Re: [dpdk-dev] [PATCH] vhost: fix insecure temporary file

["Yu, Jin" <jin.yu@intel.com>]

> -----Original Message-----
> From: Bruce Richardson <bruce.richardson@intel.com>
> Sent: Tuesday, November 26, 2019 6:00 PM
> To: Yu, Jin <jin.yu@intel.com>
> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>; Bie, Tiwei
> <tiwei.bie@intel.com>; Wang, Zhihong <zhihong.wang@intel.com>;
> dev@dpdk.org; stable@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] vhost: fix insecure temporary file
> 
> On Tue, Nov 26, 2019 at 11:19:00PM +0800, Jin Yu wrote:
> > When using mkstemp(), remember to safely set the umask before to
> > restrict the resulting temporary file permissions to only the owner.
> >
> > Coverity issue: 350367
> > Fixes: d87f1a1cb7b6 ("vhost: support inflight info sharing")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Jin Yu <jin.yu@intel.com>
> > ---
> >  lib/librte_vhost/vhost_user.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/lib/librte_vhost/vhost_user.c
> > b/lib/librte_vhost/vhost_user.c index 0cfb8b792..1a68e23e3 100644
> > --- a/lib/librte_vhost/vhost_user.c
> > +++ b/lib/librte_vhost/vhost_user.c
> > @@ -1342,6 +1342,7 @@ inflight_mem_alloc(const char *name, size_t size,
> int *fd)
> >  	RTE_SET_USED(name);
> >  #endif
> >  	if (mfd == -1) {
> > +		mode_t mask = umask(0600);
> >  		mfd = mkstemp(fname);
> 
> Setting the umask is unnecessary, as if you read the man page for mkstemp:
> 
> "The file is created with permissions 0600, that is, read plus write for owner
> only."
> 
> I am aware that coverity flags this as a potential issue, but if you follow the
> link from the coverity issue to CWE-377 on cwe.mitre.org, you can find the
> following at the end of the "Notes" section:
> 
> "Finally, mkstemp() is a reasonably safe way create temporary files. It will
> attempt to create and open a unique file based on a filename template
> provided by the user combined with a series of randomly generated
> characters. If it is unable to create such a file, it will fail and return -1. On
> modern systems the file is opened using mode 0600, which means the file
> will be secure from tampering unless the user explicitly changes its access
> permissions. However, mkstemp() still suffers from the use of predictable file
> names and can leave an application vulnerable to denial of service attacks if
> an attacker causes mkstemp() to fail by predicting and pre-creating the
> filenames to be used."
> 
> So it seems that for creating temporary files, mkstemp() is probably the best
> function we can use. Therefore, I recommend not trying to patch this issue
> and just mark the issue as "ignore" in coverity.

Yes. I agree with you. I just thought we must fix the coverity issue. So I add the umask.
I would prefer to mark this issue as "ignore" in coverity.
> 
> Regards,
> /Bruce