merge-ort: fix calling merge_finalize() with no intermediate merge

From: Elijah Newren <[email protected]>

While at it, ensure the FREE_AND_NULL() in the function does something useful with the nulling aspect, namely sets result->priv to NULL rather than a mere temporary.

void merge_finalize(struct merge_options *opt,

merge-ort.c +0 -2

 		    struct merge_result *result)
 {
-	struct merge_options_internal *opti = result->priv;
-

Quoted 5 lines · Elijah Newren via GitGitGadget

From: Elijah Newren <[email protected]>

While at it, ensure the FREE_AND_NULL() in the function does something useful with the nulling aspect, namely sets result->priv to NULL rather than a mere temporary.

Good call. It also makes the code look better.

Perhaps this would be better as

	if (result->priv) {
		clear_or_reinit_internal_opts(result->priv, 0);
		FREE_AND_NULL(result->priv);
	}

to avoid an accidental addition of code to the end of this method that doesn't depend on result->priv?

Quoted 5 lines · Elijah Newren via GitGitGadget

From: Elijah Newren <[email protected]>

While at it, ensure the FREE_AND_NULL() in the function does something useful with the nulling aspect, namely sets result->priv to NULL rather than a mere temporary.

Good call. It also makes the code look better.

Quoted 5 lines

void merge_finalize(struct merge_options *opt,
struct merge_result *result)
{

merge-ort.c +0 -2

-     struct merge_options_internal *opti = result->priv;
-

merge-ort.c void merge_switch_to_result(struct merge_options *opt, · line 4728

Quoted 10 lines

merge-ort.c +4 -2

      if (opt->renormalize)
              git_attr_set_direction(GIT_ATTR_CHECKIN);
      assert(opt->priv == NULL);
 
-     clear_or_reinit_internal_opts(opti, 0);
-     FREE_AND_NULL(opti);
+     if (!result->priv)
+             return;
+     clear_or_reinit_internal_opts(result->priv, 0);
+     FREE_AND_NULL(result->priv);

Perhaps this would be better as

        if (result->priv) {
                clear_or_reinit_internal_opts(result->priv, 0);
                FREE_AND_NULL(result->priv);
        }

to avoid an accidental addition of code to the end of this method that doesn't depend on result->priv?

From: Elijah Newren <[email protected]>

If some code sets up the data structures for a merge, but then never actually performs one before calling merge_finalize(), then merge_finalize() wouldn't notice that result->priv was NULL and return early, resulting in following that NULL pointer and getting a segfault. There is currently no code in the git codebase that does this, but this issue was found during testing of some proposed patches that had the following structure:

    struct merge_options merge_opt;
    struct merge_result result;

    init_merge_options(&merge_opt, the_repository);
    memset(&result, 0, sizeof(result));

    <do N merges, for some value of N>

    merge_finalize(&merge_opt, &result);

where some flags could cause the code to have N=0, i.e. doing no merges. Add a check for result->priv being NULL and return early to avoid a segfault in these kinds of cases.

While at it, ensure the FREE_AND_NULL() in the function does something useful with the nulling aspect, namely sets result->priv to NULL rather than a mere temporary.

Reported-by Derrick Stolee <[email protected]>

Signed-off-by Elijah Newren <[email protected]>

---
merge-ort: fix calling merge_finalize() with no intermediate merge

See
https://lore.kernel.org/git/CABPp-BHCdjOutYqdMO1NbYKNA0BgkXRgwUEKK=MX0kXM-5G_DQ@mail.gmail.com/

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1518%2Fnewren%2Ffix-merge-finalize-with-no-merge-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1518/newren/fix-merge-finalize-with-no-merge-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1518

 merge-ort.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

merge-ort.c +4 -4

index 5bf64354d16..cba3662e497 100644
@@ -4718,14 +4718,14 @@ void merge_switch_to_result(struct merge_options *opt,
 void merge_finalize(struct merge_options *opt,
 		    struct merge_result *result)
 {
-	struct merge_options_internal *opti = result->priv;
-
 	if (opt->renormalize)
 		git_attr_set_direction(GIT_ATTR_CHECKIN);
 	assert(opt->priv == NULL);
 
-	clear_or_reinit_internal_opts(opti, 0);
-	FREE_AND_NULL(opti);
+	if (!result->priv)
+		return;
+	clear_or_reinit_internal_opts(result->priv, 0);
+	FREE_AND_NULL(result->priv);
 }
 
 /*** Function Grouping: helper functions for merge_incore_*() ***/

base-commit: 667fcf4e15379790f0b609d6a83d578e69f20301

merge-ort: fix calling merge_finalize() with no intermediate merge

Changes since v1:

* Moved code into an if-block instead of returning early, as suggested by Stolee.