netdev - RE: [PATCH] net/rds: using strlcpy instead of strncpy

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Message-ID: <1362422090.2956.18.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Mon, 4 Mar 2013 18:34:50 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	David Laight <David.Laight@...LAB.COM>
CC:	Chen Gang <gang.chen@...anux.com>,
	<venkat.x.venkatsubra@...cle.com>,
	David Miller <davem@...emloft.net>, <rds-devel@....oracle.com>,
	netdev <netdev@...r.kernel.org>
Subject: RE: [PATCH] net/rds: using strlcpy instead of strncpy

On Mon, 2013-03-04 at 18:32 +0000, Ben Hutchings wrote:
> On Thu, 2013-02-28 at 09:36 +0000, David Laight wrote:
> > >   when src strlen is sizeof(ctr.name) - 1, the dest str is not '\0' end.
> > >   better use strlcpy instead.
> > > 
> > > Signed-off-by: Chen Gang <gang.chen@...anux.com>
> > > ---
> > >  net/rds/stats.c |    2 +-
> > >  1 files changed, 1 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/net/rds/stats.c b/net/rds/stats.c
> > > index 7be790d..b9ac1df 100644
> > > --- a/net/rds/stats.c
> > > +++ b/net/rds/stats.c
> > > @@ -86,7 +86,7 @@ void rds_stats_info_copy(struct rds_info_iterator *iter,
> > > 
> > >  	for (i = 0; i < nr; i++) {
> > >  		BUG_ON(strlen(names[i]) >= sizeof(ctr.name));
> > > -		strncpy(ctr.name, names[i], sizeof(ctr.name) - 1);
> > > +		strlcpy(ctr.name, names[i], sizeof(ctr.name));
> > >  		ctr.value = values[i];
> > > 
> > 
> > If the target buffer ends up being copied to userspace that
> > might lead to random kernel memory being leaked.
> 
> Seems it is.  The last byte of 'name' is not currently initialised and
> therefore is already leaked to userland.
> 
> But it's OK because rds_info_copy() uses memcpy() not __copy_to_user(),
> so SMAP will block this leak. :-)

Or not, as kmap() presumably evades that.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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