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Make asynchronous agent_query() requests cancellable.

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Now, instead of returning a boolean indicating whether the query has
completed or is still pending, agent_query() returns NULL to indicate
that the query _has_ completed, and if it hasn't, it returns a pointer
to a context structure representing the pending query, so that the
latter can be used to cancel the query if (for example) you later
decide you need to free the thing its callback was using as a context.

This should fix a potential race-condition segfault if you overload an
agent forwarding channel and then close it abruptly. (Which nobody
will be doing for sensible purposes, of course! But I ran across this
while stress-testing other aspects of agent forwarding.)
This commit is contained in:
Simon Tatham
2017-01-29 20:24:15 +00:00
parent f864265e39
commit eb2fe29fc9
7 changed files with 140 additions and 71 deletions
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16
windows/winpgntc.c
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@ -24,8 +24,14 @@ int agent_exists(void)
return TRUE;
}
int agent_query(void *in, int inlen, void **out, int *outlen,
void (*callback)(void *, void *, int), void *callback_ctx)
void agent_cancel_query(agent_pending_query *q)
{
assert(0 && "Windows agent queries are never asynchronous!");
}
agent_pending_query *agent_query(
void *in, int inlen, void **out, int *outlen,
void (*callback)(void *, void *, int), void *callback_ctx)
{
HWND hwnd;
char *mapname;
@ -42,7 +48,7 @@ int agent_query(void *in, int inlen, void **out, int *outlen,
hwnd = FindWindow("Pageant", "Pageant");
if (!hwnd)
return 1; /* *out == NULL, so failure */
return NULL; /* *out == NULL, so failure */
mapname = dupprintf("PageantRequest%08x", (unsigned)GetCurrentThreadId());
psa = NULL;
@ -83,7 +89,7 @@ int agent_query(void *in, int inlen, void **out, int *outlen,
0, AGENT_MAX_MSGLEN, mapname);
if (filemap == NULL || filemap == INVALID_HANDLE_VALUE) {
sfree(mapname);
return 1; /* *out == NULL, so failure */
return NULL; /* *out == NULL, so failure */
}
p = MapViewOfFile(filemap, FILE_MAP_WRITE, 0, 0, 0);
memcpy(p, in, inlen);
@ -111,5 +117,5 @@ int agent_query(void *in, int inlen, void **out, int *outlen,
sfree(mapname);
if (psd)
LocalFree(psd);
return 1;
return NULL;
}