Commit 7fafec0e53f8711b73912d46b43451c599aeceb3
2018-10-29T18:32:39
tree: fix integer overflow when reading unreasonably large filemodes The `parse_mode` option uses an open-coded octal number parser. The parser is quite naive in that it simply parses until hitting a character that is not in the accepted range of '0' - '7', completely ignoring the fact that we can at most accept a 16 bit unsigned integer as filemode. If the filemode is bigger than UINT16_MAX, it will thus overflow and provide an invalid filemode for the object entry. Fix the issue by using `git__strntol32` instead and doing a bounds check. As this function already handles overflows, it neatly solves the problem. Note that previously, `parse_mode` was also skipping the character immediately after the filemode. In proper trees, this should be a simple space, but in fact the parser accepted any character and simply skipped over it. As a consequence of using `git__strntol32`, we now need to an explicit check for a trailing whitespace after having parsed the filemode. Because of the newly introduced error message, the test object::tree::parse::mode_doesnt_cause_oob_read needs adjustment to its error message check, which in fact is a good thing as it demonstrates that we now fail looking for the whitespace immediately following the filemode. Add a test that shows that we will fail to parse such invalid filemodes now.
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diff --git a/src/tree.c b/src/tree.c
index 9772f5a..d9b5939 100644
--- a/src/tree.c
+++ b/src/tree.c
@@ -356,22 +356,21 @@ static int tree_error(const char *str, const char *path)
return -1;
}
-static int parse_mode(unsigned int *modep, const char *buffer, size_t buffer_len, const char **buffer_out)
+static int parse_mode(uint16_t *mode_out, const char *buffer, size_t buffer_len, const char **buffer_out)
{
- const char *buffer_end = buffer + buffer_len;
- unsigned char c;
- unsigned int mode = 0;
+ int32_t mode;
+ int error;
- if (*buffer == ' ')
+ if (!buffer_len || git__isspace(*buffer))
return -1;
- while (buffer < buffer_end && (c = *buffer++) != ' ') {
- if (c < '0' || c > '7')
- return -1;
- mode = (mode << 3) + (c - '0');
- }
- *modep = mode;
- *buffer_out = buffer;
+ if ((error = git__strntol32(&mode, buffer, buffer_len, buffer_out, 8)) < 0)
+ return error;
+
+ if (mode < 0 || mode > UINT16_MAX)
+ return -1;
+
+ *mode_out = mode;
return 0;
}
@@ -393,11 +392,14 @@ int git_tree__parse_raw(void *_tree, const char *data, size_t size)
git_tree_entry *entry;
size_t filename_len;
const char *nul;
- unsigned int attr;
+ uint16_t attr;
if (parse_mode(&attr, buffer, buffer_end - buffer, &buffer) < 0 || !buffer)
return tree_error("failed to parse tree: can't parse filemode", NULL);
+ if (buffer >= buffer_end || (*buffer++) != ' ')
+ return tree_error("failed to parse tree: missing space after filemode", NULL);
+
if ((nul = memchr(buffer, 0, buffer_end - buffer)) == NULL)
return tree_error("failed to parse tree: object is corrupted", NULL);
diff --git a/tests/object/tree/parse.c b/tests/object/tree/parse.c
index 67b7586..83d2219 100644
--- a/tests/object/tree/parse.c
+++ b/tests/object/tree/parse.c
@@ -118,7 +118,13 @@ void test_object_tree_parse__mode_doesnt_cause_oob_read(void)
* later fail to parse the OID with a different error
* message
*/
- cl_assert(strstr(giterr_last()->message, "object is corrupted"));
+ cl_assert_equal_s(giterr_last()->message, "failed to parse tree: missing space after filemode");
+}
+
+void test_object_tree_parse__unreasonably_large_mode_fails(void)
+{
+ const char data[] = "10000000000000000000000000 bar\x00" OID1_HEX;
+ assert_tree_fails(data, ARRAY_SIZE(data) - 1);
}
void test_object_tree_parse__missing_filename_separator_fails(void)