NFSv4: Fix an Oops in the NFSv4 getacl code

Commit bf118a34 (NFSv4: include bitmap
in nfsv4 get acl data) introduces the 'acl_scratch' page for the case
where we may need to decode multi-page data. However it fails to take
into account the fact that the variable may be NULL (for the case where
we're not doing multi-page decode), and it also attaches it to the
encoding xdr_stream rather than the decoding one.

The immediate result is an Oops in nfs4_xdr_enc_getacl due to the
call to page_address() with a NULL page pointer.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Andy Adamson <andros@netapp.com>
Cc: stable@vger.kernel.org

fs/nfs/nfs4proc.c

@@ -3575,8 +3575,8 @@ static ssize_t __nfs4_get_acl_uncached(struct inode *inode, void *buf, size_t bu
 	}
 	if (npages > 1) {
 		/* for decoding across pages */
-		args.acl_scratch = alloc_page(GFP_KERNEL);
-		if (!args.acl_scratch)
+		res.acl_scratch = alloc_page(GFP_KERNEL);
+		if (!res.acl_scratch)
 			goto out_free;
 	}
 	args.acl_len = npages * PAGE_SIZE;
@@ -3612,8 +3612,8 @@ static ssize_t __nfs4_get_acl_uncached(struct inode *inode, void *buf, size_t bu
 	for (i = 0; i < npages; i++)
 		if (pages[i])
 			__free_page(pages[i]);
-	if (args.acl_scratch)
-		__free_page(args.acl_scratch);
+	if (res.acl_scratch)
+		__free_page(res.acl_scratch);
 	return ret;
 }
 

fs/nfs/nfs4xdr.c

@@ -2522,7 +2522,6 @@ static void nfs4_xdr_enc_getacl(struct rpc_rqst *req, struct xdr_stream *xdr,
 
 	xdr_inline_pages(&req->rq_rcv_buf, replen << 2,
 		args->acl_pages, args->acl_pgbase, args->acl_len);
-	xdr_set_scratch_buffer(xdr, page_address(args->acl_scratch), PAGE_SIZE);
 
 	encode_nops(&hdr);
 }
@@ -6032,6 +6031,10 @@ nfs4_xdr_dec_getacl(struct rpc_rqst *rqstp, struct xdr_stream *xdr,
 	struct compound_hdr hdr;
 	int status;
 
+	if (res->acl_scratch != NULL) {
+		void *p = page_address(res->acl_scratch);
+		xdr_set_scratch_buffer(xdr, p, PAGE_SIZE);
+	}
 	status = decode_compound_hdr(xdr, &hdr);
 	if (status)
 		goto out;

include/linux/nfs_xdr.h

@@ -614,7 +614,6 @@ struct nfs_getaclargs {
 	size_t				acl_len;
 	unsigned int			acl_pgbase;
 	struct page **			acl_pages;
-	struct page *			acl_scratch;
 	struct nfs4_sequence_args 	seq_args;
 };
 
@@ -624,6 +623,7 @@ struct nfs_getaclres {
 	size_t				acl_len;
 	size_t				acl_data_offset;
 	int				acl_flags;
+	struct page *			acl_scratch;
 	struct nfs4_sequence_res	seq_res;
 };