netdev - Re: [PATCH net] net: dsa: don't leak tagger-owned storage on switch driver unbind

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Date:   Tue, 15 Nov 2022 13:57:33 -0800
From:   Saeed Mahameed <saeed@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net] net: dsa: don't leak tagger-owned storage on switch
 driver unbind

On 14 Nov 16:35, Vladimir Oltean wrote:
>In the initial commit dc452a471dba ("net: dsa: introduce tagger-owned
>storage for private and shared data"), we had a call to
>tag_ops->disconnect(dst) issued from dsa_tree_free(), which is called at
>tree teardown time.
>
>There were problems with connecting to a switch tree as a whole, so this
>got reworked to connecting to individual switches within the tree. In
>this process, tag_ops->disconnect(ds) was made to be called only from
>switch.c (cross-chip notifiers emitted as a result of dynamic tag proto
>changes), but the normal driver teardown code path wasn't replaced with
>anything.
>
>Solve this problem by adding a function that does the opposite of
>dsa_switch_setup_tag_protocol(), which is called from the equivalent
>spot in dsa_switch_teardown(). The positioning here also ensures that we
>won't have any use-after-free in tagging protocol (*rcv) ops, since the
>teardown sequence is as follows:
>
>dsa_tree_teardown
>-> dsa_tree_teardown_master
>   -> dsa_master_teardown
>      -> unsets master->dsa_ptr, making no further packets match the
>         ETH_P_XDSA packet type handler
>-> dsa_tree_teardown_ports
>   -> dsa_port_teardown
>      -> dsa_slave_destroy
>         -> unregisters DSA net devices, there is even a synchronize_net()
>            in unregister_netdevice_many()
>-> dsa_tree_teardown_switches
>   -> dsa_switch_teardown
>      -> dsa_switch_teardown_tag_protocol
>         -> finally frees the tagger-owned storage
>
>Fixes: 7f2973149c22 ("net: dsa: make tagging protocols connect to individual switches from a tree")
>Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Saeed Mahameed <saeed@...nel.org>