[PATCH 03/11] remote: guard `remote_tracking()` against NULL remote

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

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

The `remote_tracking()` function unconditionally dereferences
`remote->fetch` without checking whether remote is NULL.

In practice, this never happens because the only caller (`apply_cas()`)
guards the calls to this function by checking the `use_tracking` and
`use_tracking_for_rest` attributes.

However, it requires quite involved reasoning to reach that conclusion,
and is therefore fragile. Just return -1 ("no tracking ref") when there
is no remote to work with.

Pointed out by Coverity.

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

diff --git a/remote.c b/remote.c
index 00723b385e..34d0367f11 100644
--- a/remote.c
+++ b/remote.c
@@ -2681,6 +2681,8 @@ static int remote_tracking(struct remote *remote, const char *refname,
 {
 	char *dst;
 
+	if (!remote)
+		return -1; /* no remote to look up tracking ref */
 	dst = apply_refspecs(&remote->fetch, refname);
 	if (!dst)
 		return -1; /* no tracking ref for refname at remote */
-- 
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