netdev - [PATCH net] tls: Fix context leak on tls_device

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Message-ID: <20220512091830.678684-1-maximmi@nvidia.com>
Date:   Thu, 12 May 2022 12:18:30 +0300
From:   Maxim Mikityanskiy <maximmi@...dia.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>
CC:     Paolo Abeni <pabeni@...hat.com>,
        Boris Pismenny <borisp@...dia.com>,
        "Tariq Toukan" <tariqt@...dia.com>,
        Eric Dumazet <edumazet@...gle.com>, <netdev@...r.kernel.org>,
        Maxim Mikityanskiy <maximmi@...dia.com>
Subject: [PATCH net] tls: Fix context leak on tls_device_down

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@...dia.com>
Reviewed-by: Tariq Toukan <tariqt@...dia.com>
---
 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 af875ad4a822..3919fe2c58c5 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);
-- 
2.25.1