Kristian Nielsen 5dd6b9252b MDEV-35691: Invalid access, use-after-free, on rli->description_event_for_exec ...

This commit rewrites the rpl_master_has_bug() mechanism to solve a problem
with invalid memory access. The rpl_master_has_bug() mechanism detects
certain bugs depending on the master version, and uses that to enable
specific work-arounds on the slave. The problem was that
rpl_master_has_bug() accessed Relay_log_info::description_event_for_exec
that is not valid to access from concurrent parallel replication worker
threads, only from the SQL driver thread. Thus it could use the wrong event
or access invalid/freed memory.

This patch instead computes a bitmask of detected bugs when the SQL driver
thread processes the format description event, and reads that bitmask with
an atomic load from the worker threads. The bitmask of bugs can only change
when the master restarts with a new version, and we do not replicate events
concurrently across a format description event from a master restart. Thus,
the bitmask is safe to read concurrently from the Relay_log_info object
without locking.

This also avoids an expensive match of each entry in the bug list against
the master server version done for every single call to
rpl_master_has_bug(), which could be quite expensive when done eg. per field
in row events as in Field_string::compatible_field_size().

Also remove redundant conditional in table_def::compatible_with().

Thanks to Andrei Elkin for the idea to safely read the bitmask
concurrently from the Relay_log_info.

Reviewed-by: Andrei Elkin <andrei.elkin@pp.inet.fi>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>

2026-09-03 08:16:29 +02:00

185 KiB

Raw Permalink Blame History

View Raw