Merge branch 'jv/merge-nothing-into-void'

"git merge FETCH_HEAD" dereferenced NULL pointer when merging
nothing into an unborn history (which is arguably unusual usage,
which perhaps was the reason why nobody noticed it).

* jv/merge-nothing-into-void:
merge: fix NULL pointer dereference when merging nothing into void

diff --git a/builtin/merge.c b/builtin/merge.c
index c8154aaf6a5afa87ab42d3db632798698a9f2b1d..30b7bd54fab38beed4ef1b48a4aacda0fb018987 100644 (file)
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -1258,12 +1258,12 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
                        builtin_merge_options);
 
        if (!head_commit) {
-               struct commit *remote_head;
                /*
                 * If the merged head is a valid one there is no reason
                 * to forbid "git merge" into a branch yet to be born.
                 * We do the same for "git pull".
                 */
+               unsigned char *remote_head_sha1;
                if (squash)
                        die(_("Squash commit into empty head not supported yet"));
                if (fast_forward == FF_NO)
@@ -1271,13 +1271,13 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
                            "an empty head"));
                remoteheads = collect_parents(head_commit, &head_subsumed,
                                              argc, argv, NULL);
-               remote_head = remoteheads->item;
-               if (!remote_head)
+               if (!remoteheads)
                        die(_("%s - not something we can merge"), argv[0]);
                if (remoteheads->next)
                        die(_("Can merge only exactly one commit into empty head"));
-               read_empty(remote_head->object.oid.hash, 0);
-               update_ref("initial pull", "HEAD", remote_head->object.oid.hash,
+               remote_head_sha1 = remoteheads->item->object.oid.hash;
+               read_empty(remote_head_sha1, 0);
+               update_ref("initial pull", "HEAD", remote_head_sha1,
                           NULL, 0, UPDATE_REFS_DIE_ON_ERR);
                goto done;
        }

diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh
index dc9f142f537e53de34156a9c7fddf3be49a0e219..85248a14b61d68b61932d595eb0fa8fcaa8506b1 100755 (executable)
--- a/t/t7600-merge.sh
+++ b/t/t7600-merge.sh
@@ -753,4 +753,14 @@ test_expect_success 'merge detects mod-256 conflicts (resolve)' '
        test_must_fail git merge -s resolve master
 '
 
+test_expect_success 'merge nothing into void' '
+       git init void &&
+       (
+               cd void &&
+               git remote add up .. &&
+               git fetch up &&
+               test_must_fail git merge FETCH_HEAD
+       )
+'
+
 test_done