[PATCH v1] nis: Fix leak on realloc failure in nis_getnames

[Florian Weimer]

* Robbie Harwood via Libc-alpha:

> From 7aa0a9f879d5b2117beb06771bb4fdbaf25699a9 Mon Sep 17 00:00:00 2001
> From: Robbie Harwood <rharwood@redhat.com>
> Date: Wed, 28 Jul 2021 12:54:44 -0400
> Subject: [PATCH v1] nis: Fix leak on realloc failure in nis_getnames
> To: libc-alpha@sourceware.org
> Cc: kukuk@suse.de
>
> If pos >= count but realloc fails, tmp will not have been placed in
> getnames[pos] yet, and so will not be freed in free_null.  Detected
> by Coverity.
>
> Also remove misleading comment from nis_getnames(), since it actually
> did properly release getnames when out of memory.
> ---
>  nis/nis_subr.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/nis/nis_subr.c b/nis/nis_subr.c
> index dd0e30071d..6784fc353f 100644
> --- a/nis/nis_subr.c
> +++ b/nis/nis_subr.c
> @@ -103,9 +103,6 @@ count_dots (const_nis_name str)
>    return count;
>  }
>  
> -/* If we run out of memory, we don't give already allocated memory
> -   free. The overhead for bringing getnames back in a safe state to
> -   free it is to big. */
>  nis_name *
>  nis_getnames (const_nis_name name)
>  {
> @@ -271,7 +268,10 @@ nis_getnames (const_nis_name name)
>  	      nis_name *newp = realloc (getnames,
>  					(count + 1) * sizeof (char *));
>  	      if (__glibc_unlikely (newp == NULL))
> -		goto free_null;
> +		{
> +		  free (tmp);
> +		  goto free_null;
> +		}
>  	      getnames = newp;
>  	    }
>  	  getnames[pos] = tmp;

The patch looks correct to me.  (There some similar code above, but it
is already correct because the tmp ownership transfer is different.)

Would you please open a bug in Bugzilla and reference it in the commit
message.

I don't think we need to treat this as a security vulnerability (denial
of service) because since bug only happens after a memory allocation
failure, and at that point, the service is already denied, so to speak.

Thanks,
Florian