Re: [PATCH 1/1] libctf: Fix double free in ctf_link_add_cu_mapping.

[Nick Alcock <nick.alcock@oracle.com>]

On 8 Dec 2022, Alan Modra via Binutils stated:

> On Wed, Dec 07, 2022 at 03:11:37PM +0100, Felix Willgerodt via Binutils wrote:
>> This fixes a potential double free which can occur if we jump to
>> oom_noerrno after the first free.
>> 
>> I am not very familiar with libctf, so any comments are welcome.
>> I am wondering if the right solution wouldn't be to free both t and f before
>> the "return 0".  But I didn't fully understand the code and saw that other
>> users of ctf_dynhash_insert() also don't free the key manually.
>
> No, they can't be freed if successfully inserted into the hash table,
> but "t" should indeed be freed if already inserted.  I'm applying the
> following fix.
>
> 	* ctf-link.c (ctf_link_add_cu_mapping): Set t NULL after free.
>
> diff --git a/libctf/ctf-link.c b/libctf/ctf-link.c
> index 702f2b4d5fe..902b4408cd6 100644
> --- a/libctf/ctf-link.c
> +++ b/libctf/ctf-link.c
> @@ -431,7 +431,10 @@ ctf_link_add_cu_mapping (ctf_dict_t *fp, const char *from, const char *to)
>  	}
>      }
>    else
> -    free (t);
> +    {
> +      free (t);
> +      t = NULL;
> +    }
>  
>    if (ctf_dynhash_insert (one_out, f, NULL) < 0)
>      {

Looks good! Sorry about that. This function has been subject to more
OOM-related memory allocation problems than everything else in libctf
combined :/

-- 
NULL && (void)