Commit 4308f5d3 authored by Aaron Plattner's avatar Aaron Plattner

os: Don't crash in AttendClient if the client is gone

If a client is in the process of being closed down, then its client->osPrivate
pointer will be set to NULL by CloseDownConnection. This can cause a crash if
freeing the client's resources results in a call to AttendClient. For example,
if the client has a pending sync fence:

 Thread 1 "X" received signal SIGSEGV, Segmentation fault.
 AttendClient (client=0x5571c4aed9a0) at ../os/connection.c:942
 (gdb) bt
 #0  AttendClient (client=0x5571c4aed9a0) at ../os/connection.c:942
 #1  0x00005571c3dbb865 in SyncAwaitTriggerFired (pTrigger=<optimized out>) at ../Xext/sync.c:694
 #2  0x00005571c3dd5749 in miSyncDestroyFence (pFence=0x5571c5063980) at ../miext/sync/misync.c:120
 #3  0x00005571c3dbbc69 in FreeFence (obj=<optimized out>, id=<optimized out>) at ../Xext/sync.c:1909
 #4  0x00005571c3d7a01d in doFreeResource (res=0x5571c506e3d0, skip=skip@entry=0) at ../dix/resource.c:880
 #5  0x00005571c3d7b1dc in FreeClientResources (client=0x5571c4aed9a0) at ../dix/resource.c:1146
 #6  FreeClientResources (client=0x5571c4aed9a0) at ../dix/resource.c:1109
 #7  0x00005571c3d5525f in CloseDownClient (client=0x5571c4aed9a0) at ../dix/dispatch.c:3473
 #8  0x00005571c3d55eeb in Dispatch () at ../dix/dispatch.c:492
 #9  0x00005571c3d59e96 in dix_main (argc=3, argv=0x7ffe7854bc28, envp=<optimized out>) at ../dix/main.c:276
 #10 0x00007fea4837cb6b in __libc_start_main (main=0x5571c3d1d060 <main>, argc=3, argv=0x7ffe7854bc28, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffe7854bc18) at ../csu/libc-start.c:308
 #11 0x00005571c3d1d09a in _start () at ../Xext/sync.c:2378
 (gdb) print client->osPrivate
 $1 = (void *) 0x0

Since the client is about to be freed, its ignore count doesn't matter and
AttendClient can simply be a no-op. Check for client->clientGone in AttendClient
and remove similar checks from two callers that had them.
Signed-off-by: Aaron Plattner's avatarAaron Plattner <aplattner@nvidia.com>
parent 66da95a1
......@@ -125,8 +125,7 @@ ClientSleepUntil(ClientPtr client,
static void
ClientAwaken(ClientPtr client, void *closure)
{
if (!client->clientGone)
AttendClient(client);
AttendClient(client);
}
static int
......
......@@ -662,14 +662,7 @@ ClientWakeup(ClientPtr client)
if (q->client == client) {
*prev = q->next;
free(q);
if (client->clientGone)
/* Oops -- new zombie cleanup code ensures this only
* happens from inside CloseDownClient; don't want to
* recurse here...
*/
/* CloseDownClient(client) */ ;
else
AttendClient(client);
AttendClient(client);
break;
}
prev = &q->next;
......
......@@ -924,6 +924,14 @@ AttendClient(ClientPtr client)
{
OsCommPtr oc = (OsCommPtr) client->osPrivate;
if (client->clientGone) {
/*
* client is gone, so any pending requests will be dropped and its
* ignore count doesn't matter.
*/
return;
}
client->ignoreCount--;
if (client->ignoreCount)
return;
......
......@@ -2362,9 +2362,9 @@ RecordDisableContext(RecordContextPtr pContext)
if (!pContext->pRecordingClient->clientGone) {
RecordAProtocolElement(pContext, NULL, XRecordEndOfData, NULL, 0, 0, 0);
RecordFlushReplyBuffer(pContext, NULL, 0, NULL, 0);
/* Re-enable request processing on this connection. */
AttendClient(pContext->pRecordingClient);
}
/* Re-enable request processing on this connection. */
AttendClient(pContext->pRecordingClient);
for (pRCAP = pContext->pListOfRCAP; pRCAP; pRCAP = pRCAP->pNextRCAP) {
RecordUninstallHooks(pRCAP, 0);
......
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