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

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Message-Id: <20200519.121641.1552016505379076766.davem@davemloft.net>
Date:   Tue, 19 May 2020 12:16:41 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     vinay.yadav@...lsio.com
Cc:     netdev@...r.kernel.org, kuba@...nel.org, secdev@...lsio.com
Subject: Re: [PATCH net-next] net/tls: fix race condition causing kernel
 panic

From: Vinay Kumar Yadav <vinay.yadav@...lsio.com>
Date: Tue, 19 May 2020 13:13:27 +0530

> +		spin_lock_bh(&ctx->encrypt_compl_lock);
> +		pending = atomic_read(&ctx->encrypt_pending);
> +		spin_unlock_bh(&ctx->encrypt_compl_lock);

The sequence:

	lock();
	x = p->y;
	unlock();

Does not fix anything, and is superfluous locking.

The value of p->y can change right after the unlock() call, so you
aren't protecting the atomic'ness of the read and test sequence
because the test is outside of the lock.