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gh-101178: Fix possible integer overflow in Ascii85 encoder with wrapcol=1 #144778

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gh-101178: Fix possible integer overflow in Ascii85 encoder with wrapcol=1 #144778

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25 changes: 8 additions & 17 deletions Modules/binascii.c
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Original file line number Diff line number Diff line change
Expand Up @@ -785,22 +785,21 @@ binascii_b2a_base64_impl(PyObject *module, Py_buffer *data, size_t wrapcol,
* Use unsigned integer arithmetic to avoid signed integer overflow.
*/
size_t out_len = ((size_t)bin_len + 2u) / 3u * 4u;
if (out_len > PY_SSIZE_T_MAX) {
goto toolong;
}
if (wrapcol && out_len) {
/* Each line should encode a whole number of bytes. */
wrapcol = wrapcol < 4 ? 4 : wrapcol / 4 * 4;
out_len += (out_len - 1u) / wrapcol;
if (out_len > PY_SSIZE_T_MAX) {
goto toolong;
}
}
if (newline) {
out_len++;
if (out_len > PY_SSIZE_T_MAX) {
goto toolong;
}
if (out_len > PY_SSIZE_T_MAX) {
binascii_state *state = get_binascii_state(module);
if (state == NULL) {
return NULL;
}
PyErr_SetString(state->Error, "Too much data for base64");
return NULL;
}
PyBytesWriter *writer = PyBytesWriter_Create(out_len);
if (writer == NULL) {
Expand Down Expand Up @@ -841,14 +840,6 @@ binascii_b2a_base64_impl(PyObject *module, Py_buffer *data, size_t wrapcol,
*ascii_data++ = '\n'; /* Append a courtesy newline */

return PyBytesWriter_FinishWithPointer(writer, ascii_data);

toolong:;
binascii_state *state = get_binascii_state(module);
if (state == NULL) {
return NULL;
}
PyErr_SetString(state->Error, "Too much data for base64");
return NULL;
}

/*[clinic input]
Expand Down Expand Up @@ -1046,7 +1037,7 @@ binascii_b2a_ascii85_impl(PyObject *module, Py_buffer *data, int foldspaces,
if (!pad && (bin_len % 4)) {
out_len -= 4 - (bin_len % 4);
}
if (wrapcol && out_len) {
if (wrapcol && out_len && out_len <= PY_SSIZE_T_MAX) {
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@sethmlarson sethmlarson Feb 13, 2026

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Let me know if I'm misunderstanding, but wouldn't we need to "error out" if the out_len would overflow here instead of not expanding? The larger amount of data will still be written outside ascii_data whether out_len is expanded or not?

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@serhiy-storchaka serhiy-storchaka Feb 14, 2026

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We error out in the next "if".

out_len += (out_len - 1) / wrapcol;
}
if (out_len > PY_SSIZE_T_MAX) {
Expand Down
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