On Sun, Jun 05, 2022 at 03:58:25PM -0400, Chuck Lever wrote:
> I found that NFSD's new NFSv3 READDIRPLUS XDR encoder was screwing up
> right at the end of the page array. xdr_get_next_encode_buffer() does
> not compute the value of xdr->end correctly:
>
> * The check to see if we're on the final available page in xdr->buf
> needs to account for the space consumed by @nbytes.
>
> * The new xdr->end value needs to account for the portion of @nbytes
> that is to be encoded into the previous buffer.
>
> Fixes: 2825a7f90753 ("nfsd4: allow encoding across page boundaries")
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> net/sunrpc/xdr.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
> index df194cc07035..b57cf9df4de8 100644
> --- a/net/sunrpc/xdr.c
> +++ b/net/sunrpc/xdr.c
> @@ -979,7 +979,11 @@ static __be32 *xdr_get_next_encode_buffer(struct xdr_stream *xdr,
> */
> xdr->p = (void *)p + frag2bytes;
> space_left = xdr->buf->buflen - xdr->buf->len;
> - xdr->end = (void *)p + min_t(int, space_left, PAGE_SIZE);
> + if (space_left - nbytes >= PAGE_SIZE)
> + xdr->end = (void *)p + PAGE_SIZE;
> + else
> + xdr->end = (void *)p + space_left - frag1bytes;
> +
I think that's right.
Couldn't you just make that
- xdr->end = (void *)p + min_t(int, space_left, PAGE_SIZE);
+ xdr->end = (void *)p + min_t(int, space_left - nbytes, PAGE_SIZE);
?
(Note we know space_left >= nbytes from the second "if" of this
function.)
No strong opinion either way, really, I just wonder if I'm missing
something.
--b.
> xdr->buf->page_len += frag2bytes;
> xdr->buf->len += nbytes;
> return p;
>
