Re: [PATCH v3] elf: Check for empty tokens before dynamic string token expansion [BZ #22625]

[Aurelien Jarno <aurelien at aurel32 dot net>]

On 2017-12-29 16:07, Dmitry V. Levin wrote:
> On Wed, Dec 20, 2017 at 09:23:59PM +0100, Aurelien Jarno wrote:
> > The fillin_rpath function in elf/dl-load.c loops over each RPATH or
> > RUNPATH tokens and interprets empty tokens as the current directory
> > ("./"). In practice the check for empty token is done *after* the
> > dynamic string token expansion. The expansion process can return an
> > empty string for the $ORIGIN token if __libc_enable_secure is set
> > or if the path of the binary can not be determined (/proc not mounted).
> > 
> > Fix that by moving the check for empty tokens before the dynamic string
> > token expansion. In addition, check for NULL pointer or empty strings
> > return by expand_dynamic_string_token.
> > 
> > The above changes highlighted a bug in decompose_rpath, an empty array
> > is represented by the first element being NULL at the fillin_rpath
> > level, but by using a -1 pointer in decompose_rpath and other functions.
> > 
> > Changelog:
> > 	[BZ #22625]
> > 	* elf/dl-load.c (fillin_rpath): Check for empty tokens before dynamic
> > 	string token expansion. Check for NULL pointer or empty string possibly
> > 	returned by expand_dynamic_string_token.
> > 	(decompose_rpath): Check for empty path after dynamic string
> > 	token expansion.
> > ---
> >  ChangeLog     | 10 ++++++++++
> >  NEWS          |  4 ++++
> >  elf/dl-load.c | 35 ++++++++++++++++++++++++++---------
> >  3 files changed, 40 insertions(+), 9 deletions(-)
> > 
> > diff --git a/ChangeLog b/ChangeLog
> > index 35d1d102f6..0ed4d0ab15 100644
> > --- a/ChangeLog
> > +++ b/ChangeLog
> > @@ -1,3 +1,13 @@
> > +2017-12-20  Aurelien Jarno  <aurelien@aurel32.net>
> > +	    Dmitry V. Levin  <ldv@altlinux.org>
> > +
> > +	[BZ #22625]
> > +	* elf/dl-load.c (fillin_rpath): Check for empty tokens before dynamic
> > +	string token expansion. Check for NULL pointer or empty string possibly
> > +	returned by expand_dynamic_string_token.
> > +	(decompose_rpath): Check for empty path after dynamic string
> > +	token expansion.
> > +
> >  2017-12-20  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
> >  
> >  	* nptl/Makefile (libpthread-routines): Add pthread_join_common.
> > diff --git a/NEWS b/NEWS
> > index a43ff26e83..0d43e93a17 100644
> > --- a/NEWS
> > +++ b/NEWS
> > @@ -149,6 +149,10 @@ Security related changes:
> >    CVE-2017-1000366 has been applied, but it is mentioned here only because
> >    of the CVE assignment.)  Reported by Qualys.
> >  
> > +  CVE-2017-16997: Incorrect handling of RPATH or RUNPATH containing $ORIGIN
> > +  for AT_SECURE or SUID binaries could be used to load libraries from the
> > +  current directory.
> > +
> >  The following bugs are resolved with this release:
> >  
> >    [The release manager will add the list generated by
> > diff --git a/elf/dl-load.c b/elf/dl-load.c
> > index 2964464158..955eb49ecb 100644
> > --- a/elf/dl-load.c
> > +++ b/elf/dl-load.c
> > @@ -414,22 +414,31 @@ fillin_rpath (char *rpath, struct r_search_path_elem **result, const char *sep,
> >  {
> >    char *cp;
> >    size_t nelems = 0;
> > -  char *to_free;
> >  
> >    while ((cp = __strsep (&rpath, sep)) != NULL)
> >      {
> >        struct r_search_path_elem *dirp;
> > +      char *to_free = NULL;
> > +      size_t len = 0;
> >  
> > -      to_free = cp = expand_dynamic_string_token (l, cp, 1);
> > +      /* `strsep' can pass an empty string.  */
> > +      if (*cp != '\0')
> > +	{
> > +	  to_free = cp = expand_dynamic_string_token (l, cp, 1);
> >  
> > -      size_t len = strlen (cp);
> > +	  /* expand_dynamic_string_token can return NULL in case of empty
> > +	     path or memory allocation failure.  */
> > +	  if (cp == NULL)
> > +	    continue;
> >  
> > -      /* `strsep' can pass an empty string.  This has to be
> > -	 interpreted as `use the current directory'. */
> > -      if (len == 0)
> > -	{
> > -	  static const char curwd[] = "./";
> > -	  cp = (char *) curwd;
> > +         /* Compute the length after dynamic string token expansion and
> > +            ignore empty paths.  */
> > +         len = strlen (cp);
> > +         if (len == 0)
> > +           {
> > +             free (to_free);
> > +             continue;
> > +           }
> >  	}
> >  
> >        /* Remove trailing slashes (except for "/").  */
> 
> The longer I look at this hunk of fillin_rpath, the more I think
> that moving "Remove trailing slashes" and "Now add one" code inside
> "if (*cp != '\0')" statement will make fillin_rpath a bit more readable.

I am testing this solution I'll send a new version of this patch if all
is working fine.

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net

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