On Thu, 2022-09-01 at 15:10 -0400, Chuck Lever wrote:
> Since before the git era, NFSD has conserved the number of pages
> held by each nfsd thread by combining the RPC receive and send
> buffers into a single array of pages. This works because there are
> no cases where an operation needs a large RPC Call message and a
> large RPC Reply at the same time.
>
> Once an RPC Call has been received, svc_process() updates
> svc_rqst::rq_res to describe the part of rq_pages that can be
> used for constructing the Reply. This means that the send buffer
> (rq_res) shrinks when the received RPC record containing the RPC
> Call is large.
>
> A client can force this shrinkage on TCP by sending a correctly-
> formed RPC Call header contained in an RPC record that is
> excessively large. The full maximum payload size cannot be
> constructed in that case.
>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> fs/nfsd/nfs3proc.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
> index 7a159785499a..5b1e771238b3 100644
> --- a/fs/nfsd/nfs3proc.c
> +++ b/fs/nfsd/nfs3proc.c
> @@ -150,7 +150,6 @@ nfsd3_proc_read(struct svc_rqst *rqstp)
> {
> struct nfsd3_readargs *argp = rqstp->rq_argp;
> struct nfsd3_readres *resp = rqstp->rq_resp;
> - u32 max_blocksize = svc_max_payload(rqstp);
> unsigned int len;
> int v;
>
> @@ -159,7 +158,8 @@ nfsd3_proc_read(struct svc_rqst *rqstp)
> (unsigned long) argp->count,
> (unsigned long long) argp->offset);
>
> - argp->count = min_t(u32, argp->count, max_blocksize);
> + argp->count = min_t(u32, argp->count, svc_max_payload(rqstp));
> + argp->count = min_t(u32, argp->count, rqstp->rq_res.buflen);
> if (argp->offset > (u64)OFFSET_MAX)
> argp->offset = (u64)OFFSET_MAX;
> if (argp->offset + argp->count > (u64)OFFSET_MAX)
>
>
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
