Re: [PATCH] cygwin: disallow backslashes in file names

> The backslash character is not a valid part of a file name on Windows.
> If, in Windows, Git attempts to write a file that has a backslash
> character in the filename, it will be incorrectly interpreted as a
> directory separator.
>
> This caused CVE-2019-1354 in MinGW, as this behaviour can be manipulated
> to cause the checkout to write to files it ought not write to, such as
> adding code to the .git/hooks directory.  This was fixed by e1d911dd4c
> (mingw: disallow backslash characters in tree objects' file names,
> 2019-09-12).  However, the vulnerability also exists in Cygwin: while
> Cygwin mostly provides a POSIX-like path system, it will still interpret
> a backslash as a directory separator.
>
> To avoid this vulnerability, CVE-2021-29468, extend the previous fix to
> also apply to Cygwin.
>
> Similarly, extend the test case added by the previous version of the
> commit.  The test suite doesn't have an easy way to say "run this test
> if in MinGW or Cygwin", so add a new test prerequisite that covers both.
>
> As well as checking behaviour in the presence of paths containing
> backslashes, the existing test also checks behaviour in the presence of
> paths that differ only by the presence of a trailing ".".  MinGW follows
> normal Windows application behaviour and treats them as the same path,
> but Cygwin more closely emulates *nix systems (at the expense of
> compatibility with native Windows applications) and will create and
> distinguish between such paths.  Gate the relevant bit of that test
> accordingly.
>
> Reported-by: RyotaK <security@ryotak.me>
> Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> Signed-off-by: Adam Dinwoodie <adam@dinwoodie.org>
> ---

>  read-cache.c               |  2 +-
>  t/test-lib.sh              |  2 ++
>  t/t7415-submodule-names.sh | 13 ++++++++-----
>  3 files changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/read-cache.c b/read-cache.c
> index 5a907af2fb..b6c13bc04e 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -985,7 +985,7 @@ int verify_path(const char *path, unsigned mode)
>  				}
>  			}
>  			if (protect_ntfs) {
> -#ifdef GIT_WINDOWS_NATIVE
> +#if defined GIT_WINDOWS_NATIVE || defined __CYGWIN__
>  				if (c == '\\')
>  					return 0;
>  #endif
> diff --git a/t/test-lib.sh b/t/test-lib.sh
> index d3f6af6a65..e84b8c87f9 100644
> --- a/t/test-lib.sh
> +++ b/t/test-lib.sh
> @@ -1457,14 +1457,16 @@ case $uname_s in
>  	test_set_prereq NATIVE_CRLF
>  	test_set_prereq SED_STRIPS_CR
>  	test_set_prereq GREP_STRIPS_CR
> +	test_set_prereq WINDOWS
>  	GIT_TEST_CMP=mingw_test_cmp
>  	;;
>  *CYGWIN*)
>  	test_set_prereq POSIXPERM
>  	test_set_prereq EXECKEEPSPID
>  	test_set_prereq CYGWIN
>  	test_set_prereq SED_STRIPS_CR
>  	test_set_prereq GREP_STRIPS_CR
> +	test_set_prereq WINDOWS
>  	;;
>  *)
>  	test_set_prereq POSIXPERM
> diff --git a/t/t7415-submodule-names.sh b/t/t7415-submodule-names.sh
> index f70368bc2e..6bf098a6be 100755
> --- a/t/t7415-submodule-names.sh
> +++ b/t/t7415-submodule-names.sh
> @@ -191,7 +191,7 @@ test_expect_success 'fsck detects corrupt .gitmodules' '
>  	)
>  '
>  
> -test_expect_success MINGW 'prevent git~1 squatting on Windows' '
> +test_expect_success WINDOWS 'prevent git~1 squatting on Windows' '
>  	git init squatting &&
>  	(
>  		cd squatting &&
> @@ -219,10 +219,13 @@ test_expect_success MINGW 'prevent git~1 squatting on Windows' '
>  		test_tick &&
>  		git -c core.protectNTFS=false commit -m "module"
>  	) &&
> -	test_must_fail git -c core.protectNTFS=false \
> -		clone --recurse-submodules squatting squatting-clone 2>err &&
> -	test_i18ngrep -e "directory not empty" -e "not an empty directory" err &&
> -	! grep gitdir squatting-clone/d/a/git~2
> +	if test_have_prereq MINGW
> +	then
> +		test_must_fail git -c core.protectNTFS=false \
> +			clone --recurse-submodules squatting squatting-clone 2>err &&
> +		test_i18ngrep -e "directory not empty" -e "not an empty directory" err &&
> +		! grep gitdir squatting-clone/d/a/git~2
> +	fi
>  '
>  
>  test_expect_success 'git dirs of sibling submodules must not be nested' '