[BZ,21357] unwind-dw2-fde: Call free() outside of unwind mutex

  From: Rabin Vincent <rabinv@axis.com>

__deregister_frame_info_bases() calls free() while holding a mutex which
is also used from _Unwind_Find_FDE().  This leads to a deadlock if
AddressSanitizer uses _Unwind_Backtrace() from its free()
implementation.

2017-04-06  Rabin Vincent  <rabinv@axis.com>

	[BZ #21357]
	* sysdeps/generic/unwind-dw2-fde.c (__deregister_frame_info_bases):
	Call free() outside of mutex.
  

On 06/04/2017 16:58, Rabin Vincent wrote:
> From: Rabin Vincent <rabinv@axis.com>
> 
> __deregister_frame_info_bases() calls free() while holding a mutex which
> is also used from _Unwind_Find_FDE().  This leads to a deadlock if
> AddressSanitizer uses _Unwind_Backtrace() from its free()
> implementation.
> 
> 2017-04-06  Rabin Vincent  <rabinv@axis.com>
> 
> 	[BZ #21357]
> 	* sysdeps/generic/unwind-dw2-fde.c (__deregister_frame_info_bases):
> 	Call free() outside of mutex.
> 
> diff --git a/sysdeps/generic/unwind-dw2-fde.c b/sysdeps/generic/unwind-dw2-fde.c
> index 2f0bcd2..104a255 100644
> --- a/sysdeps/generic/unwind-dw2-fde.c
> +++ b/sysdeps/generic/unwind-dw2-fde.c
> @@ -202,6 +202,7 @@ __deregister_frame_info_bases (void *begin)
>  {
>    struct object **p;
>    struct object *ob = 0;
> +  struct fde_vector *tofree = NULL;
>  
>    /* If .eh_frame is empty, we haven't registered.  */
>    if (*(uword *) begin == 0)
> @@ -225,7 +226,7 @@ __deregister_frame_info_bases (void *begin)
>  	  {
>  	    ob = *p;
>  	    *p = ob->next;
> -	    free (ob->u.sort);
> +	    tofree = ob->u.sort;
>  	    goto out;
>  	  }
>        }
> @@ -244,6 +245,7 @@ __deregister_frame_info_bases (void *begin)
>  
>   out:
>    __gthread_mutex_unlock (&object_mutex);
> +  free (tofree);
>    return (void *) ob;
>  }
>  hidden_def (__deregister_frame_info_bases)

LGTM, I assume you actually tested on some platform, right? Do you have write access?
  

On Mon, Apr 10, 2017 at 11:40:07AM -0300, Adhemerval Zanella wrote:
> On 06/04/2017 16:58, Rabin Vincent wrote:
> > 	[BZ #21357]
> > 	* sysdeps/generic/unwind-dw2-fde.c (__deregister_frame_info_bases):
> > 	Call free() outside of mutex.
> 
> LGTM, I assume you actually tested on some platform, right? Do you have write access?

Yes, I tested it on a 32-bit MIPS platform.  No, I don't have write
access.

Thanks.
  

On 13/04/2017 06:55, Rabin Vincent wrote:
> On Mon, Apr 10, 2017 at 11:40:07AM -0300, Adhemerval Zanella wrote:
>> On 06/04/2017 16:58, Rabin Vincent wrote:
>>> 	[BZ #21357]
>>> 	* sysdeps/generic/unwind-dw2-fde.c (__deregister_frame_info_bases):
>>> 	Call free() outside of mutex.
>>
>> LGTM, I assume you actually tested on some platform, right? Do you have write access?
> 
> Yes, I tested it on a 32-bit MIPS platform.  No, I don't have write
> access.
> 
> Thanks.
> 

Alright, I will check this in.