From 4015fae044ce52a639c9358e22a9e948f287c89f Mon Sep 17 00:00:00 2001 From: Jay Satiro Date: Mon, 11 Feb 2019 23:00:00 -0500 Subject: [PATCH] connection_check: restore original conn->data after the check - Save the original conn->data before it's changed to the specified data transfer for the connection check and then restore it afterwards. This is a follow-up to 38d8e1b 2019-02-11. History: It was discovered a month ago that before checking whether to extract a dead connection that that connection should be associated with a "live" transfer for the check (ie original conn->data ignored and set to the passed in data). A fix was landed in 54b201b which did that and also cleared conn->data after the check. The original conn->data was not restored, so presumably it was thought that a valid conn->data was no longer needed. Several days later it was discovered that a valid conn->data was needed after the check and follow-up fix was landed in bbae24c which partially reverted the original fix and attempted to limit the scope of when conn->data was changed to only when pruning dead connections. In that case conn->data was not cleared and the original conn->data not restored. A month later it was discovered that the original fix was somewhat correct; a "live" transfer is needed for the check in all cases because original conn->data could be null which could cause a bad deref at arbitrary points in the check. A fix was landed in 38d8e1b which expanded the scope to all cases. conn->data was not cleared and the original conn->data not restored. A day later it was discovered that not restoring the original conn->data may lead to busy loops in applications that use the event interface, and given this observation it's a pretty safe assumption that there is some code path that still needs the original conn->data. This commit is the follow-up fix for that, it restores the original conn->data after the connection check. Assisted-by: tholin@users.noreply.github.com Reported-by: tholin@users.noreply.github.com Fixes https://github.com/curl/curl/issues/3542 Closes #3559 --- lib/url.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/lib/url.c b/lib/url.c index bc47685db..46c8fb5fb 100644 --- a/lib/url.c +++ b/lib/url.c @@ -964,8 +964,10 @@ static bool extract_if_dead(struct connectdata *conn, /* The protocol has a special method for checking the state of the connection. Use it to check if the connection is dead. */ unsigned int state; + struct Curl_easy *olddata = conn->data; conn->data = data; /* use this transfer for now */ state = conn->handler->connection_check(conn, CONNCHECK_ISDEAD); + conn->data = olddata; dead = (state & CONNRESULT_DEAD); } else { @@ -994,7 +996,6 @@ struct prunedead { static int call_extract_if_dead(struct connectdata *conn, void *param) { struct prunedead *p = (struct prunedead *)param; - conn->data = p->data; /* transfer to use for this check */ if(extract_if_dead(conn, p->data)) { /* stop the iteration here, pass back the connection that was extracted */ p->extracted = conn;