[PATCH v5 0/1] tools/hv: fcopy: Fix incorrect file path conversion

[PATCH v5 0/1] tools/hv: fcopy: Fix incorrect file path conversion

[yasuenag]

From: Yasumasa Suenaga <yasuenag@gmail.com>

Hi Naman,

Thanks a lot for your advise!
I updated commit message. This version does not have any code changes
from v4.

I hope this patch would go well.


Best regards,

Yasumasa


Yasumasa Suenaga (1):
  tools/hv: fcopy: Fix incorrect file path conversion

 tools/hv/hv_fcopy_uio_daemon.c | 37 +++++++++++++---------------------
 1 file changed, 14 insertions(+), 23 deletions(-)

-- 
2.49.0

[PATCH v5 1/1] tools/hv: fcopy: Fix incorrect file path conversion

[yasuenag]

From: Yasumasa Suenaga <yasuenag@gmail.com>

The hv_fcopy_uio_daemon fails to correctly handle file copy requests
from Windows hosts (e.g. via Copy-VMFile) due to wchar_t size
differences between Windows and Linux. On Linux, wchar_t is 32 bit,
whereas Windows uses 16 bit wide characters.

Fix this by ensuring that file transfers from host to Linux guest
succeed with correctly decoded file names and paths.

- Treats file name and path as __u16 arrays, not wchar_t*.
- Allocates fixed-size buffers (W_MAX_PATH) for converted strings
  instead of using malloc.
- Adds a check for target path length to prevent snprintf() buffer
  overflow.

Fixes: 82b0945ce2c2 ("tools: hv: Add new fcopy application based on uio driver")
Signed-off-by: Yasumasa Suenaga <yasuenag@gmail.com>
---
 tools/hv/hv_fcopy_uio_daemon.c | 37 +++++++++++++---------------------
 1 file changed, 14 insertions(+), 23 deletions(-)

diff --git a/tools/hv/hv_fcopy_uio_daemon.c b/tools/hv/hv_fcopy_uio_daemon.c
index 0198321d1..4b09ed6b6 100644
--- a/tools/hv/hv_fcopy_uio_daemon.c
+++ b/tools/hv/hv_fcopy_uio_daemon.c
@@ -62,8 +62,11 @@ static int hv_fcopy_create_file(char *file_name, char *path_name, __u32 flags)
 
 	filesize = 0;
 	p = path_name;
-	snprintf(target_fname, sizeof(target_fname), "%s/%s",
-		 path_name, file_name);
+	if (snprintf(target_fname, sizeof(target_fname), "%s/%s",
+		     path_name, file_name) >= sizeof(target_fname)) {
+		syslog(LOG_ERR, "target file name is too long: %s/%s", path_name, file_name);
+		goto done;
+	}
 
 	/*
 	 * Check to see if the path is already in place; if not,
@@ -270,7 +273,7 @@ static void wcstoutf8(char *dest, const __u16 *src, size_t dest_size)
 {
 	size_t len = 0;
 
-	while (len < dest_size) {
+	while (len < dest_size && *src) {
 		if (src[len] < 0x80)
 			dest[len++] = (char)(*src++);
 		else
@@ -282,27 +285,15 @@ static void wcstoutf8(char *dest, const __u16 *src, size_t dest_size)
 
 static int hv_fcopy_start(struct hv_start_fcopy *smsg_in)
 {
-	setlocale(LC_ALL, "en_US.utf8");
-	size_t file_size, path_size;
-	char *file_name, *path_name;
-	char *in_file_name = (char *)smsg_in->file_name;
-	char *in_path_name = (char *)smsg_in->path_name;
-
-	file_size = wcstombs(NULL, (const wchar_t *restrict)in_file_name, 0) + 1;
-	path_size = wcstombs(NULL, (const wchar_t *restrict)in_path_name, 0) + 1;
-
-	file_name = (char *)malloc(file_size * sizeof(char));
-	path_name = (char *)malloc(path_size * sizeof(char));
-
-	if (!file_name || !path_name) {
-		free(file_name);
-		free(path_name);
-		syslog(LOG_ERR, "Can't allocate memory for file name and/or path name");
-		return HV_E_FAIL;
-	}
+	/*
+	 * file_name and path_name should have same length with appropriate
+	 * member of hv_start_fcopy.
+	 */
+	char file_name[W_MAX_PATH], path_name[W_MAX_PATH];
 
-	wcstoutf8(file_name, (__u16 *)in_file_name, file_size);
-	wcstoutf8(path_name, (__u16 *)in_path_name, path_size);
+	setlocale(LC_ALL, "en_US.utf8");
+	wcstoutf8(file_name, smsg_in->file_name, W_MAX_PATH - 1);
+	wcstoutf8(path_name, smsg_in->path_name, W_MAX_PATH - 1);
 
 	return hv_fcopy_create_file(file_name, path_name, smsg_in->copy_flags);
 }
-- 
2.49.0

Re: [PATCH v5 1/1] tools/hv: fcopy: Fix incorrect file path conversion

[Naman Jain]

