mingw: disallow backslash characters in tree objects' file names
The backslash character is not a valid part of a file name on Windows.
Hence it is dangerous to allow writing files that were unpacked from
tree objects, when the stored file name contains a backslash character:
it will be misinterpreted as directory separator.
This not only causes ambiguity when a tree contains a blob `a\b` and a
tree `a` that contains a blob `b`, but it also can be used as part of an
attack vector to side-step the careful protections against writing into
the `.git/` directory during a clone of a maliciously-crafted
repository.
Let's prevent that, addressing CVE-2019-1354.
Note: we guard against backslash characters in tree objects' file names
_only_ on Windows (because on other platforms, even on those where NTFS
volumes can be mounted, the backslash character is _not_ a directory
separator), and _only_ when `core.protectNTFS = true` (because users
might need to generate tree objects for other platforms, of course
without touching the worktree, e.g. using `git update-index
--cacheinfo`).
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
diff --git a/t/t9350-fast-export.sh b/t/t9350-fast-export.sh
index 866ddf6..e606207 100755
--- a/t/t9350-fast-export.sh
+++ b/t/t9350-fast-export.sh
@@ -421,6 +421,7 @@
test_expect_success 'fast-export quotes pathnames' '
git init crazy-paths &&
+ test_config -C crazy-paths core.protectNTFS false &&
(cd crazy-paths &&
blob=$(echo foo | git hash-object -w --stdin) &&
git update-index --add \
