n"); | |
86 | + return -1; | |
87 | + } | |
88 | + | |
89 | for (test = 0; test_case[test].retval != -1; test++) | |
90 | if (testit (&test_case[test])) | |
91 | ++fail; | |
92 | @@ -367,6 +401,9 @@ testit (struct test_case_struct *tc) | |
93 | ||
94 | printf ("Test %d (%s): ", ++tests, tc->words); | |
95 | ||
96 | + if (tc->flags & WRDE_NOCMD) | |
97 | + registered_forks = 0; | |
98 | + | |
99 | if (tc->flags & WRDE_APPEND) | |
100 | { | |
101 | /* initial wordexp() call, to be appended to */ | |
102 | @@ -378,6 +415,13 @@ testit (struct test_case_struct *tc) | |
103 | } | |
104 | retval = wordexp (tc->words, &we, tc->flags); | |
105 | ||
106 | + if ((tc->flags & WRDE_NOCMD) | |
107 | + && (registered_forks > 0)) | |
108 | + { | |
109 | + printf ("FAILED fork called for WRDE_NOCMD\n"); | |
110 | + return 1; | |
111 | + } | |
112 | + | |
113 | if (tc->flags & WRDE_DOOFFS) | |
114 | start_offs = sav_we.we_offs; | |
115 | ||
116 | diff --git a/posix/wordexp.c b/posix/wordexp.c | |
117 | index b6b65dd..26f3a26 100644 | |
118 | --- a/posix/wordexp.c | |
119 | +++ b/posix/wordexp.c | |
120 | @@ -893,6 +893,10 @@ exec_comm (char *comm, char **word, size_t *word_length, size_t *max_length, | |
121 | pid_t pid; | |
122 | int noexec = 0; | |
123 | ||
124 | + /* Do nothing if command substitution should not succeed. */ | |
125 | + if (flags & WRDE_NOCMD) | |
126 | + return WRDE_CMDSUB; | |
127 | + | |
128 | /* Don't fork() unless necessary */ | |
129 | if (!comm || !*comm) | |
130 | return 0; | |
131 | @@ -2082,9 +2086,6 @@ parse_dollars (char **word, size_t *word_length, size_t *max_length, | |
132 | } | |
133 | } | |
134 | ||
135 | - if (flags & WRDE_NOCMD) | |
136 | - return WRDE_CMDSUB; | |
137 | - | |
138 | (*offset) += 2; | |
139 | return parse_comm (word, word_length, max_length, words, offset, flags, | |
140 | quoted? NULL : pwordexp, ifs, ifs_white); | |
141 | @@ -2196,9 +2197,6 @@ parse_dquote (char **word, size_t *word_length, size_t *max_length, | |
142 | break; | |
143 | ||
144 | case '`': | |
145 | - if (flags & WRDE_NOCMD) | |
146 | - return WRDE_CMDSUB; | |
147 | - | |
148 | ++(*offset); | |
149 | error = parse_backtick (word, word_length, max_length, words, | |
150 | offset, flags, NULL, NULL, NULL); | |
151 | @@ -2357,12 +2355,6 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags) | |
152 | break; | |
153 | ||
154 | case '`': | |
155 | - if (flags & WRDE_NOCMD) | |
156 | - { | |
157 | - error = WRDE_CMDSUB; | |
158 | - goto do_error; | |
159 | - } | |
160 | - | |
161 | ++words_offset; | |
162 | error = parse_backtick (&word, &word_length, &max_length, words, | |
163 | &words_offset, flags, pwordexp, ifs, |