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CDRIVER-6134 check SASL username length #2156

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Merged
merged 1 commit into from
Oct 22, 2025
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CDRIVER-6134 check SASL username length #2156

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12 changes: 10 additions & 2 deletions src/libmongoc/src/mongoc/mongoc-cyrus.c
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Original file line number Diff line number Diff line change
Expand Up @@ -112,10 +112,18 @@ _mongoc_cyrus_canon_user(sasl_conn_t *conn,
BSON_UNUSED(sasl);
BSON_UNUSED(flags);
BSON_UNUSED(user_realm);
BSON_UNUSED(out_max);

// `inlen` is a string length (excluding trailing NULL).
// Cyrus-SASL passes an `out` buffer of size `out_max + 1`. Assume `out_max` is the max to be safe.
if (inlen + 1 >= out_max) {
MONGOC_ERROR("SASL username too large");
return SASL_BUFOVER;
}

TRACE("Canonicalizing %s (%" PRIu32 ")\n", in, inlen);
strcpy(out, in);
// Use memmove in case buffers overlap. From Cyrus-SASL: "output buffers and the input buffers may be the same"
memmove(out, in, inlen);
out[inlen] = '\0';
*out_len = inlen;
return SASL_OK;
}
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