Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:60627 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752183Ab2GRVIb (ORCPT ); Wed, 18 Jul 2012 17:08:31 -0400 Date: Wed, 18 Jul 2012 17:08:25 -0400 From: "J. Bruce Fields" To: Jim Rees Cc: Sasha Levin , 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: <20120718210825.GA3145@fieldses.org> References: <1342476086-21638-1-git-send-email-levinsasha928@gmail.com> <20120718173913.GA1298@fieldses.org> <20120718200049.GA17964@umich.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20120718200049.GA17964@umich.edu> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, Jul 18, 2012 at 04:00:49PM -0400, Jim Rees wrote: > J. Bruce Fields wrote: > > 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" */ > > You could use something like: > > char tbuf[sizeof (unsigned long) * 24 / 10 + 1 + 2]; /* + 2 for final "\n\0" */ > > since there are roughly 10 bits for every 3 decimal digits. So we could do something like this. OK, I'm not sure I care enough. --b. diff --git a/include/linux/string.h b/include/linux/string.h index e033564..ed34180 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -126,6 +126,10 @@ extern void argv_free(char **argv); extern bool sysfs_streq(const char *s1, const char *s2); extern int strtobool(const char *s, bool *res); +/* length of the decimal representation of an unsigned integer. Just an + * approximation, but it's right for types of size 1 to 36 bytes: */ +#define base10len(i) (sizeof(i) * 24 / 10 + 1) + #ifdef CONFIG_BINARY_PRINTF int vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args); int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf); diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c index 2afd2a8..1dcd2b3 100644 --- a/net/sunrpc/cache.c +++ b/net/sunrpc/cache.c @@ -1409,7 +1409,7 @@ 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[base10len(unsigned long) + 2]; unsigned long p = *ppos; size_t len;