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3d9e9aa9 VM |
1 | From b9b6e3f01655942891bf4c66a2c5e8246cdad7e1 Mon Sep 17 00:00:00 2001 |
2 | From: Carlos O'Donell <carlos@redhat.com> | |
3 | Date: Wed, 19 Nov 2014 11:44:12 -0500 | |
4 | Subject: [PATCH 1/2] CVE-2014-7817: wordexp fails to honour WRDE_NOCMD. | |
5 | ||
6 | The function wordexp() fails to properly handle the WRDE_NOCMD | |
7 | flag when processing arithmetic inputs in the form of "$((... ``))" | |
8 | where "..." can be anything valid. The backticks in the arithmetic | |
9 | epxression are evaluated by in a shell even if WRDE_NOCMD forbade | |
10 | command substitution. This allows an attacker to attempt to pass | |
11 | dangerous commands via constructs of the above form, and bypass | |
12 | the WRDE_NOCMD flag. This patch fixes this by checking for WRDE_NOCMD | |
13 | in exec_comm(), the only place that can execute a shell. All other | |
14 | checks for WRDE_NOCMD are superfluous and removed. | |
15 | ||
16 | We expand the testsuite and add 3 new regression tests of roughly | |
17 | the same form but with a couple of nested levels. | |
18 | ||
19 | On top of the 3 new tests we add fork validation to the WRDE_NOCMD | |
20 | testing. If any forks are detected during the execution of a wordexp() | |
21 | call with WRDE_NOCMD, the test is marked as failed. This is slightly | |
22 | heuristic since vfork might be used in the future, but it provides a | |
23 | higher level of assurance that no shells were executed as part of | |
24 | command substitution with WRDE_NOCMD in effect. In addition it doesn't | |
25 | require libpthread or libdl, instead we use the public implementation | |
26 | namespace function __register_atfork (already part of the public ABI | |
27 | for libpthread). | |
28 | ||
29 | Tested on x86_64 with no regressions. | |
30 | ||
31 | Conflicts: | |
32 | ChangeLog | |
33 | NEWS | |
34 | --- | |
35 | ChangeLog | 266 +++++++++++++++++++++++++++++++++++++++++++++++++++ | |
36 | NEWS | 10 ++ | |
37 | posix/wordexp-test.c | 44 +++++++++ | |
38 | posix/wordexp.c | 16 +--- | |
39 | 4 files changed, 324 insertions(+), 12 deletions(-) | |
40 | ||
41 | diff --git a/posix/wordexp-test.c b/posix/wordexp-test.c | |
42 | index 4957006..bdd65e4 100644 | |
43 | --- a/posix/wordexp-test.c | |
44 | +++ b/posix/wordexp-test.c | |
45 | @@ -27,6 +27,25 @@ | |
46 | ||
47 | #define IFS " \n\t" | |
48 | ||
49 | +extern void *__dso_handle __attribute__ ((__weak__, __visibility__ ("hidden"))); | |
50 | +extern int __register_atfork (void (*) (void), void (*) (void), void (*) (void), void *); | |
51 | + | |
52 | +static int __app_register_atfork (void (*prepare) (void), void (*parent) (void), void (*child) (void)) | |
53 | +{ | |
54 | + return __register_atfork (prepare, parent, child, | |
55 | + &__dso_handle == NULL ? NULL : __dso_handle); | |
56 | +} | |
57 | + | |
58 | +/* Number of forks seen. */ | |
59 | +static int registered_forks; | |
60 | + | |
61 | +/* For each fork increment the fork count. */ | |
62 | +static void | |
63 | +register_fork (void) | |
64 | +{ | |
65 | + registered_forks++; | |
66 | +} | |
67 | + | |
68 | struct test_case_struct | |
69 | { | |
70 | int retval; | |
71 | @@ -206,6 +225,12 @@ struct test_case_struct | |
72 | { WRDE_SYNTAX, NULL, "$((2+))", 0, 0, { NULL, }, IFS }, | |
73 | { WRDE_SYNTAX, NULL, "`", 0, 0, { NULL, }, IFS }, | |
74 | { WRDE_SYNTAX, NULL, "$((010+4+))", 0, 0, { NULL }, IFS }, | |
75 | + /* Test for CVE-2014-7817. We test 3 combinations of command | |
76 | + substitution inside an arithmetic expression to make sure that | |
