nfsd: Incoming xdr_bufs may have content in tail buffer

Since the beginning, svcsock has built a received RPC Call message
by populating the xdr_buf's head, then placing the remaining
message bytes in the xdr_buf's page list. The xdr_buf's tail is
never populated.

This means that an NFSv4 COMPOUND containing an NFS WRITE operation
plus trailing operations has a page list that contains the WRITE
data payload followed by the trailing operations. NFSv4 XDR decoders
will not look in the xdr_buf's tail, ever, because svcsock never put
anything there.

To support transports that can pass the write payload in the
xdr_buf's pagelist and trailing content in the xdr_buf's tail,
introduce logic in READ_BUF that switches to the xdr_buf's tail vec
when the decoder runs out of content in rq_arg.pages.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

2 files changed, 21 insertions, 0 deletions

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 08691fe394b2..2c61c6b8ae09 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -159,6 +159,25 @@ static __be32 *read_buf(struct nfsd4_compoundargs *argp, u32 nbytes)
          */
         unsigned int avail = (char *)argp->end - (char *)argp->p;
         __be32 *p;
+
+        if (argp->pagelen == 0) {
+                struct kvec *vec = &argp->rqstp->rq_arg.tail[0];
+
+                if (!argp->tail) {
+                        argp->tail = true;
+                        avail = vec->iov_len;
+                        argp->p = vec->iov_base;
+                        argp->end = vec->iov_base + avail;
+                }
+
+                if (avail < nbytes)
+                        return NULL;
+
+                p = argp->p;
+                argp->p += XDR_QUADLEN(nbytes);
+                return p;
+        }
+
         if (avail + argp->pagelen < nbytes)
                 return NULL;
         if (avail + PAGE_SIZE < nbytes) /* need more than a page !! */
@@ -4471,6 +4490,7 @@ nfs4svc_decode_compoundargs(struct svc_rqst *rqstp, __be32 *p)
         args->end = rqstp->rq_arg.head[0].iov_base + rqstp->rq_arg.head[0].iov_len;
         args->pagelist = rqstp->rq_arg.pages;
         args->pagelen = rqstp->rq_arg.page_len;
+        args->tail = false;
         args->tmpp = NULL;
         args->to_free = NULL;
         args->ops = args->iops;
diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
index f8a0b6549a88..1e4edbf70052 100644
--- a/fs/nfsd/xdr4.h
+++ b/fs/nfsd/xdr4.h
@@ -615,6 +615,7 @@ struct nfsd4_compoundargs {
         __be32 *                        end;
         struct page **                  pagelist;
         int                             pagelen;
+        bool                            tail;
         __be32                          tmp[8];
         __be32 *                        tmpp;
         struct svcxdr_tmpbuf            *to_free;