[PATCH v5 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

Update since Patch series V4

 * Squashed in Junio's patch to handle non-master named branches
 * Explicitly use test_unconfig

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 | 51 +++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+), 3 deletions(-)

base-commit: 898f80736c75878acc02dc55672317fcc0e0a5a6
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-820%2Fnipunn1313%2Fnk%2Fpush-refspec-segfault-v5
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-820/nipunn1313/nk/push-refspec-segfault-v5
Pull-Request: https://github.com/gitgitgadget/git/pull/820

Range-diff vs v4:

 1:  e59ff29bdef ! 1:  48c79dc3d84 negative-refspec: fix segfault on : refspec
     @@ t/t5582-fetch-negative-refspec.sh: test_expect_success "fetch --prune with negat
       '
       
      +test_expect_success "push with matching : and negative refspec" '
     -+	test_config -C two remote.one.push : &&
     -+	# Fails to push master w/ tip behind counterpart
     ++	# Manually handle cleanup, since test_config is not
     ++	# prepared to take arbitrary options like --add
     ++	test_when_finished "test_unconfig -C two remote.one.push" &&
     ++
     ++	# For convenience, we use "master" to refer to the name of
     ++	# the branch created by default in the following.
     ++	#
     ++	# Repositories two and one have branches other than "master"
     ++	# but they have no overlap---"master" is the only one that
     ++	# is shared between them.  And the master branch at two is
     ++	# behind the master branch at one by one commit.
     ++	git -C two config --add remote.one.push : &&
     ++
     ++	# A matching push tries to update master, fails due to non-ff
      +	test_must_fail git -C two push one &&
      +
     ++	# "master" may actually not be "master"---find it out.
     ++	current=$(git symbolic-ref HEAD) &&
     ++
      +	# If master is in negative refspec, then the command will not attempt
      +	# to push and succeed.
     -+	# We do not need test_config here as we are updating remote.one.push
     -+	# again. The teardown of the first test_config will do --unset-all
     -+	git -C two config --add remote.one.push ^refs/heads/master &&
     -+	git -C two push one
     ++	git -C two config --add remote.one.push "^$current" &&
     ++
     ++	# With "master" excluded, this push is a no-op.  Nothing gets
     ++	# pushed and it succeeds.
     ++	git -C two push -v one
      +'
      +
      +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_when_finished "test_unconfig -C two remote.one.push" &&
     ++
     ++	# The same set-up as above, whose side-effect was a no-op.
     ++	git -C two config --add remote.one.push +: &&
     ++
     ++	# The push refuses to update the "master" branch that is checked
     ++	# out in the "one" repository, even when it is forced with +:
      +	test_must_fail git -C two push one &&
      +
     ++	# "master" may actually not be "master"---find it out.
     ++	current=$(git symbolic-ref HEAD) &&
     ++
      +	# If master is in negative refspec, then the command will not attempt
      +	# to push and succeed
     -+	git -C two config --add remote.one.push ^refs/heads/master &&
     -+	git -C two push one
     ++	git -C two config --add remote.one.push "^$current" &&
     ++
     ++	# With "master" excluded, this push is a no-op.  Nothing gets
     ++	# pushed and it succeeds.
     ++	git -C two push -v one
      +'
      +
       test_done
 2:  20575407cc0 = 2:  1f9af0e991c negative-refspec: improve comment on query_matches_negative_refspec