Re: [PATCH net] ppp: fix memory leak in pad_compress_skb

Eric Dumazet <[email protected]> Wed, 3 Sep 2025 04:18:38 -0700

Newsgroups	org.kernel.vger.linux-ppp,org.kernel.vger.linux-kernel,org.kernel.vger.netdev
Message-ID	<CANn89iLKpJaF0VcWxqCUuouJw8mZ4Fjk_cc89yMmuZWCLx70-w@mail.gmail.com>

On Wed, Sep 3, 2025 at 3:07 AM Qingfang Deng <[email protected]> wrote:
>
> If alloc_skb() fails in pad_compress_skb(), it returns NULL without
> releasing the old skb. The caller does:
>
>     skb = pad_compress_skb(ppp, skb);
>     if (!skb)
>         goto drop;
>
> drop:
>     kfree_skb(skb);
>
> When pad_compress_skb() returns NULL, the reference to the old skb is
> lost and kfree_skb(skb) ends up doing nothing, leading to a memory leak.
>
> Align pad_compress_skb() semantics with realloc(): only free the old
> skb if allocation and compression succeed.  At the call site, use the
> new_skb variable so the original skb is not lost when pad_compress_skb()
> fails.
>
> Fixes: b3f9b92a6ec1 ("[PPP]: add PPP MPPE encryption module")
> Signed-off-by: Qingfang Deng <[email protected]>
> ---

Reviewed-by: Eric Dumazet <[email protected]>