On 6/28/2025 7:52 AM, yasuenag@gmail.com wrote:
> From: Yasumasa Suenaga <yasuenag@gmail.com>
> 
> The hv_fcopy_uio_daemon fails to correctly handle file copy requests
> from Windows hosts (e.g. via Copy-VMFile) due to wchar_t size
> differences between Windows and Linux. On Linux, wchar_t is 32 bit,
> whereas Windows uses 16 bit wide characters.
> 
> Fix this by ensuring that file transfers from host to Linux guest
> succeed with correctly decoded file names and paths.
> 
> - Treats file name and path as __u16 arrays, not wchar_t*.
> - Allocates fixed-size buffers (W_MAX_PATH) for converted strings
>    instead of using malloc.
> - Adds a check for target path length to prevent snprintf() buffer
>    overflow.
> 
> Fixes: 82b0945ce2c2 ("tools: hv: Add new fcopy application based on uio driver")
> Signed-off-by: Yasumasa Suenaga <yasuenag@gmail.com>
> ---
>   tools/hv/hv_fcopy_uio_daemon.c | 37 +++++++++++++---------------------
>   1 file changed, 14 insertions(+), 23 deletions(-)
> 
> diff --git a/tools/hv/hv_fcopy_uio_daemon.c b/tools/hv/hv_fcopy_uio_daemon.c
> index 0198321d1..4b09ed6b6 100644
> --- a/tools/hv/hv_fcopy_uio_daemon.c
> +++ b/tools/hv/hv_fcopy_uio_daemon.c
> @@ -62,8 +62,11 @@ static int hv_fcopy_create_file(char *file_name, char *path_name, __u32 flags)
>   
>   	filesize = 0;
>   	p = path_name;
> -	snprintf(target_fname, sizeof(target_fname), "%s/%s",
> -		 path_name, file_name);
> +	if (snprintf(target_fname, sizeof(target_fname), "%s/%s",
> +		     path_name, file_name) >= sizeof(target_fname)) {
> +		syslog(LOG_ERR, "target file name is too long: %s/%s", path_name, file_name);
> +		goto done;
> +	}
>   
>   	/*
>   	 * Check to see if the path is already in place; if not,
> @@ -270,7 +273,7 @@ static void wcstoutf8(char *dest, const __u16 *src, size_t dest_size)
>   {
>   	size_t len = 0;
>   
> -	while (len < dest_size) {
> +	while (len < dest_size && *src) {
>   		if (src[len] < 0x80)
>   			dest[len++] = (char)(*src++);
>   		else
> @@ -282,27 +285,15 @@ static void wcstoutf8(char *dest, const __u16 *src, size_t dest_size)
>   
>   static int hv_fcopy_start(struct hv_start_fcopy *smsg_in)
>   {
> -	setlocale(LC_ALL, "en_US.utf8");
> -	size_t file_size, path_size;
> -	char *file_name, *path_name;
> -	char *in_file_name = (char *)smsg_in->file_name;
> -	char *in_path_name = (char *)smsg_in->path_name;
> -
> -	file_size = wcstombs(NULL, (const wchar_t *restrict)in_file_name, 0) + 1;
> -	path_size = wcstombs(NULL, (const wchar_t *restrict)in_path_name, 0) + 1;
> -
> -	file_name = (char *)malloc(file_size * sizeof(char));
> -	path_name = (char *)malloc(path_size * sizeof(char));
> -
> -	if (!file_name || !path_name) {
> -		free(file_name);
> -		free(path_name);
> -		syslog(LOG_ERR, "Can't allocate memory for file name and/or path name");
> -		return HV_E_FAIL;
> -	}
> +	/*
> +	 * file_name and path_name should have same length with appropriate
> +	 * member of hv_start_fcopy.
> +	 */
> +	char file_name[W_MAX_PATH], path_name[W_MAX_PATH];
>   
> -	wcstoutf8(file_name, (__u16 *)in_file_name, file_size);
> -	wcstoutf8(path_name, (__u16 *)in_path_name, path_size);
> +	setlocale(LC_ALL, "en_US.utf8");
> +	wcstoutf8(file_name, smsg_in->file_name, W_MAX_PATH - 1);
> +	wcstoutf8(path_name, smsg_in->path_name, W_MAX_PATH - 1);
>   
>   	return hv_fcopy_create_file(file_name, path_name, smsg_in->copy_flags);
>   }

LGTM. FYI, Fcopy daemon is broken on some systems currently. Below
change should fix it:

https://lore.kernel.org/all/20250620070618.3097-1-namjain@linux.microsoft.com/


Reviewed-by: Naman Jain <namjain@linux.microsoft.com>

Re: [PATCH v5 1/1] tools/hv: fcopy: Fix incorrect file path conversion

[Wei Liu]

On Tue, Jul 01, 2025 at 03:06:08PM +0530, Naman Jain wrote:
> 
> 
> On 6/28/2025 7:52 AM, yasuenag@gmail.com wrote:
> > From: Yasumasa Suenaga <yasuenag@gmail.com>
> > 
> > The hv_fcopy_uio_daemon fails to correctly handle file copy requests
> > from Windows hosts (e.g. via Copy-VMFile) due to wchar_t size
> > differences between Windows and Linux. On Linux, wchar_t is 32 bit,
> > whereas Windows uses 16 bit wide characters.
> > 
> > Fix this by ensuring that file transfers from host to Linux guest
> > succeed with correctly decoded file names and paths.
> > 
> > - Treats file name and path as __u16 arrays, not wchar_t*.
> > - Allocates fixed-size buffers (W_MAX_PATH) for converted strings
> >    instead of using malloc.
> > - Adds a check for target path length to prevent snprintf() buffer
> >    overflow.
> > 
> > Fixes: 82b0945ce2c2 ("tools: hv: Add new fcopy application based on uio driver")
> > Signed-off-by: Yasumasa Suenaga <yasuenag@gmail.com>
[...]
> Reviewed-by: Naman Jain <namjain@linux.microsoft.com>

Applied to hyperv-fixes. Thank you both for the patch and the review!