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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/read-cache.c b/read-cache.c
index 5a907af2fb52f53d2e533edeec5f9ed470f8ba31..b6c13bc04e17314878a56b9a333e86db0ce2d3a6 100644 (file)
--- a/read-cache.c
+++ b/read-cache.c
@@ -985,7 +985,7 @@ inside:
                                }
                        }
                        if (protect_ntfs) {
-#ifdef GIT_WINDOWS_NATIVE
+#if defined GIT_WINDOWS_NATIVE || defined __CYGWIN__
                                if (c == '\\')
                                        return 0;
 #endif

diff --git a/t/t7415-submodule-names.sh b/t/t7415-submodule-names.sh
index f70368bc2e9d42cc578ed4b46edac324bd1dddf1..6bf098a6bea3080aa9019728fe790b2a91f146e2 100755 (executable)
--- 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' '

diff --git a/t/test-lib.sh b/t/test-lib.sh
index d3f6af6a65451cdd7868e5dc355b44fed49a0670..e84b8c87f9db1b9b1e071d92d2c6fcdd8c511ef3 100644 (file)
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1457,6 +1457,7 @@ 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*)
@@ -1465,6 +1466,7 @@ case $uname_s in
        test_set_prereq CYGWIN
        test_set_prereq SED_STRIPS_CR
        test_set_prereq GREP_STRIPS_CR
+       test_set_prereq WINDOWS
        ;;
 *)
        test_set_prereq POSIXPERM