Re: [PATCH] sparse-checkout: use fdopen_lock_file() instead of xfdopen()

Patrick Steinhardt [off-list ref] writes:

quoted

+	if (commit_lock_file(&lk))
+		die_errno(_("unable to write %s"), get_locked_file_path(&lk));
 
 	clear_pattern_list(pl);

I think the error handling is broken. `commit_lock_file()` calls
`rename_tempfile()`, which deletes the temporary file even in the error
case. The consequence is that `lk->tempfile` will be set to the `NULL`
pointer. When we call `get_locked_file_path()` we then dereference it
unconditionally and would thus segfault.

Hmph.  Would this be sufficient as a band-aid, then?

 builtin/sparse-checkout.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git c/builtin/sparse-checkout.c w/builtin/sparse-checkout.c
index f1bd31b2f7..60363fd056 100644
--- c/builtin/sparse-checkout.c
+++ w/builtin/sparse-checkout.c

@@ -356,7 +356,7 @@ static int write_patterns_and_update(struct pattern_list *pl)
 		write_patterns_to_file(fp, pl);
 
 	if (commit_lock_file(&lk))
-		die_errno(_("unable to write %s"), get_locked_file_path(&lk));
+		die_errno(_("unable to write %s"), sparse_filename);
 
 	clear_pattern_list(pl);