[PATCH] nfsd: use xdr_encode_opaque_fixed for all GETXATTR fragments

[PATCH] nfsd: use xdr_encode_opaque_fixed for all GETXATTR fragments

[Aldo Ariel Panzardo]

nfsd4_vbuf_to_stream() already uses xdr_encode_opaque_fixed() when the
final fragment is shorter than a page, but the preceding memcpy() in the
loop body does not clear XDR padding.

When the last fragment happens to be exactly PAGE_SIZE the short-fragment
branch is never entered, and the loop exits through the normal buflen
path.  If that final page-sized reservation is not word-aligned within
the XDR stream, its padding bytes are left stale.

Convert the loop memcpy to xdr_encode_opaque_fixed() and drop the now
redundant short-fragment padding block, matching the first-fragment fix.

Suggested-by: Jeff Layton <jlayton@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
---
 fs/nfsd/nfs4xdr.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index XXXXXXX..XXXXXXX 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -5963,15 +5963,7 @@ nfsd4_vbuf_to_stream(struct xdr_stream *xdr, char *buf, u32 buflen)
 		if (!p)
 			return nfserr_resource;

-		memcpy(p, buf, cplen);
-
-		if (cplen < PAGE_SIZE) {
-			/*
-			 * We're done, with a length that wasn't page
-			 * aligned, so possibly not word aligned. Pad
-			 * any trailing bytes with 0.
-			 */
-			xdr_encode_opaque_fixed(p, NULL, cplen);
-			break;
-		}
+		xdr_encode_opaque_fixed(p, buf, cplen);
+		if (cplen < PAGE_SIZE)
+			break;

 		buflen -= PAGE_SIZE;
 		buf += PAGE_SIZE;

--
2.43.0

Re: [PATCH] nfsd: use xdr_encode_opaque_fixed for all GETXATTR fragments

[Chuck Lever]

On Tue, 15 Sep 2026 14:39:01 -0300, Aldo Ariel Panzardo wrote:
> nfsd4_vbuf_to_stream() already uses xdr_encode_opaque_fixed() when the
> final fragment is shorter than a page, but the preceding memcpy() in the
> loop body does not clear XDR padding.
> 
> When the last fragment happens to be exactly PAGE_SIZE the short-fragment
> branch is never entered, and the loop exits through the normal buflen
> path.  If that final page-sized reservation is not word-aligned within
> the XDR stream, its padding bytes are left stale.
> 
> [...]

Applied to nfsd-testing, thanks!

[1/1] nfsd: use xdr_encode_opaque_fixed for all GETXATTR fragments
      commit: 802e78a4db687ee132ae9c71992490c201fdc39e

--
Chuck Lever

Re: [PATCH] nfsd: use xdr_encode_opaque_fixed for all GETXATTR fragments

[Jeff Layton]

On Tue, 2026-09-15 at 14:39 -0300, Aldo Ariel Panzardo wrote:
> nfsd4_vbuf_to_stream() already uses xdr_encode_opaque_fixed() when the
> final fragment is shorter than a page, but the preceding memcpy() in the
> loop body does not clear XDR padding.
> 
> When the last fragment happens to be exactly PAGE_SIZE the short-fragment
> branch is never entered, and the loop exits through the normal buflen
> path.  If that final page-sized reservation is not word-aligned within
> the XDR stream, its padding bytes are left stale.
> 
> Convert the loop memcpy to xdr_encode_opaque_fixed() and drop the now
> redundant short-fragment padding block, matching the first-fragment fix.
> 
> Suggested-by: Jeff Layton <jlayton@kernel.org>
> Cc: stable@vger.kernel.org
> Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
> ---
>  fs/nfsd/nfs4xdr.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index XXXXXXX..XXXXXXX 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -5963,15 +5963,7 @@ nfsd4_vbuf_to_stream(struct xdr_stream *xdr, char *buf, u32 buflen)
>  		if (!p)
>  			return nfserr_resource;
> 
> -		memcpy(p, buf, cplen);
> -
> -		if (cplen < PAGE_SIZE) {
> -			/*
> -			 * We're done, with a length that wasn't page
> -			 * aligned, so possibly not word aligned. Pad
> -			 * any trailing bytes with 0.
> -			 */
> -			xdr_encode_opaque_fixed(p, NULL, cplen);
> -			break;
> -		}
> +		xdr_encode_opaque_fixed(p, buf, cplen);
> +		if (cplen < PAGE_SIZE)
> +			break;
> 
>  		buflen -= PAGE_SIZE;
>  		buf += PAGE_SIZE;
> 
> --
> 2.43.0

Reviewed-by: Jeff Layton <jlayton@kernel.org>