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Message-ID: <20231016095015.GJ1501712@kernel.org>
Date: Mon, 16 Oct 2023 11:50:15 +0200
From: Simon Horman <horms@...nel.org>
To: Juntong Deng <juntong.deng@...look.com>
Cc: borisp@...dia.com, john.fastabend@...il.com, kuba@...nel.org,
davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kernel-mentees@...ts.linuxfoundation.org,
syzbot+29c22ea2d6b2c5fd2eae@...kaller.appspotmail.com
Subject: Re: [PATCH] net/tls: Fix slab-use-after-free in tls_encrypt_done
On Thu, Oct 12, 2023 at 07:02:51PM +0800, Juntong Deng wrote:
> In the current implementation, ctx->async_wait.completion is completed
> after spin_lock_bh, which causes tls_sw_release_resources_tx to
> continue executing and return to tls_sk_proto_cleanup, then return
Hi Juntong Deng,
I'm slightly confused by "causes tls_sw_release_resources_tx to continue
executing".
What I see in tls_sw_release_resources_tx() is:
/* Wait for any pending async encryptions to complete */
spin_lock_bh(&ctx->encrypt_compl_lock);
ctx->async_notify = true;
pending = atomic_read(&ctx->encrypt_pending);
spin_unlock_bh(&ctx->encrypt_compl_lock);
Am I wrong in thinking the above will block because
(the same) ctx->encrypt_compl_lock is held in tls_encrypt_done?
> to tls_sk_proto_close, and after that enter tls_sw_free_ctx_tx to kfree
> the entire struct tls_context (including ctx->encrypt_compl_lock).
>
> Since ctx->encrypt_compl_lock has been freed, subsequent spin_unlock_bh
> will result in slab-use-after-free error. Due to SMP, even using
> spin_lock_bh does not prevent tls_sw_release_resources_tx from continuing
> on other CPUs. After tls_sw_release_resources_tx is woken up, there is no
> attempt to hold ctx->encrypt_compl_lock again, therefore everything
> described above is possible.
>
> The fix is to put complete(&ctx->async_wait.completion) after
> spin_unlock_bh, making the release after the unlock. Since complete is
> only executed if pending is 0, which means this is the last record, there
> is no need to worry about race condition causing duplicate completes.
>
> Reported-by: syzbot+29c22ea2d6b2c5fd2eae@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=29c22ea2d6b2c5fd2eae
> Signed-off-by: Juntong Deng <juntong.deng@...look.com>
> ---
> net/tls/tls_sw.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
> index 270712b8d391..7abe5a6aa989 100644
> --- a/net/tls/tls_sw.c
> +++ b/net/tls/tls_sw.c
> @@ -441,6 +441,7 @@ static void tls_encrypt_done(void *data, int err)
> struct sk_msg *msg_en;
> bool ready = false;
> struct sock *sk;
> + int async_notify;
> int pending;
>
> msg_en = &rec->msg_encrypted;
> @@ -482,10 +483,11 @@ static void tls_encrypt_done(void *data, int err)
>
> spin_lock_bh(&ctx->encrypt_compl_lock);
> pending = atomic_dec_return(&ctx->encrypt_pending);
> + async_notify = ctx->async_notify;
> + spin_unlock_bh(&ctx->encrypt_compl_lock);
>
> - if (!pending && ctx->async_notify)
> + if (!pending && async_notify)
> complete(&ctx->async_wait.completion);
> - spin_unlock_bh(&ctx->encrypt_compl_lock);
>
> if (!ready)
> return;
> --
> 2.39.2
>
>
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