svn commit: r349890 - head/contrib/telnet/telnet

[Shawn Webb]

On Wed, Jul 10, 2019 at 04:40:25PM -0600, Warner Losh wrote:
> On Wed, Jul 10, 2019 at 4:29 PM Shawn Webb <shawn.webb at hardenedbsd.org>
> wrote:
> 
> > On Wed, Jul 10, 2019 at 04:22:18PM -0400, Shawn Webb wrote:
> > > On Wed, Jul 10, 2019 at 03:19:44PM -0500, Justin Hibbits wrote:
> > > > On Wed, 10 Jul 2019 15:55:48 -0400
> > > > Shawn Webb <shawn.webb at hardenedbsd.org> wrote:
> > > >
> > > > > On Wed, Jul 10, 2019 at 05:42:04PM +0000, Philip Paeps wrote:
> > > > > > Author: philip
> > > > > > Date: Wed Jul 10 17:42:04 2019
> > > > > > New Revision: 349890
> > > > > > URL: https://svnweb.freebsd.org/changeset/base/349890
> > > > > >
> > > > > > Log:
> > > > > >   telnet: fix a couple of snprintf() buffer overflows
> > > > > >
> > > > > >   Obtained from:        Juniper Networks
> > > > > >   MFC after:    1 week
> > > > > >
> > > > > > Modified:
> > > > > >   head/contrib/telnet/telnet/commands.c
> > > > > >   head/contrib/telnet/telnet/telnet.c
> > > > > >   head/contrib/telnet/telnet/utilities.c
> > > > > >
> > > > > > Modified: head/contrib/telnet/telnet/commands.c
> > > > > >
> > ==============================================================================
> > > > > > --- head/contrib/telnet/telnet/commands.c       Wed Jul 10
> > > > > > 17:21:59 2019   (r349889) +++
> > > > > > head/contrib/telnet/telnet/commands.c   Wed Jul 10 17:42:04
> > > > > > 2019    (r349890) @@ -1655,10 +1655,11 @@ env_init(void) char
> > > > > > hbuf[256+1]; char *cp2 = strchr((char *)ep->value, ':');
> > > > > >
> > > > > > -               gethostname(hbuf, 256);
> > > > > > -               hbuf[256] = '\0';
> > > > > > -               cp = (char *)malloc(strlen(hbuf) + strlen(cp2) +
> > > > > > 1);
> > > > > > -               sprintf((char *)cp, "%s%s", hbuf, cp2);
> > > > > > +               gethostname(hbuf, sizeof(hbuf));
> > > > > > +               hbuf[sizeof(hbuf)-1] = '\0';
> > > > > > +                unsigned int buflen = strlen(hbuf) + strlen(cp2) +
> > > > > > 1;
> > > > >
> > > > > buflen should be defined with the rest of the variables in the code
> > > > > block above this one.
> > > >
> > > > Agreed.
> > > >
> > > > >
> > > > > > +               cp = (char *)malloc(sizeof(char)*buflen);
> > > > >
> > > > > Lack of NULL check here leads to
> > > > >
> > > > > > +               snprintf((char *)cp, buflen, "%s%s", hbuf, cp2);
> > > > >
> > > > > potential NULL pointer deref here.
> > > >
> > > > I'm not sure if this is actually a problem.  env_init() is called
> > > > exactly once, at the beginning of main(), and the environment size is
> > > > fully constrained by the OS.
> > > >
> > > > That said, this file it the only one in this component that does not
> > > > check the return value of malloc().  All other uses, outside of this
> > > > file, check and error.
> > >
> > > While fixing the style(9) violation above, we could still take care of
> > > the potential NULL deref at the same time. If anything, just for code
> > > correctness reasons?
> >
> > Here's a patch:
> >
> > https://gist.github.com/579685c0252673c3ad92d2536c3486c7
> 
> 
> Any reason to not use asprintf instead of malloc + snprintf?

Because the existing code already used malloc + snprintf. And this is
contrib/telnet/telnet, which arguably should be `rm -rf`ed. ;)

The bike shed is now glow-in-the-dark neon green.

Thanks,

-- 
Shawn Webb
Cofounder / Security Engineer
HardenedBSD

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