Much like MULTI/EXEC/DISCARD, the WATCH and UNWATCH are not actually
operating on the database or server state, but instead operate on the
client state. the client may send them all in one long pipeline and check
all the responses only at the end, so failing them may lead to a
mismatch between the client state on the server and the one on the
client end, and execute the wrong commands (ones that were meant to be
discarded)
the watched keys are not actually stored in the client struct, but they
are in fact part of the client state. for instance, they're not cleared
or moved in SWAPDB or FLUSHDB.
the recent change in that loop (iteration rather than waiting for it to
be empty) was intended to avoid an endless loop in case some slave would
refuse to be freed.
but the lookup of the first client remained, which would have caused it
to try the first one again and again instead of moving on.
This impacts client verification for chained certificates (such as Lets
Encrypt certificates). Client Verify requires the full chain in order to
properly verify the certificate.
`clusterStartHandshake` will start hand handshake
and eventually send CLUSTER MEET message, which is strictly prohibited
in the REDIS CLUSTER SPEC.
Only system administrator can initiate CLUSTER MEET message.
Futher, according to the SPEC, rather than IP/PORT pairs, only nodeid
can be trusted.
Now it is also possible for ACL SETUSER to accept empty strings
as valid operations (doing nothing), so for instance
ACL SETUSER myuser ""
Will have just the effect of creating a user in the default state.
This should fix#7329.
After a closer look, the Redis core devleopers all believe that this was
too fragile, caused many bugs that we didn't expect and that were very
hard to track. Better to find an alternative solution that is simpler.
We want to react a bit more aggressively if we sense that the master is
sending us some corrupted stream. By setting the protocol error we both
ensure that the replica will disconnect, and avoid caching the master so
that a full SYNC will be required. This is protective against
replication bugs.
After adjustMeaningfulReplOffset(), all the other related variable
should be updated, including server.second_replid_offset.
Or the old version redis like 5.0 may receive wrong data from
replication stream, cause redis 5.0 can sync with redis 6.0,
but doesn't know meaningful offset.
Otherwise we run into that:
Backtrace:
src/redis-server 127.0.0.1:21322(logStackTrace+0x45)[0x479035]
src/redis-server 127.0.0.1:21322(sigsegvHandler+0xb9)[0x4797f9]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x11390)[0x7fd373c5e390]
src/redis-server 127.0.0.1:21322(_serverAssert+0x6a)[0x47660a]
src/redis-server 127.0.0.1:21322(freeReplicationBacklog+0x42)[0x451282]
src/redis-server 127.0.0.1:21322[0x4552d4]
src/redis-server 127.0.0.1:21322[0x4c5593]
src/redis-server 127.0.0.1:21322(aeProcessEvents+0x2e6)[0x42e786]
src/redis-server 127.0.0.1:21322(aeMain+0x1d)[0x42eb0d]
src/redis-server 127.0.0.1:21322(main+0x4c5)[0x42b145]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7fd3738a3830]
src/redis-server 127.0.0.1:21322(_start+0x29)[0x42b409]
Since we disconnect all the replicas and free the replication backlog in
certain replication paths, and the code that will free the replication
backlog expects that no replica is connected.
However we still need to free the replicas asynchronously in certain
cases, as documented in the top comment of disconnectSlaves().
Citing from the issue:
btw I suggest we change this fix to something else:
* We revert the fix.
* We add a call that disconnects chained replicas in the place where we trim the replica (that is a master i this case) offset.
This way we can avoid disconnections when there is no trimming of the backlog.
Note that we now want to disconnect replicas asynchronously in
disconnectSlaves(), because it's in general safer now that we can call
it from freeClient(). Otherwise for instance the command:
CLIENT KILL TYPE master
May crash: clientCommand() starts running the linked of of clients,
looking for clients to kill. However it finds the master, kills it
calling freeClient(), but this in turn calls replicationCacheMaster()
that may also call disconnectSlaves() now. So the linked list iterator
of the clientCommand() will no longer be valid.
