[PATCH] setenv.c: Get rid of alloca.

[Joe Simmons-Talbott]

On Thu, Jun 29, 2023 at 11:39:08AM -0300, Adhemerval Zanella Netto wrote:
> 
> 
> On 23/06/23 12:25, Joe Simmons-Talbott via Libc-alpha wrote:
> > Use a scratch_buffer rather than alloca to avoid potential stack
> > overflow.
> > ---
> >  stdlib/setenv.c | 35 ++++++++++-------------------------
> >  1 file changed, 10 insertions(+), 25 deletions(-)
> > 
> > diff --git a/stdlib/setenv.c b/stdlib/setenv.c
> > index ba5257d3bf..90bc30b219 100644
> > --- a/stdlib/setenv.c
> > +++ b/stdlib/setenv.c
> > @@ -44,6 +44,8 @@ extern int errno;
> >  # include <unistd.h>
> >  #endif
> >  
> > +#include <scratch_buffer.h>
> > +
> 
> There is no use of scratch_buffer, the rest looks ok.

Thanks for catching that and for the review.  Fix pushed in v3.

Thanks,
Joe
> 
> >  #if !_LIBC
> >  # define __environ	environ
> >  # ifndef HAVE_ENVIRON_DECL
> > @@ -182,19 +184,14 @@ __add_to_environ (const char *name, const char *value, const char *combined,
> >  	{
> >  	  const size_t varlen = namelen + 1 + vallen;
> >  #ifdef USE_TSEARCH
> > -	  char *new_value;
> > -	  int use_alloca = __libc_use_alloca (varlen);
> > -	  if (__builtin_expect (use_alloca, 1))
> > -	    new_value = (char *) alloca (varlen);
> > -	  else
> > +	  struct scratch_buffer buf;
> > +	  scratch_buffer_init (&buf);
> > +	  if (!scratch_buffer_set_array_size (&buf, 1, varlen))
> >  	    {
> > -	      new_value = malloc (varlen);
> > -	      if (new_value == NULL)
> > -		{
> > -		  UNLOCK;
> > -		  return -1;
> > -		}
> > +	      UNLOCK;
> > +	      return -1;
> >  	    }
> > +	  char *new_value = buf.data;
> >  # ifdef _LIBC
> >  	  __mempcpy (__mempcpy (__mempcpy (new_value, name, namelen), "=", 1),
> >  		     value, vallen);
> > @@ -209,18 +206,9 @@ __add_to_environ (const char *name, const char *value, const char *combined,
> >  #endif
> >  	    {
> >  #ifdef USE_TSEARCH
> > -	      if (__glibc_unlikely (! use_alloca))
> > -		np = new_value;
> > -	      else
> > +	      np = new_value;
> >  #endif
> >  		{
> > -		  np = malloc (varlen);
> > -		  if (__glibc_unlikely (np == NULL))
> > -		    {
> > -		      UNLOCK;
> > -		      return -1;
> > -		    }
> > -
> >  #ifdef USE_TSEARCH
> >  		  memcpy (np, new_value, varlen);
> >  #else
> > @@ -234,10 +222,7 @@ __add_to_environ (const char *name, const char *value, const char *combined,
> >  	    }
> >  #ifdef USE_TSEARCH
> >  	  else
> > -	    {
> > -	      if (__glibc_unlikely (! use_alloca))
> > -		free (new_value);
> > -	    }
> > +	    scratch_buffer_free (&buf);
> >  #endif
> >  	}
> >  
>