netdev - Re: [PATCH net-next] net/tls: fix race condition causing kernel panic

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Message-ID: <20200521115623.134eeb83@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 21 May 2020 11:56:23 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vinay Kumar Yadav <vinay.yadav@...lsio.com>
Cc:     David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        secdev@...lsio.com
Subject: Re: [PATCH net-next] net/tls: fix race condition causing kernel
 panic

On Thu, 21 May 2020 14:28:27 +0530 Vinay Kumar Yadav wrote:
> Considering the lock in fix ("pending" is local variable), when writer reads
> pending == 0 [pending = atomic_read(&ctx->encrypt_pending); --> from tls_sw_sendmsg()],
> that means encrypt complete() [from tls_encrypt_done()] is already called.

Please indulge me with full sentences. I can't parse this.

> and if pending == 1 [pending = atomic_read(&ctx->encrypt_pending); --> from tls_sw_sendmsg()],
> that means writer is going to wait for atomic_dec_return(&ctx->decrypt_pending) and
> complete() [from tls_encrypt_done()]  to be called atomically.
> 
> This way, writer is not going to proceed to encrypt next record on CPU0 without complete().