pull, fetch: fix segfault in --set-upstream option

avar · gitster · commit 17baeaf82db5 · 2021-12-07T15:19:28.000-08:00
Fix a segfault in the --set-upstream option added in 24bc1a1 (pull, fetch: add --set-upstream option, 2019-08-19) added in v2.24.0. The code added there did not do the same checking we do for "git branch" itself since 8efb889 (branch: segfault fixes and validation, 2013-02-23), which in turn fixed the same sort of segfault I'm fixing now in "git branch --set-upstream-to", see 6183d82 (branch: introduce --set-upstream-to, 2012-08-20). The warning message I'm adding here is an amalgamation of the error added for "git branch" in 8efb889, and the error output install_branch_config() itself emits, i.e. it trims "refs/heads/" from the name and says "branch X on remote", not "branch refs/heads/X on remote". I think it would make more sense to simply die() here, but in the other checks for --set-upstream added in 24bc1a1 we issue a warning() instead. Let's do the same here for consistency for now. There was an earlier submitted alternate way of fixing this in [1], due to that patch breaking threading with the original report at [2] I didn't notice it before authoring this version. I think the more detailed warning message here is better, and we should also have tests for this behavior. The --no-rebase option to "git pull" is needed as of the recently merged 7d0daf3 (Merge branch 'en/pull-conflicting-options', 2021-08-30). 1. https://lore.kernel.org/git/20210706162238.575988-1-clemens@endorphin.org/ 2. https://lore.kernel.org/git/CAG6gW_uHhfNiHGQDgGmb1byMqBA7xa8kuH1mP-wAPEe5Tmi2Ew@mail.gmail.com/ Reported-by: Clemens Fruhwirth <clemens@endorphin.org> Reported-by: Jan Pokorný <poki@fnusa.cz> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/fetch.c b/builtin/fetch.c
@@ -1638,6 +1638,16 @@ static int do_fetch(struct transport *transport,
 			}
 		}
 		if (source_ref) {
+			if (!branch) {
+				const char *shortname = source_ref->name;
+				skip_prefix(shortname, "refs/heads/", &shortname);
+
+				warning(_("could not set upstream of HEAD to '%s' from '%s' when "
+					  "it does not point to any branch."),
+					shortname, transport->remote->name);
+				goto skip;
+			}
+
 			if (!strcmp(source_ref->name, "HEAD") ||
 			    starts_with(source_ref->name, "refs/heads/"))
 				install_branch_config(0,
diff --git a/t/t5553-set-upstream.sh b/t/t5553-set-upstream.sh
@@ -91,6 +91,17 @@ test_expect_success 'fetch --set-upstream with valid URL sets upstream to URL' '
 	check_config_missing other2
 '
 
+test_expect_success 'fetch --set-upstream with a detached HEAD' '
+	git checkout HEAD^0 &&
+	test_when_finished "git checkout -" &&
+	cat >expect <<-\EOF &&
+	warning: could not set upstream of HEAD to '"'"'main'"'"' from '"'"'upstream'"'"' when it does not point to any branch.
+	EOF
+	git fetch --set-upstream upstream main 2>actual.raw &&
+	grep ^warning: actual.raw >actual &&
+	test_cmp expect actual
+'
+
 # tests for pull --set-upstream
 
 test_expect_success 'setup bare parent pull' '
@@ -178,4 +189,15 @@ test_expect_success 'pull --set-upstream with valid URL and branch sets branch'
 	check_config_missing other2
 '
 
+test_expect_success 'pull --set-upstream with a detached HEAD' '
+	git checkout HEAD^0 &&
+	test_when_finished "git checkout -" &&
+	cat >expect <<-\EOF &&
+	warning: could not set upstream of HEAD to '"'"'main'"'"' from '"'"'upstream'"'"' when it does not point to any branch.
+	EOF
+	git pull --no-rebase --set-upstream upstream main 2>actual.raw &&
+	grep ^warning: actual.raw >actual &&
+	test_cmp expect actual
+'
+
 test_done
