[PATCH v3 01/12] http: die on curl_easy_duphandle failure in get_active_slot

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

get_active_slot() duplicates the default curl handle via
curl_easy_duphandle() to create a per-slot session handle. The
return value is stored directly in slot->curl without checking
for NULL. curl_easy_duphandle() can return NULL when memory
allocation fails internally, and the libcurl documentation
explicitly states this possibility.

When this happens, slot->curl is NULL and the very next operation
(curl_easy_setopt on line 1632 for CURLOPT_COOKIEFILE) passes
NULL as the curl handle, which is undefined behavior in libcurl
and typically crashes.

Every HTTP operation in git goes through get_active_slot(), so
this affects all remote-https, remote-http, and HTTP-based
operations (clone, fetch, push over HTTP, bundle-uri downloads).

Add a NULL check and die() with a clear message. There is no
reasonable recovery from a failed handle duplication: the process
is out of memory and cannot perform any HTTP operation.

Pointed out by Coverity.

Assisted-by: Claude Opus 4.6
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 http.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/http.c b/http.c
index b4e7b8d00b..8f1d6d1f56 100644
--- a/http.c
+++ b/http.c
@@ -1608,6 +1608,8 @@ struct active_request_slot *get_active_slot(void)
 
 	if (!slot->curl) {
 		slot->curl = curl_easy_duphandle(curl_default);
+		if (!slot->curl)
+			die("curl_easy_duphandle failed");
 		curl_session_count++;
 	}
 
-- 
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