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Commite7ff968

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libpq: Be strict about cancel key lengths
The protocol documentation states that the maximum length of a cancelkey is 256 bytes. This starts checking for that limit in libpq.Otherwise third party backend implementations will probably startusing more bytes anyway. We also start requiring that a protocol 3.0connection does not send a longer cancel key, to make sure thatservers don't start breaking old 3.0-only clients by accident. Finallythis also restricts the minimum key length to 4 bytes (both in theprotocol spec and in the libpq implementation).Author: Jelte Fennema-Nio <postgres@jeltef.nl>Reviewed-by: Jacob Champion <jchampion@postgresql.org>Discussion:https://www.postgresql.org/message-id/df892f9f-5923-4046-9d6f-8c48d8980b50@iki.fiBackpatch-through: 18
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‎doc/src/sgml/protocol.sgml‎

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Original file line numberDiff line numberDiff line change
@@ -4163,7 +4163,7 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
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message, indicated by the length field.
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</para>
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<para>
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The maximum key lengthis256 bytes. The
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Theminimum andmaximum key lengthare 4 and256 bytes, respectively. The
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<productname>PostgreSQL</productname> server only sends keys up to
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32 bytes, but the larger maximum size allows for future server
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versions, as well as connection poolers and other middleware, to use

‎src/interfaces/libpq/fe-protocol3.c‎

Lines changed: 21 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1569,6 +1569,27 @@ getBackendKeyData(PGconn *conn, int msgLength)
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cancel_key_len=5+msgLength- (conn->inCursor-conn->inStart);
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if (cancel_key_len!=4&&conn->pversion==PG_PROTOCOL(3,0))
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{
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libpq_append_conn_error(conn,"received invalid BackendKeyData message: cancel key with length %d not allowed in protocol version 3.0 (must be 4 bytes)",cancel_key_len);
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handleFatalError(conn);
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return0;
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}
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if (cancel_key_len<4)
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{
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libpq_append_conn_error(conn,"received invalid BackendKeyData message: cancel key with length %d is too short (minimum 4 bytes)",cancel_key_len);
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handleFatalError(conn);
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return0;
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}
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if (cancel_key_len>256)
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{
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libpq_append_conn_error(conn,"received invalid BackendKeyData message: cancel key with length %d is too long (maximum 256 bytes)",cancel_key_len);
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handleFatalError(conn);
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return0;
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}
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conn->be_cancel_key=malloc(cancel_key_len);
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if (conn->be_cancel_key==NULL)
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{

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