nfsd4: reserve space before inlining 0-copy pages

Once we've included page-cache pages in the encoding it's difficult to
remove them and restart encoding.  (xdr_truncate_encode doesn't handle
that case.)  So, make sure we'll have adequate space to finish the
operation first.

For now COMPOUND_SLACK_SPACE checks should prevent this case happening,
but we want to remove those checks.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 799a90479487..8728715cd6e8 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3071,6 +3071,10 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
         if (!p)
                 return nfserr_resource;
 
+        /* Make sure there will be room for padding if needed: */
+        if (xdr->end - xdr->p < 1)
+                return nfserr_resource;
+
         maxcount = svc_max_payload(resp->rqstp);
         if (maxcount > read->rd_length)
                 maxcount = read->rd_length;
@@ -3122,8 +3126,6 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
         resp->xdr.buf->tail[0].iov_len = 0;
         if (maxcount&3) {
                 p = xdr_reserve_space(xdr, 4);
-                if (!p)
-                        return nfserr_resource;
                 WRITE32(0);
                 resp->xdr.buf->tail[0].iov_base += maxcount&3;
                 resp->xdr.buf->tail[0].iov_len = 4 - (maxcount&3);
@@ -3156,6 +3158,9 @@ nfsd4_encode_readlink(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd
         if (!p)
                 return nfserr_resource;
 
+        if (xdr->end - xdr->p < 1)
+                return nfserr_resource;
+
         /*
          * XXX: By default, the ->readlink() VFS op will truncate symlinks
          * if they would overflow the buffer.  Is this kosher in NFSv4?  If
@@ -3182,8 +3187,6 @@ nfsd4_encode_readlink(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd
         resp->xdr.buf->tail[0].iov_len = 0;
         if (maxcount&3) {
                 p = xdr_reserve_space(xdr, 4);
-                if  (!p)
-                        return nfserr_resource;
                 WRITE32(0);
                 resp->xdr.buf->tail[0].iov_base += maxcount&3;
                 resp->xdr.buf->tail[0].iov_len = 4 - (maxcount&3);