Inconsistent behavior of session variable max_allowed_packet
(and net_buffer_length); only assignment to the global variable
has any effect, without this being obvious to the user.
The patch for Bug#22891 is backported to 5.0, making the two
session variables read-only. As this is a backport to GA
software, the error used when trying to assign to the read-
only variable is ER_UNKNOWN_ERROR. The error message is the
same as in 5.1+.
warnings after uncompressed_length
UNCOMPRESSED_LENGTH() did not validate its argument. In
particular, if the argument length was less than 4 bytes,
an uninitialized memory value was returned as a result.
Since the result of COMPRESS() is either an empty string or
a 4-byte length prefix followed by compressed data, the bug was
fixed by ensuring that the argument of UNCOMPRESSED_LENGTH() is
either an empty string or contains at least 5 bytes (as done in
UNCOMPRESS()). This is the best we can do to validate input
without decompressing.
