[PATCH] Bounds checking for NFSv3 readdirplus

From Ted Phelps <phelps@dstc.edu.au>

The NFSv3 readdirplus path doesn't check to see if maxcount is less
than the size of a page before it fills it up, possibly overwriting
random bits of memory.  At least, it makes my Solaris NFSv3 client
work.

The attached patch, against 2.5.58, adds this check in a way which is
consistent with the way readdir does under both NFSv2 andNFSv3.

fs/nfsd/nfs3xdr.c

@@ -578,6 +578,9 @@ nfs3svc_decode_readdirplusargs(struct svc_rqst *rqstp, u32 *p,
 	args->dircount = ntohl(*p++);
 	args->count    = ntohl(*p++);
 
+	if (args->count > PAGE_SIZE)
+		args->count = PAGE_SIZE;
+
 	svc_take_page(rqstp);
 	args->buffer = page_address(rqstp->rq_respages[rqstp->rq_resused-1]);