Re: [PATCH v2] SUNRPC: Fix READ_PLUS crasher

["J. Bruce Fields" <bfields@fieldses.org>]

This also gets through my tests without a crash.--b.

On Thu, Jun 30, 2022 at 04:48:18PM -0400, Chuck Lever wrote:
> Looks like there are still cases when "space_left - frag1bytes" can
> legitimately exceed PAGE_SIZE. Ensure that xdr->end always remains
> within the current encode buffer.
> 
> Reported-by: Bruce Fields <bfields@fieldses.org>
> Reported-by: Zorro Lang <zlang@redhat.com>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=216151
> Fixes: 6c254bf3b637 ("SUNRPC: Fix the calculation of xdr->end in xdr_get_next_encode_buffer()")
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  net/sunrpc/xdr.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
> index f87a2d8f23a7..5d2b3e6979fb 100644
> --- a/net/sunrpc/xdr.c
> +++ b/net/sunrpc/xdr.c
> @@ -984,7 +984,7 @@ static noinline __be32 *xdr_get_next_encode_buffer(struct xdr_stream *xdr,
>  	p = page_address(*xdr->page_ptr);
>  	xdr->p = p + frag2bytes;
>  	space_left = xdr->buf->buflen - xdr->buf->len;
> -	if (space_left - nbytes >= PAGE_SIZE)
> +	if (space_left - frag1bytes >= PAGE_SIZE)
>  		xdr->end = p + PAGE_SIZE;
>  	else
>  		xdr->end = p + space_left - frag1bytes;
>