netdev - Re: [RFC PATCH] net/tls: Fix skb memory leak when running kTLS traffic

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Date:   Fri, 7 Jan 2022 11:12:28 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Gal Pressman <gal@...dia.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Tariq Toukan <tariqt@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [RFC PATCH] net/tls: Fix skb memory leak when running kTLS traffic

On Fri, Jan 7, 2022 at 10:51 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Sun, 2 Jan 2022 10:12:53 +0200 Gal Pressman wrote:
> > The cited Fixes commit introduced a memory leak when running kTLS
> > traffic (with/without hardware offloads).
> > I'm running nginx on the server side and wrk on the client side and get
> > the following:
> >
> >   unreferenced object 0xffff8881935e9b80 (size 224):
> >   comm "softirq", pid 0, jiffies 4294903611 (age 43.204s)
> >   hex dump (first 32 bytes):
> >     80 9b d0 36 81 88 ff ff 00 00 00 00 00 00 00 00  ...6............
> >     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >   backtrace:
> >     [<00000000efe2a999>] build_skb+0x1f/0x170
> >     [<00000000ef521785>] mlx5e_skb_from_cqe_mpwrq_linear+0x2bc/0x610 [mlx5_core]
> >     [<00000000945d0ffe>] mlx5e_handle_rx_cqe_mpwrq+0x264/0x9e0 [mlx5_core]
> >     [<00000000cb675b06>] mlx5e_poll_rx_cq+0x3ad/0x17a0 [mlx5_core]
> >     [<0000000018aac6a9>] mlx5e_napi_poll+0x28c/0x1b60 [mlx5_core]
> >     [<000000001f3369d1>] __napi_poll+0x9f/0x560
> >     [<00000000cfa11f72>] net_rx_action+0x357/0xa60
> >     [<000000008653b8d7>] __do_softirq+0x282/0x94e
> >     [<00000000644923c6>] __irq_exit_rcu+0x11f/0x170
> >     [<00000000d4085f8f>] irq_exit_rcu+0xa/0x20
> >     [<00000000d412fef4>] common_interrupt+0x7d/0xa0
> >     [<00000000bfb0cebc>] asm_common_interrupt+0x1e/0x40
> >     [<00000000d80d0890>] default_idle+0x53/0x70
> >     [<00000000f2b9780e>] default_idle_call+0x8c/0xd0
> >     [<00000000c7659e15>] do_idle+0x394/0x450
> >
> > I'm not familiar with these areas of the code, but I've added this
> > sk_defer_free_flush() to tls_sw_recvmsg() based on a hunch and it
> > resolved the issue.
> >
> > Eric, do you think this is the correct fix? Maybe we're missing a call
> > to sk_defer_free_flush() in other places as well?
>
> Any thoughts, Eric? Since the merge window is coming soon should
> we purge the defer free queue when socket is destroyed at least?
> All the .read_sock callers will otherwise risk the leaks, it seems.

It seems I missed this patch.

We might merge it, and eventually add another

WARN_ON_ONCE(!llist_empty(sk->defer_list))
sk_defer_free_flush(sk);

at socket destroy as you suggested ?

Reviewed-by: Eric Dumazet <edumazet@...gle.com>

>
> > Fixes: f35f821935d8 ("tcp: defer skb freeing after socket lock is released")
> > Signed-off-by: Gal Pressman <gal@...dia.com>
> > ---
> >  net/tls/tls_sw.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
> > index 3f271e29812f..95e774f1b91f 100644
> > --- a/net/tls/tls_sw.c
> > +++ b/net/tls/tls_sw.c
> > @@ -1990,6 +1990,7 @@ int tls_sw_recvmsg(struct sock *sk,
> >
> >  end:
> >       release_sock(sk);
> > +     sk_defer_free_flush(sk);
> >       if (psock)
> >               sk_psock_put(sk, psock);
> >       return copied ? : err;
>