[v2] Check for __mprotect failure in _dl_map_segments [BZ #20831]

  * elf/dl-map-segments.h (_dl_map_segments): Check for failure
of __mprotect to change protection on the excess portion
to disallow all access.
---
v2: change formatting of __glibc_unlikely as suggested by Zack Weinberg
---
 ChangeLog             |  7 +++++++
 elf/dl-map-segments.h | 20 ++++++++++++--------
 2 files changed, 19 insertions(+), 8 deletions(-)
  

On Tue, Mar 21, 2017 at 05:20:28PM +0300, Dmitry V. Levin wrote:
> * elf/dl-map-segments.h (_dl_map_segments): Check for failure
> of __mprotect to change protection on the excess portion
> to disallow all access.
> ---
> v2: change formatting of __glibc_unlikely as suggested by Zack Weinberg
> ---
>  ChangeLog             |  7 +++++++
>  elf/dl-map-segments.h | 20 ++++++++++++--------
>  2 files changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
> index 31d6861..d36f9bd 100644
> --- a/elf/dl-map-segments.h
> +++ b/elf/dl-map-segments.h
> @@ -64,14 +64,18 @@ _dl_map_segments (struct link_map *l, int fd,
>        l->l_addr = l->l_map_start - c->mapstart;
>  
>        if (has_holes)
> -        /* Change protection on the excess portion to disallow all access;
> -           the portions we do not remap later will be inaccessible as if
> -           unallocated.  Then jump into the normal segment-mapping loop to
> -           handle the portion of the segment past the end of the file
> -           mapping.  */
> -        __mprotect ((caddr_t) (l->l_addr + c->mapend),
> -                    loadcmds[nloadcmds - 1].mapstart - c->mapend,
> -                    PROT_NONE);
> +        {
> +          /* Change protection on the excess portion to disallow all access;
> +             the portions we do not remap later will be inaccessible as if
> +             unallocated.  Then jump into the normal segment-mapping loop to
> +             handle the portion of the segment past the end of the file
> +             mapping.  */
> +          if (__glibc_unlikely
> +              (__mprotect ((caddr_t) (l->l_addr + c->mapend),
> +                           loadcmds[nloadcmds - 1].mapstart - c->mapend,
> +                           PROT_NONE) < 0))
> +            return DL_MAP_SEGMENTS_ERROR_MPROTECT;
> +        }
>  
>        l->l_contiguous = 1;
>  

There have been no more comments so I've pushed this fix.