[PATCH 3.2 074/185] nfsd4: fix xdr decoding of large non-writecompounds

[Ben Hutchings]

3.2.54-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "J. Bruce Fields" <bfields@xxxxxxxxxx>

commit 365da4adebb1c012febf81019ad3dc5bb52e2a13 upstream.

This fixes a regression from 247500820ebd02ad87525db5d9b199e5b66f6636
"nfsd4: fix decoding of compounds across page boundaries".  The previous
code was correct: argp->pagelist is initialized in
nfs4svc_deocde_compoundargs to rqstp->rq_arg.pages, and is therefore a
pointer to the page *after* the page we are currently decoding.

The reason that patch nevertheless fixed a problem with decoding
compounds containing write was a bug in the write decoding introduced by
5a80a54d21c96590d013378d8c5f65f879451ab4 "nfsd4: reorganize write
decoding", after which write decoding no longer adhered to the rule that
argp->pagelist point to the next page.

Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
[bwh: Backported to 3.2: adjust context; there is only one instance to fix]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/nfsd/nfs4xdr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -177,8 +177,8 @@ static __be32 *read_buf(struct nfsd4_com
 	 */
 	memcpy(p, argp->p, avail);
 	/* step to next page */
-	argp->pagelist++;
 	argp->p = page_address(argp->pagelist[0]);
+	argp->pagelist++;
 	if (argp->pagelen < PAGE_SIZE) {
 		argp->end = argp->p + (argp->pagelen>>2);
 		argp->pagelen = 0;

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