Re: [PATCH] fs/ntfs3: return -ERANGE for short xattr buffers

[liubaolin <liubaolin12138@163.com>]

Dear maintainer,
    I found an issue where `ntfs3` returns the wrong errno when reading 
`system.ntfs_attrib` with a buffer that is too small.
When the user buffer is too small, `ntfs3` currently returns `-ENODATA`.
However, `system.ntfs_attrib` does exist in this case, and the failure 
is only caused by the user buffer being too small.
A more appropriate return value here is `-ERANGE`, not `-ENODATA`, which 
normally indicates that the xattr does not exist.

To reproduce this issue, I wrote a simple test program, 
`ntfs3_xattr_smallbuf.c`.

First, build the test program:
         gcc -O2 -Wall -o ntfs3_xattr_smallbuf ntfs3_xattr_smallbuf.c

Then reproduce it with the following steps:
         truncate -s 128M /tmp/ntfs3.img
         mkntfs -F -q /tmp/ntfs3.img
         mkdir -p /tmp/ntfs3-mnt
         mount -o loop -t ntfs3 /tmp/ntfs3.img /tmp/ntfs3-mnt
         touch /tmp/ntfs3-mnt/testfile
         ./ntfs3_xattr_smallbuf /tmp/ntfs3-mnt/testfile

On the unpatched kernel, I see the following result:
         $ ./ntfs3_xattr_smallbuf /tmp/ntfs3-mnt/testfile
         getxattr failed: errno=61 (No data available)
         `system.ntfs_attrib` does exist, but when the buffer is too 
small it returns `ENODATA`.

With this patch applied, the same test gives:
         $ ./ntfs3_xattr_smallbuf /tmp/ntfs3-mnt/testfile
         getxattr failed: errno=34 (Numerical result out of range)
         In this case, it returns `ERANGE`.

Best regards,
Baolin

***********************************************************************************************
ntfs3_xattr_smallbuf.c:
#define _GNU_SOURCE
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <sys/xattr.h>

int main(int argc, char *argv[])
{
         const char *path = argc > 1 ? argv[1] : "/tmp/ntfs3-mnt/testfile";
         char buf[1];
         ssize_t ret;

         ret = getxattr(path, "system.ntfs_attrib", buf, sizeof(buf));
         if (ret < 0) {
                 printf("getxattr failed: errno=%d (%s)\n", errno, 
strerror(errno));
                 return 1;
         }

         printf("getxattr succeeded: ret=%zd\n", ret);
         return 0;
}
**********************************************************************************************

在 2026/7/9 15:18, Baolin Liu 写道:
> From: Baolin Liu <liubaolin@kylinos.cn>
> 
> ntfs3 currently returns -ENODATA when the xattr exists
> but the user buffer is too small.
> Return -ERANGE instead.
> 
> Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
> ---
>   fs/ntfs3/xattr.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ntfs3/xattr.c b/fs/ntfs3/xattr.c
> index 9743a63a152e..0a19668e970d 100644
> --- a/fs/ntfs3/xattr.c
> +++ b/fs/ntfs3/xattr.c
> @@ -781,7 +781,7 @@ static int ntfs_getxattr(const struct xattr_handler *handler, struct dentry *de,
>   		if (!buffer) {
>   			err = sizeof(u8);
>   		} else if (size < sizeof(u8)) {
> -			err = -ENODATA;
> +			err = -ERANGE;
>   		} else {
>   			err = sizeof(u8);
>   			*(u8 *)buffer = le32_to_cpu(ni->std_fa);
> @@ -795,7 +795,7 @@ static int ntfs_getxattr(const struct xattr_handler *handler, struct dentry *de,
>   		if (!buffer) {
>   			err = sizeof(u32);
>   		} else if (size < sizeof(u32)) {
> -			err = -ENODATA;
> +			err = -ERANGE;
>   		} else {
>   			err = sizeof(u32);
>   			*(u32 *)buffer = le32_to_cpu(ni->std_fa);
> @@ -835,7 +835,7 @@ static int ntfs_getxattr(const struct xattr_handler *handler, struct dentry *de,
>   		if (!buffer) {
>   			err = sd_size;
>   		} else if (size < sd_size) {
> -			err = -ENODATA;
> +			err = -ERANGE;
>   		} else {
>   			err = sd_size;
>   			memcpy(buffer, sd, sd_size);