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gunicode: Fix UB in gutf8.c and utf8-pointer test

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In glib/gutf8.c there was an UB in function g_utf8_find_prev_char when
p == str. In this case we substract one from p and now p points to a
location outside of the boundary of str. It's a UB by the standard.
Since this function are meant to be fast, we don't check the boundary
conditions.

Fix glib/tests/utf8-pointer test. It failed due to the UB described
above and aggressive optimisation when -O2 and LTO are enabled. Some
compilers (e.g. GCC with major version >= 8) create an optimised version
of g_utf8_find_prev_char with the first argument fixed and stored
somewhere else (with a different pointer). It can be solved with either
marking str as volatile or creating a copy of str in memory. We choose
the second approach since it's more explicit solution.

Add additional checks to glib/tests/utf8-pointer test.

Closes #1917
This commit is contained in:
nightuser 2019-11-14 18:38:03 +00:00 committed by Philip Withnall
parent 4dcad56fb2
commit b555119ca3
2 changed files with 76 additions and 38 deletions
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7
glib/gutf8.c
View File

@ -139,11 +139,12 @@ const gchar * const g_utf8_skip = utf8_skip_data;
* Returns: (transfer none) (nullable): a pointer to the found character or %NULL.
*/
gchar *
g_utf8_find_prev_char (const char *str,
const char *p)
g_utf8_find_prev_char (const gchar *str,
const gchar *p)
{
for (--p; p >= str; --p)
while (p > str)
{
--p;
if ((*p & 0xc0) != 0x80)
return (gchar *)p;
}

107
glib/tests/utf8-pointer.c
View File

@ -97,46 +97,83 @@ test_find (void)
* U+0041 Latin Capital Letter A (\101)
* U+1EB6 Latin Capital Letter A With Breve And Dot Below (\341\272\266)
*/
const gchar *str = "\340\254\213\360\220\244\200\101\341\272\266\0\101";
const gchar *p = str + strlen (str);
#define TEST_STR "\340\254\213\360\220\244\200\101\341\272\266\0\101"
const gsize str_size = sizeof TEST_STR;
const gchar *str = TEST_STR;
const gchar str_array[] = TEST_STR;
const gchar * volatile str_volatile = TEST_STR;
#undef TEST_STR
gchar *str_copy = g_malloc (str_size);
const gchar *p;
const gchar *q;
memcpy (str_copy, str, str_size);
q = g_utf8_find_prev_char (str, p);
g_assert (q == str + 8);
q = g_utf8_find_prev_char (str, q);
g_assert (q == str + 7);
q = g_utf8_find_prev_char (str, q);
g_assert (q == str + 3);
q = g_utf8_find_prev_char (str, q);
g_assert (q == str);
q = g_utf8_find_prev_char (str, q);
g_assert (q == NULL);
#define TEST_SET(STR) \
G_STMT_START { \
p = STR + (str_size - 1); \
\
q = g_utf8_find_prev_char (STR, p); \
g_assert (q == STR + 12); \
q = g_utf8_find_prev_char (STR, q); \
g_assert (q == STR + 11); \
q = g_utf8_find_prev_char (STR, q); \
g_assert (q == STR + 8); \
q = g_utf8_find_prev_char (STR, q); \
g_assert (q == STR + 7); \
q = g_utf8_find_prev_char (STR, q); \
g_assert (q == STR + 3); \
q = g_utf8_find_prev_char (STR, q); \
g_assert (q == STR); \
q = g_utf8_find_prev_char (STR, q); \
g_assert_null (q); \
\
p = STR + 4; \
q = g_utf8_find_prev_char (STR, p); \
g_assert (q == STR + 3); \
\
p = STR + 2; \
q = g_utf8_find_prev_char (STR, p); \
g_assert (q == STR); \
\
p = STR + 2; \
q = g_utf8_find_next_char (p, NULL); \
g_assert (q == STR + 3); \
q = g_utf8_find_next_char (q, NULL); \
g_assert (q == STR + 7); \
\
q = g_utf8_find_next_char (p, STR + 6); \
g_assert (q == STR + 3); \
q = g_utf8_find_next_char (q, STR + 6); \
g_assert_null (q); \
\
q = g_utf8_find_next_char (STR, STR); \
g_assert_null (q); \
\
q = g_utf8_find_next_char (STR + strlen (STR), NULL); \
g_assert (q == STR + strlen (STR) + 1); \
\
/* Check return values when reaching the end of the string, \
* with @end set and unset. */ \
q = g_utf8_find_next_char (STR + 10, NULL); \
g_assert_nonnull (q); \
g_assert (*q == '\0'); \
\
q = g_utf8_find_next_char (STR + 10, STR + 11); \
g_assert_null (q); \
} G_STMT_END
p = str + 2;
q = g_utf8_find_next_char (p, NULL);
g_assert (q == str + 3);
q = g_utf8_find_next_char (q, NULL);
g_assert (q == str + 7);
TEST_SET(str_array);
TEST_SET(str_copy);
TEST_SET(str_volatile);
/* Starting with GCC 8 tests on @str with "-O2 -flto" in CFLAGS fail due to
* (incorrect?) constant propagation of @str into @g_utf8_find_prev_char. It
* doesn't happen if @TEST_STR doesn't contain \0 in the middle but the tests
* should cover all corner cases.
* For instance, see https://gitlab.gnome.org/GNOME/glib/issues/1917 */
q = g_utf8_find_next_char (p, str + 6);
g_assert (q == str + 3);
q = g_utf8_find_next_char (q, str + 6);
g_assert (q == NULL);
#undef TEST_SET
q = g_utf8_find_next_char (str, str);
g_assert (q == NULL);
q = g_utf8_find_next_char (str + strlen (str), NULL);
g_assert (q == str + strlen (str) + 1);
/* Check return values when reaching the end of the string,
* with @end set and unset. */
q = g_utf8_find_next_char (str + 10, NULL);
g_assert_nonnull (q);
g_assert (*q == '\0');
q = g_utf8_find_next_char (str + 10, str + 11);
g_assert_null (q);
g_free (str_copy);
}
int main (int argc, char *argv[])