netdev - Re: [PATCH bpf] libbpf: always NULL out pobj in bpf_prog_load

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Date:   Thu, 2 May 2019 16:03:30 +0000
From:   Martin Lau <kafai@...com>
To:     Lorenz Bauer <lmb@...udflare.com>
CC:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>
Subject: Re: [PATCH bpf] libbpf: always NULL out pobj in bpf_prog_load_xattr

On Thu, May 02, 2019 at 11:49:32AM -0400, Lorenz Bauer wrote:
> Currently, code like the following segfaults if bpf_prog_load_xattr
> returns an error:
> 
>     struct bpf_object *obj;
> 
>     err = bpf_prog_load_xattr(&attr, &obj, &prog_fd);
>     bpf_object__close(obj);
This is a bug.  err should always be checked first before
using obj or prog_fd.  If there is err, calling bpf_object__close(NULL)
is another redundancy.

>     if (err)
>         ...
> 
> Unconditionally reset pobj to NULL at the start of the function
> to fix this.
Hence, this change is unnecessary.

> 
> Signed-off-by: Lorenz Bauer <lmb@...udflare.com>
> ---
>  tools/lib/bpf/libbpf.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 11a65db4b93f..2ddf3212b8f7 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -3363,6 +3363,8 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
>  	struct bpf_map *map;
>  	int err;
>  
> +	*pobj = NULL;
> +
>  	if (!attr)
>  		return -EINVAL;
>  	if (!attr->file)
> -- 
> 2.19.1
>