From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tim Deegan <tim@xen.org>
Subject: Re: [PATCH 3 of 3 RESEND] libxl: Warn that
	/usr/bin/pygrub is deprecated
Date: Thu, 10 May 2012 12:44:14 +0100
Message-ID: <20120510114414.GC73773@ocelot.phlegethon.org>
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To: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: George Dunlap <george.dunlap@eu.citrix.com>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, Ian Campbell <Ian.Campbell@citrix.com>
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At 12:36 +0100 on 10 May (1336653395), Ian Jackson wrote:
> George Dunlap writes ("Re: [Xen-devel] [PATCH 3 of 3 RESEND] libxl: Warn that /usr/bin/pygrub is deprecated"):
> > On 09/05/12 14:43, Ian Campbell wrote:
> > > On Wed, 2012-05-09 at 11:51 +0100, George Dunlap wrote:
> > >> +    if ( !strncmp(info->u.pv.bootloader, "/usr/bin/pygrub", 20) )
> > > Why strncmp and not just strcmp? And why 20? AFAIK
> > > strlen("/usr/bin/pygrub") == 15 or 16 or so...
> >
> > ISTR in the past build processes throwing warnings that strcmp() is 
> > unsafe, and since warnings turn to errors, pre-emptively used the "safe" 
> > version instead.
> 
> Boggle.  Any such build processes need to be taken out and shot.
> There is nothing wrong with strcmp.  Are you sure you're not thinking
> of strcat or sprintf ?

If the user controlled both the length and contents of
info->u.pv.bootloader, it could cause this to overrun that buffer and
cause a SEGV.  So, sadly, strcmp goes on the 'just never use it' list
for many people.

Tim.