From: Lorenzo Bianconi <lorenzo@kernel•org>
To: Jacob Keller <jacob.e.keller@intel•com>
Cc: Andrew Lunn <andrew+netdev@lunn•ch>,
"David S. Miller" <davem@davemloft•net>,
Eric Dumazet <edumazet@google•com>,
Jakub Kicinski <kuba@kernel•org>, Paolo Abeni <pabeni@redhat•com>,
Felix Fietkau <nbd@nbd•name>,
Matthias Brugger <matthias.bgg@gmail•com>,
AngeloGioacchino Del Regno
<angelogioacchino.delregno@collabora•com>,
Florian Westphal <fw@strlen•de>,
linux-arm-kernel@lists•infradead.org,
linux-mediatek@lists•infradead.org, netdev@vger•kernel.org
Subject: Re: [PATCH net 1/2] net: airoha: Fix use-after-free in metadata dst teardown
Date: Thu, 4 Jun 2026 23:23:16 +0200 [thread overview]
Message-ID: <aiHsxFrleJfpLeuA@lore-rh-laptop> (raw)
In-Reply-To: <21810a20-abe6-4490-969c-cfd62c4c082a@intel.com>
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> On 6/2/2026 2:21 AM, Lorenzo Bianconi wrote:
> > airoha_metadata_dst_free() runs metadata_dst_free() which frees the
> > metadata_dst with kfree() immediately, bypassing the RCU grace period.
> > In the RX path, skb_dst_set_noref() sets a non-refcounted pointer from
> > the skb to the metadata_dst. This function requires RCU read-side
> > protection and the dst must remain valid until all RCU readers complete.
> > Since metadata_dst_free() calls kfree() directly, an use-after-free can
> > occur if any skb still holds a noref pointer to the dst when the driver
> > tears it down.
> > Replace metadata_dst_free() with dst_release() which properly goes
> > through the refcount path: when the refcount drops to zero, it schedules
> > the actual free via call_rcu_hurry(), ensuring all RCU readers have
> > completed before the memory is freed.
> >
> > Fixes: af3cf757d5c9 ("net: airoha: Move DSA tag in DMA descriptor")
> > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel•org>
> > ---
> > drivers/net/ethernet/airoha/airoha_eth.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c
> > index cecd66251dba..eab6a98d62b9 100644
> > --- a/drivers/net/ethernet/airoha/airoha_eth.c
> > +++ b/drivers/net/ethernet/airoha/airoha_eth.c
> > @@ -2936,7 +2936,7 @@ static void airoha_metadata_dst_free(struct airoha_gdm_port *port)
> > if (!port->dsa_meta[i])
> > continue;
> >
> > - metadata_dst_free(port->dsa_meta[i]);
> > + dst_release(&port->dsa_meta[i]->dst);
> > }
> > }
> >
> >
>
> the port->dsa_meta is allocated using metadata_dst_alloc().. how is it
> safe to use dst_release here? Seems like we should be calling dst_alloc
> instead of metadata_dst_alloc in order to use dst_release??
We need to allocate the metadata_dst using metadata_dst_alloc() since
md_dst->u.port_info.port_id is consumed in dsa_switch_rcv() to get the
switch conduit port.
I guess it is fine to free metadata_dst running dst_release() since dst_init()
sets DST_METADATA flag and so dst_destroy() runs metadata_dst_free() after the
RCU grace period.
>
> metadata_dst_alloc does call __metadata_dst_init which calls dst_init..
>
> I guess the start of the metadata_dst structure is also the same address
> as the internal dst_entry struct...
>
> But dst_destroy does a whole lot more than metadata_dst_release so I
> don't feel confident in this actually being a drop-in replacement... It
> calls netdev_put, it calls the dst->ops->destroy, it releases child
> refs.. Or for metadata dst entries is that all basically a no-op??
__metadata_dst_init() calls dst_init() with dev = NULL so netdev_put() is a
no-op. Same for dst->ops is dst_blackhole_ops and and dst_blackhole_ops has no
destroy callback.
>
> I feel like I'm missing something here.. The driver also calls
> metadata_dst_free in the remove path and that wasn't changed by this
> patch either.
can you please explain what you mean here? we do not run metadata_dst_free()
anymore.
Regards,
Lorenzo
>
> Generally it seems like we should be using the same API to allocate as
> to release the object... This is confusing. What am I missing?
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next prev parent reply other threads:[~2026-06-04 21:23 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-02 9:21 [PATCH net 0/2] Fix use-after-free in metadata dst teardown in airoha_eth and mtk_eth_soc drivers Lorenzo Bianconi
2026-06-02 9:21 ` [PATCH net 1/2] net: airoha: Fix use-after-free in metadata dst teardown Lorenzo Bianconi
2026-06-04 17:38 ` Jacob Keller
2026-06-04 21:23 ` Lorenzo Bianconi [this message]
2026-06-04 21:53 ` Jacob Keller
2026-06-02 9:21 ` [PATCH net 2/2] net: ethernet: mtk_eth_soc: " Lorenzo Bianconi
2026-06-04 2:30 ` [PATCH net 0/2] Fix use-after-free in metadata dst teardown in airoha_eth and mtk_eth_soc drivers patchwork-bot+netdevbpf
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