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bpo-34736: improve error message for invalid length b64decode inputs #9563

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Merged
merged 1 commit into from
Sep 28, 2018
Merged

bpo-34736: improve error message for invalid length b64decode inputs #9563

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6 changes: 5 additions & 1 deletion Lib/test/test_binascii.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
import unittest
import binascii
import array
import re

# Note: "*_hex" functions are aliases for "(un)hexlify"
b2a_functions = ['b2a_base64', 'b2a_hex', 'b2a_hqx', 'b2a_qp', 'b2a_uu',
Expand Down Expand Up @@ -127,7 +128,10 @@ def assertIncorrectPadding(data):

# Test base64 with invalid number of valid characters (1 mod 4)
def assertInvalidLength(data):
with self.assertRaisesRegex(binascii.Error, r'(?i)invalid.+length'):
n_data_chars = len(re.sub(br'[^A-Za-z0-9/+]', br'', data))
expected_errmsg_re = \
r'(?i)Invalid.+number of data characters.+' + str(n_data_chars)
with self.assertRaisesRegex(binascii.Error, expected_errmsg_re):
binascii.a2b_base64(self.type2test(data))

assertInvalidLength(b'a')
Expand Down
10 changes: 7 additions & 3 deletions Modules/binascii.c
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Expand Up @@ -438,6 +438,7 @@ binascii_a2b_base64_impl(PyObject *module, Py_buffer *data)
{
const unsigned char *ascii_data;
unsigned char *bin_data;
unsigned char *bin_data_start;
int leftbits = 0;
unsigned char this_ch;
unsigned int leftchar = 0;
Expand All @@ -461,6 +462,7 @@ binascii_a2b_base64_impl(PyObject *module, Py_buffer *data)
bin_data = _PyBytesWriter_Alloc(&writer, bin_len);
if (bin_data == NULL)
return NULL;
bin_data_start = bin_data;

for( ; ascii_len > 0; ascii_len--, ascii_data++) {
this_ch = *ascii_data;
Expand Down Expand Up @@ -516,9 +518,11 @@ binascii_a2b_base64_impl(PyObject *module, Py_buffer *data)
** This is an invalid length, as there is no possible input that
** could encoded into such a base64 string.
*/
PyErr_SetString(Error,
"Invalid base64-encoded string: "
"length cannot be 1 more than a multiple of 4");
PyErr_Format(Error,
"Invalid base64-encoded string: "
"number of data characters (%d) cannot be 1 more "
"than a multiple of 4",
(bin_data - bin_data_start) / 3 * 4 + 1);
} else {
PyErr_SetString(Error, "Incorrect padding");
}
Expand Down