Re: [PATCH v1] nscd: Fix double free in netgroupcache [BZ #27462]

[Carlos O'Donell <carlos@redhat.com>]

On 2/25/21 4:13 PM, DJ Delorie via Libc-alpha wrote:
> 
> In commit 745664bd798ec8fd50438605948eea594179fba1 a use-after-free
> was fixed, but this led to an occasional double-free.  This patch
> tracks the "live" allocation better.
> 
> Tested manually by a third party.

This looks like it should be logically the correct fix. There are only
two xrealloc's that I see that could impact the buffer reuse here and
we need to track the update to the pointer.

LGTM.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> Related: RHBZ 1927877
> ---
>  nscd/netgroupcache.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/nscd/netgroupcache.c b/nscd/netgroupcache.c
> index dba6ceec1b..ad2daddafd 100644
> --- a/nscd/netgroupcache.c
> +++ b/nscd/netgroupcache.c
> @@ -248,7 +248,7 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
>  					     : NULL);
>  				    ndomain = (ndomain ? newbuf + ndomaindiff
>  					       : NULL);
> -				    buffer = newbuf;
> +				    *tofreep = buffer = newbuf;
>  				  }
>  
>  				nhost = memcpy (buffer + bufused,
> @@ -319,7 +319,7 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
>  		    else if (status == NSS_STATUS_TRYAGAIN && e == ERANGE)
>  		      {
>  			buflen *= 2;
> -			buffer = xrealloc (buffer, buflen);
> +			*tofreep = buffer = xrealloc (buffer, buflen);
>  		      }
>  		    else if (status == NSS_STATUS_RETURN
>  			     || status == NSS_STATUS_NOTFOUND
> 


-- 
Cheers,
Carlos.