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Fix possible writes to closed DCBs

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When persistent connections were used, it was possible that the injection
of COM_CHANGE_USER statements caused a crash when a DCB in the wrong state
was accessed.

For MySQL protocol modules, the `data` member of the client DCB points to
the shared session data, a MYSQL_session struct, but for sessions in the
persistent pool, it points to NULL. The boolean, `was_persistent`, tells
whether a DCB was just taken from the pool or it has been in use.

The `was_persistent` status wasn't properly reset for connections that
were put into the pool which caused a COM_CHANGE_USER statement to be
injected for stale connections in the pool which caused a crash when the
NULL `data` member was accessed.
This commit is contained in:
Markus Makela
2016-11-08 09:24:00 +02:00
parent 7358d932e6
commit 689366b6b7
2 changed files with 3 additions and 1 deletions
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1
server/core/dcb.c
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@ -1827,6 +1827,7 @@ dcb_maybe_add_persistent(DCB *dcb)
MXS_DEBUG("%lu [dcb_maybe_add_persistent] Adding DCB to persistent pool, user %s.\n", MXS_DEBUG("%lu [dcb_maybe_add_persistent] Adding DCB to persistent pool, user %s.\n",
pthread_self(), pthread_self(),
dcb->user); dcb->user);
dcb->was_persistent = false;
dcb->dcb_is_zombie = false; dcb->dcb_is_zombie = false;
dcb->persistentstart = time(NULL); dcb->persistentstart = time(NULL);
if (dcb->session) if (dcb->session)

3
server/modules/protocol/MySQL/MySQLBackend/mysql_backend.c
View File

@ -947,8 +947,9 @@ static int gw_MySQLWrite_backend(DCB *dcb, GWBUF *queue)
CHK_DCB(dcb); CHK_DCB(dcb);
spinlock_acquire(&dcb->authlock); spinlock_acquire(&dcb->authlock);
if (dcb->was_persistent) if (dcb->was_persistent && dcb->state == DCB_STATE_POLLING)
{ {
ss_dassert(dcb->persistentstart == 0);
/** /**
* This is a DCB that was just taken out of the persistent connection pool. * This is a DCB that was just taken out of the persistent connection pool.
* We need to sent a COM_CHANGE_USER query to the backend to reset the * We need to sent a COM_CHANGE_USER query to the backend to reset the