77 | + no commands are executed and error is returned. */ | |
78 | + { WRDE_CMDSUB, NULL, "$((`echo 1`))", WRDE_NOCMD, 0, { NULL, }, IFS }, | |
79 | + { WRDE_CMDSUB, NULL, "$((1+`echo 1`))", WRDE_NOCMD, 0, { NULL, }, IFS }, | |
80 | + { WRDE_CMDSUB, NULL, "$((1+$((`echo 1`))))", WRDE_NOCMD, 0, { NULL, }, IFS }, | |
81 | ||
82 | { -1, NULL, NULL, 0, 0, { NULL, }, IFS }, | |
83 | }; | |
84 | @@ -258,6 +283,15 @@ main (int argc, char *argv[]) | |
85 | return -1; | |
86 | } | |
87 | ||
88 | + /* If we are not allowed to do command substitution, we install | |
89 | + fork handlers to verify that no forks happened. No forks should | |
90 | + happen at all if command substitution is disabled. */ | |
91 | + if (__app_register_atfork (register_fork, NULL, NULL) != 0) | |
92 | + { | |
93 | + printf ("Failed to register fork handler.\n"); | |
94 | + return -1; | |
95 | + } | |
96 | + | |
97 | for (test = 0; test_case[test].retval != -1; test++) | |
98 | if (testit (&test_case[test])) | |
99 | ++fail; | |
100 | @@ -367,6 +401,9 @@ testit (struct test_case_struct *tc) | |
101 | ||
102 | printf ("Test %d (%s): ", ++tests, tc->words); | |
103 | ||
104 | + if (tc->flags & WRDE_NOCMD) | |
105 | + registered_forks = 0; | |
106 | + | |
107 | if (tc->flags & WRDE_APPEND) | |
108 | { | |
109 | /* initial wordexp() call, to be appended to */ | |
110 | @@ -378,6 +415,13 @@ testit (struct test_case_struct *tc) | |
111 | } | |
112 | retval = wordexp (tc->words, &we, tc->flags); | |
113 | ||
114 | + if ((tc->flags & WRDE_NOCMD) | |
115 | + && (registered_forks > 0)) | |
116 | + { | |
117 | + printf ("FAILED fork called for WRDE_NOCMD\n"); | |
118 | + return 1; | |
119 | + } | |
120 | + | |
121 | if (tc->flags & WRDE_DOOFFS) | |
122 | start_offs = sav_we.we_offs; | |
123 | ||
124 | diff --git a/posix/wordexp.c b/posix/wordexp.c | |
125 | index 366ec18..36a1367 100644 | |
126 | --- a/posix/wordexp.c | |
127 | +++ b/posix/wordexp.c | |
128 | @@ -893,6 +893,10 @@ exec_comm (char *comm, char **word, size_t *word_length, size_t *max_length, | |
129 | pid_t pid; | |
130 | int noexec = 0; | |
131 | ||
132 | + /* Do nothing if command substitution should not succeed. */ | |
133 | + if (flags & WRDE_NOCMD) | |
134 | + return WRDE_CMDSUB; | |
135 | + | |
136 | /* Don't fork() unless necessary */ | |
137 | if (!comm || !*comm) | |
138 | return 0; | |
139 | @@ -2082,9 +2086,6 @@ parse_dollars (char **word, size_t *word_length, size_t *max_length, | |
140 | } | |
141 | } | |
142 | ||
143 | - if (flags & WRDE_NOCMD) | |
144 | - return WRDE_CMDSUB; | |
145 | - | |
146 | (*offset) += 2; | |
147 | return parse_comm (word, word_length, max_length, words, offset, flags, | |
148 | quoted? NULL : pwordexp, ifs, ifs_white); | |
149 | @@ -2196,9 +2197,6 @@ parse_dquote (char **word, size_t *word_length, size_t *max_length, | |
150 | break; | |
151 | ||
152 | case '`': | |
153 | - if (flags & WRDE_NOCMD) | |
154 | - return WRDE_CMDSUB; | |
155 | - | |
156 | ++(*offset); | |
157 | error = parse_backtick (word, word_length, max_length, words, | |
158 | offset, flags, NULL, NULL, NULL); | |
159 | @@ -2357,12 +2355,6 @@ wordexp (const char *words, wordexp_t *pwordexp, int flags) | |
160 | break; | |
161 | ||
162 | case '`': | |
163 | - if (flags & WRDE_NOCMD) | |
164 | - { | |
165 | - error = WRDE_CMDSUB; | |
166 | - goto do_error; | |
167 | - } | |
168 | - | |
169 | ++words_offset; | |
170 | error = parse_backtick (&word, &word_length, &max_length, words, | |
171 | &words_offset, flags, pwordexp, ifs, | |
172 | -- | |
173 | 2.2.1 | |
174 |