[PATCH] nano-mallocr: Prevent NULL pointer de-reference in free_list

[Corinna Vinschen]

On Feb 23 07:59, Henrik Nilsson via Newlib wrote:
> On Fri, Feb 17, 2023 at 06:56:49AM +0100, Henrik Nilsson wrote:
> > The existing code checked if there was a chunk in free_list and
> > that the tail was not the next chunk.
> > 
> > The check if there is a chunk is not needed since it's already
> > known but the case of a single chunk in free_list needs to be
> > handled differently.
> > ---
> >  newlib/libc/stdlib/nano-mallocr.c | 19 ++++++++++++++-----
> >  1 file changed, 14 insertions(+), 5 deletions(-)
> > 
> > diff --git a/newlib/libc/stdlib/nano-mallocr.c b/newlib/libc/stdlib/nano-mallocr.c
> > index b2273ba60..a2b50facc 100644
> > --- a/newlib/libc/stdlib/nano-mallocr.c
> > +++ b/newlib/libc/stdlib/nano-mallocr.c
> > @@ -333,14 +333,23 @@ void * nano_malloc(RARG malloc_size_t s)
> >                 {
> >                     p->size += alloc_size;
> >  
> > -                   /* Remove chunk from free_list */
> > +                   /* Remove chunk from free_list. Since p != NULL there is
> > +                      at least one chunk */
> >                     r = free_list;
> > -                   while (r && p != r->next)
> > +                   if (r->next == NULL)
> >                     {
> > -                     r = r->next;
> > +                       /* There is only a single chunk, remove it */
> > +                       free_list = NULL;
> > +                   }
> > +                   else
> > +                   {
> > +                       /* Search for the chunk before the one to be removed */
> > +                       while (p != r->next)
> > +                       {
> > +                           r = r->next;
> > +                       }
> > +                       r->next = NULL;
> >                     }
> > -                   r->next = NULL;
> > -
> >                     r = p;
> >                 }
> >                 else
> > -- 
> > 2.34.1
> >
> Any comment on this patch?

Pushed.

Thanks,
Corinna