[PATCH] knfsd: Fix some minor sign problems in nfsd/xdr

There are a couple of tests which could possibly be confused by extremely
large numbers appearing in 'xdr' packets.  I think the closest to an exploit
you could get would be writing random data from a free page into a file - i.e.
 leak data out of kernel space.

I'm fairly sure they cannot be used for remote compromise.
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/nfsd/nfs3xdr.c

@@ -366,7 +366,8 @@ nfs3svc_decode_writeargs(struct svc_rqst *rqstp, u32 *p,
 	len = args->len = ntohl(*p++);
 
 	hdr = (void*)p - rqstp->rq_arg.head[0].iov_base;
-	if (rqstp->rq_arg.len < len + hdr)
+	if (rqstp->rq_arg.len < hdr ||
+	    rqstp->rq_arg.len - hdr < len)
 		return 0;
 
 	args->vec[0].iov_base = (void*)p;

include/linux/nfsd/xdr3.h

@@ -42,7 +42,7 @@ struct nfsd3_writeargs {
 	__u64			offset;
 	__u32			count;
 	int			stable;
-	int			len;
+	__u32			len;
 	struct kvec		vec[RPCSVC_MAXPAGES];
 	int			vlen;
 };

include/linux/sunrpc/svc.h

@@ -171,7 +171,8 @@ xdr_argsize_check(struct svc_rqst *rqstp, u32 *p)
 {
 	char *cp = (char *)p;
 	struct kvec *vec = &rqstp->rq_arg.head[0];
-	return cp - (char*)vec->iov_base <= vec->iov_len;
+	return cp >= (char*)vec->iov_base
+		&& cp <= (char*)vec->iov_base + vec->iov_len;
 }
 
 static inline int