[PATCH v4 0/2] negative-refspec: fix segfault on : refspec

If remote.origin.push was set to ":", git segfaults during a push operation, due to bad parsing logic in query_matches_negative_refspec. Per bisect, the bug was introduced in: c0192df630 (refspec: add support for negative refspecs, 2020-09-30)

We found this issue when rolling out git 2.29 at Dropbox - as several folks had "push = :" in their configuration. I based my diff off the master branch, but also confirmed that it patches cleanly onto maint - if the maintainers would like to also fix the segfault on 2.29

Update since Patch series V1:

 * Handled matching refspec explicitly
 * Added testing for "+:" case
 * Added comment explaining how the two loops work together

Update since Patch series V2

 * style suggestion in remote.c
 * Use test_config
 * Add test for a case with a matching refspec + negative refspec
 * Fix test_config to work with --add
 * Updated commit message to describe what git is told to do instead of
   segfaulting

Update since Patch series V3

 * Removed commit modifying test_config
 * Remove segfault-related comments in test
 * Consolidate the three tests to two tests (1st and 3rd test overlapped in
   functionality)
 * Base the patch series on the maint branch - since the bug affects 2.29.2

Appreciate the reviews from Junio and Eric! Happy Holidays!

Nipunn Koorapati (2):
  negative-refspec: fix segfault on : refspec
  negative-refspec: improve comment on query_matches_negative_refspec

 remote.c                          | 16 +++++++++++++---
 t/t5582-fetch-negative-refspec.sh | 24 ++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 3 deletions(-)

base-commit: 898f80736c75878acc02dc55672317fcc0e0a5a6
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-820%2Fnipunn1313%2Fnk%2Fpush-refspec-segfault-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-820/nipunn1313/nk/push-refspec-segfault-v4
Pull-Request: https://github.com/gitgitgadget/git/pull/820

Range-diff vs v3:

 1:  733c674bd19 < -:  ----------- test-lib-functions: handle --add in test_config
 2:  20cff2f5c59 ! 1:  e59ff29bdef negative-refspec: fix segfault on : refspec
     @@ Commit message
          (refspec: add support for negative refspecs, 2020-09-30) looks at
          refspec->src assuming it is never NULL, however when
          remote.origin.push is set to ":", then refspec->src is NULL,
     -    causing a segfault within strcmp
     +    causing a segfault within strcmp.
      
          Tell git to handle matching refspec by adding the needle to the
          set of positively matched refspecs, since matching ":" refspecs
          match anything as src.
      
     -    Added testing for matching refspec pushes fetch-negative-refspec
     -    both individually and in combination with a negative refspec
     +    Add test for matching refspec pushes fetch-negative-refspec
     +    both individually and in combination with a negative refspec.
      
          Signed-off-by: Nipunn Koorapati <nipunn@dropbox.com>
      
     @@ t/t5582-fetch-negative-refspec.sh: test_expect_success "fetch --prune with negat
       	)
       '
       
     -+test_expect_success "push with matching ':' refspec" '
     ++test_expect_success "push with matching : and negative refspec" '
      +	test_config -C two remote.one.push : &&
     -+	# Fails w/ tip behind counterpart - but should not segfault
     -+	test_must_fail git -C two push one
     -+'
     ++	# Fails to push master w/ tip behind counterpart
     ++	test_must_fail git -C two push one &&
      +
     -+test_expect_success "push with matching '+:' refspec" '
     -+	test_config -C two remote.one.push +: &&
     -+	# Fails w/ tip behind counterpart - but should not segfault
     -+	test_must_fail git -C two push one
     ++	# If master is in negative refspec, then the command will not attempt
     ++	# to push and succeed.
     ++	# We do not need test_config here as we are updating remote.one.push
     ++	# again. The teardown of the first test_config will do --unset-all
     ++	git -C two config --add remote.one.push ^refs/heads/master &&
     ++	git -C two push one
      +'
      +
     -+test_expect_success "push with matching and negative refspec" '
     -+	test_config -C two --add remote.one.push : &&
     ++test_expect_success "push with matching +: and negative refspec" '
     ++	test_config -C two remote.one.push +: &&
      +	# Fails to push master w/ tip behind counterpart
      +	test_must_fail git -C two push one &&
      +
     -+	# If master is in negative refspec, then the command will succeed
     -+	test_config -C two --add remote.one.push ^refs/heads/master &&
     ++	# If master is in negative refspec, then the command will not attempt
     ++	# to push and succeed
     ++	git -C two config --add remote.one.push ^refs/heads/master &&
      +	git -C two push one
      +'
      +
 3:  0fd4e9f7459 = 2:  20575407cc0 negative-refspec: improve comment on query_matches_negative_refspec