get_relocated_path() did not have error handling for PathCchSkipRoot()
because a path given to get_relocated_path() was expected to be a valid
path containing a drive letter or UNC server/share path elements on
Windows, but sometimes it turned out otherwise.

The paths passed to get_relocated_path() are defined by macros generated
by Meson. Meson in turn uses a prefix given by the configure script to
generate them. For Windows, the script passes /qemu as a prefix to
Meson by default.

As documented in docs/about/build-platforms.rst, typically MSYS2 is used
for the build system, but it is also possible to use Linux as well. When
MSYS2 is used, its Bash variant recognizes /qemu as a MSYS2 path, and
converts it to a Windows path, adding the MSYS2 prefix including a drive
letter or UNC server/share path elements. Such a conversion does not
happen on a shell on Linux however, and /qemu will be passed as is in
the case.

Implement a proper error handling of PathCchSkipRoot() in
get_relocated_path() so that it can handle a path without a drive letter
or UNC server/share path elements.

Reported-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
V1 -> V2: Compare against S_OK for clarity (Philippe Mathieu-Daudé)

 util/cutils.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/util/cutils.c b/util/cutils.c
index 25373198ad..770d6e023c 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -1155,17 +1155,21 @@ char *get_relocated_path(const char *dir)
     g_string_append(result, "/qemu-bundle");
     if (access(result->str, R_OK) == 0) {
 #ifdef G_OS_WIN32
-        size_t size = mbsrtowcs(NULL, &dir, 0, &(mbstate_t){0}) + 1;
+        const char *src = dir;
+        size_t size = mbsrtowcs(NULL, &src, 0, &(mbstate_t){0}) + 1;
         PWSTR wdir = g_new(WCHAR, size);
-        mbsrtowcs(wdir, &dir, size, &(mbstate_t){0});
+        mbsrtowcs(wdir, &src, size, &(mbstate_t){0});
 
         PCWSTR wdir_skipped_root;
-        PathCchSkipRoot(wdir, &wdir_skipped_root);
+        if (PathCchSkipRoot(wdir, &wdir_skipped_root) == S_OK) {
+            size = wcsrtombs(NULL, &wdir_skipped_root, 0, &(mbstate_t){0});
+            char *cursor = result->str + result->len;
+            g_string_set_size(result, result->len + size);
+            wcsrtombs(cursor, &wdir_skipped_root, size + 1, &(mbstate_t){0});
+        } else {
+            g_string_append(result, dir);
+        }
 
-        size = wcsrtombs(NULL, &wdir_skipped_root, 0, &(mbstate_t){0});
-        char *cursor = result->str + result->len;
-        g_string_set_size(result, result->len + size);
-        wcsrtombs(cursor, &wdir_skipped_root, size + 1, &(mbstate_t){0});
         g_free(wdir);
 #else
         g_string_append(result, dir);
-- 
2.41.0

On 5/10/23 08:47, Akihiko Odaki wrote:
> get_relocated_path() did not have error handling for PathCchSkipRoot()
> because a path given to get_relocated_path() was expected to be a valid
> path containing a drive letter or UNC server/share path elements on
> Windows, but sometimes it turned out otherwise.
> 
> The paths passed to get_relocated_path() are defined by macros generated
> by Meson. Meson in turn uses a prefix given by the configure script to
> generate them. For Windows, the script passes /qemu as a prefix to
> Meson by default.
> 
> As documented in docs/about/build-platforms.rst, typically MSYS2 is used
> for the build system, but it is also possible to use Linux as well. When
> MSYS2 is used, its Bash variant recognizes /qemu as a MSYS2 path, and
> converts it to a Windows path, adding the MSYS2 prefix including a drive
> letter or UNC server/share path elements. Such a conversion does not
> happen on a shell on Linux however, and /qemu will be passed as is in
> the case.
> 
> Implement a proper error handling of PathCchSkipRoot() in
> get_relocated_path() so that it can handle a path without a drive letter
> or UNC server/share path elements.
> 
> Reported-by: Stefan Weil <sw@weilnetz.de>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
> V1 -> V2: Compare against S_OK for clarity (Philippe Mathieu-Daudé)
> 
>   util/cutils.c | 18 +++++++++++-------
>   1 file changed, 11 insertions(+), 7 deletions(-)

Thanks, if Paolo doesn't take it I'll queue it in my next PR.