[PATCH v7] 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. However, cascade_pseudo_merges_1() uses roots_bitmap as a mutable reference without taking ownership of it. As a result, if cascade_pseudo_merges_1() succeeds, roots_bitmap is leaked. 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 roots_bitmap that contains at least one pseudo merge. So that we can use pseudo merge bitmap when we compute roots reachable bitmap. Here we create two commits: first A then B. Add A to the pseudo-merge 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-v7
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1977/brandb97/remove-check-before-bitmap-free-v7
Pull-Request: https://github.com/git/git/pull/1977

Range-diff vs v6:

 1:  43cdce190dc ! 1:  74c41eccfb0 pack-bitmap: remove checks before bitmap_free
     @@ Commit message
          pack-bitmap: remove checks before bitmap_free
      
          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() succeeds, roots_bitmap leaks.
     +    if cascade_pseudo_merges_1() fails. However, cascade_pseudo_merges_1()
     +    uses roots_bitmap as a mutable reference without taking ownership of it.
     +    As a result, if cascade_pseudo_merges_1() succeeds, roots_bitmap is leaked.
          And this leak currently lacks a dedicated test to detect it.
      
          To fix this leak, remove if cascade_pseudo_merges_1() succeed check and

 pack-bitmap.c                   |  4 ++--
 t/t5333-pseudo-merge-bitmaps.sh | 17 +++++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)