[PATCH v1] SUNRPC: Fix NFS READs that start at non-page-aligned offsets

[PATCH v1] SUNRPC: Fix NFS READs that start at non-page-aligned offsets

[Chuck Lever]

Anj Duvnjak reports that the Kodi.tv NFS client is not able to read
video files from a v5.10.11 Linux NFS server.

The new sendpage-based TCP sendto logic was not attentive to non-
zero page_base values. nfsd_splice_read() sets that field when a
READ payload starts in the middle of a page.

The Linux NFS client rarely emits an NFS READ that is not page-
aligned. All of my testing so far has been with Linux clients, so I
missed this one.

Reported-by: A. Duvnjak <avian@extremenerds.net>
BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=211471
Fixes: 4a85a6a3320b ("SUNRPC: Handle TCP socket sends with kernel_sendpage() again")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/svcsock.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index c9766d07eb81..5a809c64dc7b 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -1113,14 +1113,15 @@ static int svc_tcp_sendmsg(struct socket *sock, struct msghdr *msg,
 		unsigned int offset, len, remaining;
 		struct bio_vec *bvec;
 
-		bvec = xdr->bvec;
-		offset = xdr->page_base;
+		bvec = xdr->bvec + (xdr->page_base >> PAGE_SHIFT);
+		offset = offset_in_page(xdr->page_base);
 		remaining = xdr->page_len;
 		flags = MSG_MORE | MSG_SENDPAGE_NOTLAST;
 		while (remaining > 0) {
 			if (remaining <= PAGE_SIZE && tail->iov_len == 0)
 				flags = 0;
-			len = min(remaining, bvec->bv_len);
+
+			len = min(remaining, bvec->bv_len - offset);
 			ret = kernel_sendpage(sock, bvec->bv_page,
 					      bvec->bv_offset + offset,
 					      len, flags);

Re: [PATCH v1] SUNRPC: Fix NFS READs that start at non-page-aligned offsets

[A. Duvnjak]

I tried this patch on 5.10.12 (which would normally produce streaming errors).  So far it works well.   Have tried it in the three situations that would previously cause issues -  Kodi on Windows,  Kodi on Mac, and the Windows 10 NFS client with VLC.  All check out fine.


> On 1 Feb 2021, at 11:53 am, Chuck Lever <chuck.lever@oracle.com> wrote:
> 
> Anj Duvnjak reports that the Kodi.tv NFS client is not able to read
> video files from a v5.10.11 Linux NFS server.
> 
> The new sendpage-based TCP sendto logic was not attentive to non-
> zero page_base values. nfsd_splice_read() sets that field when a
> READ payload starts in the middle of a page.
> 
> The Linux NFS client rarely emits an NFS READ that is not page-
> aligned. All of my testing so far has been with Linux clients, so I
> missed this one.
> 
> Reported-by: A. Duvnjak <avian@extremenerds.net>
> BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=211471
> Fixes: 4a85a6a3320b ("SUNRPC: Handle TCP socket sends with kernel_sendpage() again")
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
> net/sunrpc/svcsock.c |    7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
> index c9766d07eb81..5a809c64dc7b 100644
> --- a/net/sunrpc/svcsock.c
> +++ b/net/sunrpc/svcsock.c
> @@ -1113,14 +1113,15 @@ static int svc_tcp_sendmsg(struct socket *sock, struct msghdr *msg,
> 		unsigned int offset, len, remaining;
> 		struct bio_vec *bvec;
> 
> -		bvec = xdr->bvec;
> -		offset = xdr->page_base;
> +		bvec = xdr->bvec + (xdr->page_base >> PAGE_SHIFT);
> +		offset = offset_in_page(xdr->page_base);
> 		remaining = xdr->page_len;
> 		flags = MSG_MORE | MSG_SENDPAGE_NOTLAST;
> 		while (remaining > 0) {
> 			if (remaining <= PAGE_SIZE && tail->iov_len == 0)
> 				flags = 0;
> -			len = min(remaining, bvec->bv_len);
> +
> +			len = min(remaining, bvec->bv_len - offset);
> 			ret = kernel_sendpage(sock, bvec->bv_page,
> 					      bvec->bv_offset + offset,
> 					      len, flags);
> 
>