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mingw: disallow backslash characters in tree objects' file names

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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>
This commit is contained in:
Johannes Schindelin
2019-09-12 14:54:05 +02:00
parent 0060fd1511
commit e1d911dd4c
4 changed files with 13 additions and 3 deletions
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6
tree-walk.c
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@@ -41,6 +41,12 @@ static int decode_tree_entry(struct tree_desc *desc, const char *buf, unsigned l
strbuf_addstr(err, _("empty filename in tree entry"));
return -1;
}
#ifdef GIT_WINDOWS_NATIVE
if (protect_ntfs && strchr(path, '\\')) {
strbuf_addf(err, _("filename in tree entry contains backslash: '%s'"), path);
return -1;
}
#endif
len = strlen(path) + 1;
/* Initialize the descriptor entry */