Re: [PATCH] middle-end/101292 - invalid memory access with warning control

[Martin Sebor <msebor@gmail.com>]

On 1/17/22 07:32, Richard Biener via Gcc-patches wrote:
> The warning control falls into the C++ trap of using a reference
> to old hashtable contents for a put operation which can end up
> re-allocating that before reading from the old freed referenced to
> source.  Fixed by introducing a temporary.

I think a better place to fix this and avoid the gotcha once and
for all is in the GCC hash_map: C++ containers are expected to
handle the insertion of own elements gracefully.

Martin

> 
> Bootstrap & regtest running on x86_64-unknown-linux-gnu.
> 
> 2022-01-17  Richard Biener  <rguenther@suse.de>
> 
> 	PR middle-end/101292
> 	* diagnostic-spec.c (copy_warning): Make sure to not
> 	reference old hashtable content on possible resize.
> 	* warning-control.cc (copy_warning): Likewise.
> ---
>   gcc/diagnostic-spec.c  | 5 ++++-
>   gcc/warning-control.cc | 3 ++-
>   2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/gcc/diagnostic-spec.c b/gcc/diagnostic-spec.c
> index a8af229d677..4341ccfaae9 100644
> --- a/gcc/diagnostic-spec.c
> +++ b/gcc/diagnostic-spec.c
> @@ -195,7 +195,10 @@ copy_warning (location_t to, location_t from)
>     else
>       {
>         if (from_spec)
> -	nowarn_map->put (to, *from_spec);
> +	{
> +	  nowarn_spec_t tem = *from_spec;
> +	  nowarn_map->put (to, tem);
> +	}
>         else
>   	nowarn_map->remove (to);
>       }
> diff --git a/gcc/warning-control.cc b/gcc/warning-control.cc
> index f9808bf4392..fa39ecab421 100644
> --- a/gcc/warning-control.cc
> +++ b/gcc/warning-control.cc
> @@ -206,7 +206,8 @@ void copy_warning (ToType to, FromType from)
>   	  gcc_assert (supp);
>   
>   	  gcc_checking_assert (nowarn_map);
> -	  nowarn_map->put (to_loc, *from_spec);
> +	  nowarn_spec_t tem = *from_spec;
> +	  nowarn_map->put (to_loc, tem);
>   	}
>         else
>   	{