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

Fix a segfault in the --set-upstream option added in
24bc1a12926 (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 8efb8899cfe (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
6183d826ba6 (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 8efb8899cfe, 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 24bc1a12926 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 7d0daf3f12f (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
index f7abbc31ff1414d46ff87cbace917b96181dac13..7f3d2fdc9cecfbc7aacccf7f3ca92c07fca2aa84 100644 (file)
--- 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
index 9c12c0f8c321def9e39d0887d463b5d227d3157d..48050162c27440dab8a0dbc5cd19a2781bee2d37 100755 (executable)
--- 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