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 3aea26982d6a04bcdd642fe328fd2cde28ba1c0b..27d6f4ac30bc2fc563e69e7bae8fcb153e0461a6 100644 (file)
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -1986,6 +1986,30 @@ pid_t waitpid(pid_t pid, int *status, int options)
        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 7482f196afdd2741658c2bd28a2e7eb0d740d3dd..17064665d9400ce607abbc3c817b9fc57e4dbdca 100644 (file)
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -394,8 +394,8 @@ HANDLE winansi_get_osfhandle(int fd);
  * 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 49b28b83be2717027ac33570b1041604db5a062d..a053cc256d42b6a15375de7d0ce74f18833c1821 100644 (file)
--- a/connect.c
+++ b/connect.c
@@ -264,7 +264,7 @@ int url_is_local_not_ssh(const char *url)
        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 f7e2529bffc143d15af01d6700fa4953e7d2d3b2..40db3e1e1adad57721087ee69af35224aa6eaad4 100755 (executable)
--- a/t/t0060-path-utils.sh
+++ b/t/t0060-path-utils.sh
@@ -165,6 +165,15 @@ test_expect_success 'absolute path rejects the empty string' '
        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 ""
 '