[mysqlnd] Fix OK packet message length buffer over-read - #287
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The OK packet message-length varint is read after the last bounds check, so a length-encoded integer at the end of a packet can advance p past header.size and even past the end of the 4096-byte command buffer. The old MIN(net_len, buf_len - (p - begin)) clamp then underflows and passes an unclamped attacker-controlled length to mnd_pestrndup(), reading heap memory beyond both the packet and its allocation; even in the non- overflowing case the message was filled with stale command-buffer bytes. Bail out via BAIL_IF_NO_MORE_DATA once the varint advances p past the payload and clamp against header.size instead of buf_len, matching the hardening already applied to php_mysqlnd_auth_response_read() and the other packet readers by GHSA-h35g-vwh6-m678; an audit found no further readers using the vulnerable buf_len clamp.
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php_mysqlnd_ok_read() reads the length-encoded message length after its last bounds check, so a malicious server can place the varint at the very end of an OK packet that fills the 4096-byte command buffer. The varint read then advances p past header.size and past the end of the command buffer, the old MIN(net_len, buf_len - (p - begin)) clamp underflows to a huge value, and mnd_pestrndup() copies an unclamped attacker-controlled number of bytes from beyond the allocation; with smaller packets the message is filled with stale command-buffer content, which the new fake-server test demonstrates as mysqli_info() returning leftover greeting bytes. The fix bails out via BAIL_IF_NO_MORE_DATA once p moves past the payload and clamps against header.size instead of buf_len, mirroring the hardening GHSA-h35g-vwh6-m678 already applied to the auth response and result-set readers; an audit found no other readers still using the vulnerable buf_len clamp.