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gh-118314: Fix padding edge case in binascii.a2b_base64 strict mode (GH-118320)

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Fix an edge case in `binascii.a2b_base64` strict mode, where
excessive padding was not detected when no padding is necessary.

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>
Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>
This commit is contained in:
Youfu Zhang 2024-05-07 17:18:45 +08:00 • committed by GitHub
parent 3a6ff1b1d9
commit fe47d9bee3
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7
Modules/binascii.c
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@ -414,6 +414,13 @@ binascii_a2b_base64_impl(PyObject *module, Py_buffer *data, int strict_mode)
if (this_ch == BASE64_PAD) {
padding_started = 1;
if (strict_mode && quad_pos == 0) {
state = get_binascii_state(module);
if (state) {
PyErr_SetString(state->Error, "Excess padding not allowed");
}
goto error_end;
}
if (quad_pos >= 2 && quad_pos + ++pads >= 4) {
/* A pad sequence means we should not parse more input.
** We've already interpreted the data from the quad at this point.