[PATCH v4] pack-bitmap: remove checks before bitmap_free

From: Lidong Yan <502024330056@smail.nju.edu.cn>

In pack-bitmap.c:find_boundary_objects(), the roots_bitmap is only freed if cascade_pseudo_merges_1() fails. Since cascade_pseudo_merges_1() only use roots_bitmap as a mutable reference but not takes roots_bitmap's ownership. Once cascade_pseudo_merges_1 succeed(), roots_bitmap leaks. And this leak currently lacks a dedicated test to detect it.

To fix this leak, remove if cascade_pseudo_merges_1() succeed check and always calling bitmap_free(roots_bitmap);

To trigger this leak, we need a pseudo-merge whose size is equal to or smaller than roots_bitmap (which corresponds to the set of "haves" commits in prepare_bitmap_walk()). To do this, we can create two commits: A and B. Add A to the pseudo-merge list and perform a traversal over the range A..B. In this scenario, the "haves" set will be {A}, and cascade_pseudo_merges_1() will succeed, thereby exposing the leak due to the missing roots_bitmap cleanup.

Signed-off-by: Lidong Yan <502024330056@smail.nju.edu.cn>
---
    pack-bitmap: remove checks before bitmap_free
    
    In pack-bitmap.c:find_boundary_objects, remove cascade success check and
    always free roots_bitmap afterward to make static analysis tool works
    better.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1977%2Fbrandb97%2Fremove-check-before-bitmap-free-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1977/brandb97/remove-check-before-bitmap-free-v4
Pull-Request: https://github.com/git/git/pull/1977

Range-diff vs v3:

 1:  151a7f5dc70 ! 1:  fa443065436 pack-bitmap: remove checks before bitmap_free
     @@ t/t5333-pseudo-merge-bitmaps.sh: test_expect_success 'pseudo-merge closure' '
      +		git config bitmapPseudoMerge.test.pattern refs/ &&
      +		git config bitmapPseudoMerge.test.threshold now &&
      +		git config bitmapPseudoMerge.test.stableThreshold now &&
     -+		GIT_TEST_PACK_USE_BITMAP_BOUNDARY_TRAVERSAL=1 &&
      +
      +		test_commit A &&
      +		git repack -adb &&
      +		test_commit B &&
      +
      +		echo '1' >expect &&
     -+		git rev-list --count --use-bitmap-index HEAD~1..HEAD >actual &&
     ++		GIT_TEST_PACK_USE_BITMAP_BOUNDARY_TRAVERSAL=1 \
     ++			git rev-list --count --use-bitmap-index HEAD~1..HEAD >actual &&
      +		test_cmp expect actual
      +	)
      +'

 pack-bitmap.c                   |  4 ++--
 t/t5333-pseudo-merge-bitmaps.sh | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)