rebase -i: stop overwriting ORIG_HEAD buffer

After rebasing, ORIG_HEAD is supposed to point to the old HEAD of the
rebased branch.  The code used find_unique_abbrev() to obtain the
object name of the old HEAD and wrote to both
.git/rebase-merge/orig-head (used by `rebase --abort` to go back to
the previous state) and to ORIG_HEAD.  The buffer find_unique_abbrev()
gives back is volatile, unfortunately, and was overwritten after the
former file is written but before ORIG_FILE is written, leaving an
incorrect object name in it.

Avoid relying on the volatile buffer of find_unique_abbrev(), and
instead supply our own buffer to keep the object name.

I think that all of the users of head_hash should actually be using
opts->orig_head instead as passing a string rather than a struct
object_id around is a hang over from the scripted implementation. This
patch just fixes the immediate bug and adds a regression test based on
Caspar's reproduction example[1]. The users will be converted to use
struct object_id and head_hash removed in the next few commits.

[1] https://lore.kernel.org/git/CAFzd1+7PDg2PZgKw7U0kdepdYuoML9wSN4kofmB_-8NHrbbrHg@mail.gmail.com

Reported-by: Caspar Duregger <herr.kaste@gmail.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/rebase.c b/builtin/rebase.c
index eeca53382f793356e5f4a0114de062fb3926e236..cd101b2559caecb25da84741366bee01356e22f1 100644 (file)
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -270,15 +270,15 @@ static int edit_todo_file(unsigned flags)
 }
 
 static int get_revision_ranges(struct commit *upstream, struct commit *onto,
-                              struct object_id *orig_head, const char **head_hash,
+                              struct object_id *orig_head, char *head_hash,
                               char **revisions, char **shortrevisions)
 {
        struct commit *base_rev = upstream ? upstream : onto;
        const char *shorthead;
 
-       *head_hash = find_unique_abbrev(orig_head, GIT_MAX_HEXSZ);
+       find_unique_abbrev_r(head_hash, orig_head, GIT_MAX_HEXSZ);
        *revisions = xstrfmt("%s...%s", oid_to_hex(&base_rev->object.oid),
-                                                  *head_hash);
+                                                  head_hash);
 
        shorthead = find_unique_abbrev(orig_head, DEFAULT_ABBREV);
 
@@ -327,7 +327,7 @@ static void split_exec_commands(const char *cmd, struct string_list *commands)
 static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
 {
        int ret;
-       const char *head_hash = NULL;
+       char head_hash[GIT_MAX_HEXSZ];
        char *revisions = NULL, *shortrevisions = NULL;
        struct strvec make_script_args = STRVEC_INIT;
        struct todo_list todo_list = TODO_LIST_INIT;
@@ -335,7 +335,7 @@ static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
        struct string_list commands = STRING_LIST_INIT_DUP;
 
        if (get_revision_ranges(opts->upstream, opts->onto, &opts->orig_head,
-                               &head_hash, &revisions, &shortrevisions))
+                               head_hash, &revisions, &shortrevisions))
                return -1;
 
        if (init_basic_state(&replay,

diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 07a1617351dad9729b1b440422fced90a01cc25f..1e56696e4ff2aac546a473e9a8e5391a5b4fef16 100755 (executable)
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1797,6 +1797,17 @@ test_expect_success 'todo has correct onto hash' '
        test_i18ngrep "^# Rebase ..* onto $onto" actual
 '
 
+test_expect_success 'ORIG_HEAD is updated correctly' '
+       test_when_finished "git checkout master && git branch -D test-orig-head" &&
+       git checkout -b test-orig-head A &&
+       git commit --allow-empty -m A1 &&
+       git commit --allow-empty -m A2 &&
+       git commit --allow-empty -m A3 &&
+       git commit --allow-empty -m A4 &&
+       git rebase master &&
+       test_cmp_rev ORIG_HEAD test-orig-head@{1}
+'
+
 # This must be the last test in this file
 test_expect_success '$EDITOR and friends are unchanged' '
        test_editor_unchanged