mingw: handle `subst`-ed "DOS drives"
Over a decade ago, in 25fe217b86c (Windows: Treat Windows style path
names., 2008-03-05), Git was taught to handle absolute Windows paths,
i.e. paths that start with a drive letter and a colon.
Unbeknownst to us, while drive letters of physical drives are limited to
letters of the English alphabet, there is a way to assign virtual drive
letters to arbitrary directories, via the `subst` command, which is
_not_ limited to English letters.
It is therefore possible to have absolute Windows paths of the form
`1:\what\the\hex.txt`. Even "better": pretty much arbitrary Unicode
letters can also be used, e.g. `ä:\tschibät.sch`.
While it can be sensibly argued that users who set up such funny drive
letters really seek adverse consequences, the Windows Operating System
is known to be a platform where many users are at the mercy of
administrators who have their very own idea of what constitutes a
reasonable setup.
Therefore, let's just make sure that such funny paths are still
considered absolute paths by Git, on Windows.
In addition to Unicode characters, pretty much any character is a valid
drive letter, as far as `subst` is concerned, even `:` and `"` or even a
space character. While it is probably the opposite of smart to use them,
let's safeguard `is_dos_drive_prefix()` against all of them.
Note: `[::1]:repo` is a valid URL, but not a valid path on Windows.
As `[` is now considered a valid drive letter, we need to be very
careful to avoid misinterpreting such a string as valid local path in
`url_is_local_not_ssh()`. To do that, we use the just-introduced
function `is_valid_path()` (which will label the string as invalid file
name because of the colon characters).
This fixes CVE-2019-1351.
Reported-by: Nicolas Joly <Nicolas.Joly@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
diff --git a/compat/mingw.c b/compat/mingw.c
index 3aea269..27d6f4a 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -1986,6 +1986,30 @@
return -1;
}
+int mingw_has_dos_drive_prefix(const char *path)
+{
+ int i;
+
+ /*
+ * Does it start with an ASCII letter (i.e. highest bit not set),
+ * followed by a colon?
+ */
+ if (!(0x80 & (unsigned char)*path))
+ return *path && path[1] == ':' ? 2 : 0;
+
+ /*
+ * While drive letters must be letters of the English alphabet, it is
+ * possible to assign virtually _any_ Unicode character via `subst` as
+ * a drive letter to "virtual drives". Even `1`, or `ä`. Or fun stuff
+ * like this:
+ *
+ * subst ֍: %USERPROFILE%\Desktop
+ */
+ for (i = 1; i < 4 && (0x80 & (unsigned char)path[i]); i++)
+ ; /* skip first UTF-8 character */
+ return path[i] == ':' ? i + 1 : 0;
+}
+
int mingw_skip_dos_drive_prefix(char **path)
{
int ret = has_dos_drive_prefix(*path);
diff --git a/compat/mingw.h b/compat/mingw.h
index 7482f19..1706466 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -394,8 +394,8 @@
* git specific compatibility
*/
-#define has_dos_drive_prefix(path) \
- (isalpha(*(path)) && (path)[1] == ':' ? 2 : 0)
+int mingw_has_dos_drive_prefix(const char *path);
+#define has_dos_drive_prefix mingw_has_dos_drive_prefix
int mingw_skip_dos_drive_prefix(char **path);
#define skip_dos_drive_prefix mingw_skip_dos_drive_prefix
static inline int mingw_is_dir_sep(int c)
diff --git a/connect.c b/connect.c
index 49b28b8..a053cc2 100644
--- a/connect.c
+++ b/connect.c
@@ -264,7 +264,7 @@
const char *colon = strchr(url, ':');
const char *slash = strchr(url, '/');
return !colon || (slash && slash < colon) ||
- has_dos_drive_prefix(url);
+ (has_dos_drive_prefix(url) && is_valid_path(url));
}
static const char *prot_name(enum protocol protocol)
diff --git a/t/t0060-path-utils.sh b/t/t0060-path-utils.sh
index f7e2529..40db3e1 100755
--- a/t/t0060-path-utils.sh
+++ b/t/t0060-path-utils.sh
@@ -165,6 +165,15 @@
test_must_fail test-path-utils absolute_path ""
'
+test_expect_success MINGW '<drive-letter>:\\abc is an absolute path' '
+ for letter in : \" C Z 1 ä
+ do
+ path=$letter:\\abc &&
+ absolute="$(test-path-utils absolute_path "$path")" &&
+ test "$path" = "$absolute" || return 1
+ done
+'
+
test_expect_success 'real path rejects the empty string' '
test_must_fail test-path-utils real_path ""
'
