Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:59108 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750857Ab2GRRjU (ORCPT ); Wed, 18 Jul 2012 13:39:20 -0400 Date: Wed, 18 Jul 2012 13:39:13 -0400 From: "J. Bruce Fields" To: Sasha Levin Cc: Trond.Myklebust@netapp.com, davem@davemloft.net, davej@redhat.com, linux-nfs@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] SUNRPC: Prevent kernel stack corruption on long values of flush Message-ID: <20120718173913.GA1298@fieldses.org> References: <1342476086-21638-1-git-send-email-levinsasha928@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1342476086-21638-1-git-send-email-levinsasha928@gmail.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, Jul 17, 2012 at 12:01:26AM +0200, Sasha Levin wrote: > The buffer size in read_flush() is too small for the longest possible values > for it. This can lead to a kernel stack corruption: Thanks! > > diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c > index 2afd2a8..f86d95e 100644 > --- a/net/sunrpc/cache.c > +++ b/net/sunrpc/cache.c > @@ -1409,11 +1409,11 @@ static ssize_t read_flush(struct file *file, char __user *buf, > size_t count, loff_t *ppos, > struct cache_detail *cd) > { > - char tbuf[20]; > + char tbuf[22]; I wonder how common this sort of calculation is in the kernel? It might provide some peace of mind to be able to write this something like char tbuf[MAXLEN_BASE10_UL + 2] /* + 2 for final "\n\0" */ --b. > unsigned long p = *ppos; > size_t len; > > - sprintf(tbuf, "%lu\n", convert_to_wallclock(cd->flush_time)); > + snprintf(tbuf, sizeof(tbuf), "%lu\n", convert_to_wallclock(cd->flush_time)); > len = strlen(tbuf); > if (p >= len) > return 0; > -- > 1.7.8.6 >