Re: [PATCH v2 04/16] skbuff: Phase out ksize() fallback for frag_size

Paolo Abeni
2022-09-25T07:17:58Z

On Fri, 2022-09-23 at 13:28 -0700, Kees Cook wrote:
> All callers of APIs that allowed a 0-sized frag_size appear to be
> passing actual size information already

AFAICS, not yet:

drivers/net/ethernet/qlogic/qed/qed_ll2.c:
skb = build_skb(buffer->data, 0); // -> __build_skb(..., 0)
// -> __build_skb_around()

drivers/net/ethernet/broadcom/bnx2.c:
skb = build_skb(data, 0);

I guess some more drivers have calls leading to

__build_skb_around(..., 0)

there are several call path to checks...

> , so this use of ksize() can
> be removed. However, just in case there is something still depending
> on this behavior, issue a WARN and fall back to as before to ksize()
> which means we'll also potentially get KASAN warnings.
>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: netdev@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> net/core/skbuff.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 0b30fbdbd0d0..84ca89c781cd 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -195,7 +195,11 @@ static void __build_skb_around(struct sk_buff *skb, void *data,
> unsigned int frag_size)
> {
> struct skb_shared_info *shinfo;
> - unsigned int size = frag_size ? : ksize(data);
> + unsigned int size = frag_size;
> +
> + /* All callers should be setting frag size now? */
> + if (WARN_ON_ONCE(size == 0))
> + size = ksize(data);

At some point in the future, I guess we could even drop this check,
right?

Thanks!

Paolo