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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Maxim Mikityanskiy <maximmi@nvidia.com>,
        Tariq Toukan <tariqt@nvidia.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15 042/102] tls: Fix context leak on tls_device_down
Date:   Mon, 16 May 2022 21:36:16 +0200
Message-Id: <20220516193625.208088763@linuxfoundation.org>
In-Reply-To: <20220516193623.989270214@linuxfoundation.org>
References: <20220516193623.989270214@linuxfoundation.org>
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From: Maxim Mikityanskiy <maximmi@nvidia.com>

[ Upstream commit 3740651bf7e200109dd42d5b2fb22226b26f960a ]

The commit cited below claims to fix a use-after-free condition after
tls_device_down. Apparently, the description wasn't fully accurate. The
context stayed alive, but ctx->netdev became NULL, and the offload was
torn down without a proper fallback, so a bug was present, but a
different kind of bug.

Due to misunderstanding of the issue, the original patch dropped the
refcount_dec_and_test line for the context to avoid the alleged
premature deallocation. That line has to be restored, because it matches
the refcount_inc_not_zero from the same function, otherwise the contexts
that survived tls_device_down are leaked.

This patch fixes the described issue by restoring refcount_dec_and_test.
After this change, there is no leak anymore, and the fallback to
software kTLS still works.

Fixes: c55dcdd435aa ("net/tls: Fix use-after-free after the TLS device goes down and up")
Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://lore.kernel.org/r/20220512091830.678684-1-maximmi@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/tls/tls_device.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
index a40553e83f8b..f3e3d009cf1c 100644
--- a/net/tls/tls_device.c
+++ b/net/tls/tls_device.c
@@ -1347,7 +1347,10 @@ static int tls_device_down(struct net_device *netdev)
 
 		/* Device contexts for RX and TX will be freed in on sk_destruct
 		 * by tls_device_free_ctx. rx_conf and tx_conf stay in TLS_HW.
+		 * Now release the ref taken above.
 		 */
+		if (refcount_dec_and_test(&ctx->refcount))
+			tls_device_free_ctx(ctx);
 	}
 
 	up_write(&device_offload_lock);
-- 
2.35.1