From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 82FE240D572; Sat, 20 Jun 2026 16:30:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781973035; cv=none; b=IebzE3U9iuq+xSYMcy1j/Oh/pAo3aOeCminH4VnzjXGRnoIamSsKnXB0KZBXru8U8wyO+UxI3WeEuCBj1GRVo26918ySXW9UGFx3tqADOjfJKO7qyvkh1tAu8GPuhEcPwgPxXTvJzasxCTyMnuzK/kNdIxXkjANiur5Y/VwsAcA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781973035; c=relaxed/simple; bh=3Dpmmerb0QG1G8KOpjCvUTZKf0T5mNd9JG1LlDJ0JzM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=kHmWPBXnXqlKMNKe5392TG0OnV/RVx1p8v4gSffHXDV6GR41T4S5wgcQBbLv9RIMajmZ13PnGXRaRkDhcQ+ZSTE0AeqWJvLfsWOPSfGRnknM6XJRVmQot2Ct2ssGv69i0XV8LWiLvIEK0EDE5Q+gJIy/2xoZnNPuhmDN0u3QRoE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fWXNKPZl; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="fWXNKPZl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D3C4E1F000E9; Sat, 20 Jun 2026 16:30:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781973034; bh=D6t63Jy9/sgsYx1uJL6I1MjmSXoE7TCkLo+nXd+KPuE=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=fWXNKPZlBWyTdQbXzoThXH/SeBRUhorUJKPsfN9xAPKoG18QJhs0snK4JG63X1qVz DRKCkOEr0kbqBzik+DTrrjTGwBlbqhU1Wngff+WgfdG3ti6dAc64vP3XRd+tOcJQ8X oG3Iw10H87jzBYATA1+GK/WvnySc2EQuSOdaFauRHoInJq4E+8br/cDv6xKp4++/80 VGTRtUO9n93Not0f5Q2r4VLEDSIVjA3pAle+iii3wQxHsNwBjZ3wS4zZNN+gqZad3S 5Co0ua3fxYiceYokKoHpicoxGDja/XL7V0svTXndP5nDm74+VCs3RQQsFaxet02VGD 7YSzRd+MHSHlw== Date: Sat, 20 Jun 2026 17:30:28 +0100 From: Simon Horman To: Doruk Tan Ozturk Cc: saeedm@nvidia.com, leon@kernel.org, tariqt@nvidia.com, mbloch@nvidia.com, sd@queasysnail.net, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, borisp@nvidia.com, raeds@nvidia.com, ehakim@nvidia.com, netdev@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH net v3] net/mlx5e: macsec: fix use-after-free of metadata_dst on RX SC delete Message-ID: <20260620163028.GW827683@horms.kernel.org> References: <20260618145545.53035-1-doruk@0sec.ai> Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260618145545.53035-1-doruk@0sec.ai> On Thu, Jun 18, 2026 at 04:55:45PM +0200, Doruk Tan Ozturk wrote: > When an offloaded MACsec RX SC is deleted, macsec_del_rxsc_ctx() released > the per-SC metadata_dst with metadata_dst_free(), which calls kfree() > unconditionally and ignores the dst reference count. The RX datapath in > mlx5e_macsec_offload_handle_rx_skb() looks up the SC under rcu_read_lock() > via xa_load() and, while still holding only the RCU read lock, takes a > reference with dst_hold() and attaches the dst to the skb with > skb_dst_set(). > > A reader that has already obtained the rx_sc pointer can therefore race > with the delete path: > > CPU0 (del_rxsc) CPU1 (rx datapath) > -------------- ------------------ > rcu_read_lock(); > rx_sc = xa_load(...)->rx_sc; > xa_erase(...); > metadata_dst_free(rx_sc->md_dst); /* kfree(), ignores refcount */ > dst_hold(&rx_sc->md_dst->dst); /* UAF */ > skb_dst_set(skb, &rx_sc->md_dst->dst); > > metadata_dst_free() frees the object even though the datapath still holds > (or is about to take) a reference, so the subsequent dst_hold() / > skb_dst_set() and the later skb free operate on freed memory. > > Fix the owner side by dropping the reference with dst_release() instead of > freeing unconditionally. dst_release() only schedules the RCU-deferred > dst_destroy() once the reference count reaches zero, so a concurrent reader > that still holds a reference keeps the object alive. > > Dropping the owner reference is not sufficient on its own: once the owner > reference is the last one, dst_release() drops the count to zero and the > destroy is merely RCU-deferred. A racing reader that runs plain dst_hold() > on that already-dead dst gets rcuref_get() == false but dst_hold() only > WARNs and attaches the dying dst to the skb anyway; the later skb free then > calls dst_release() on an object whose destroy is already scheduled, again > a use-after-free. > > Convert the RX datapath to dst_hold_safe(), which returns false (without > warning) when the dst is already dead, and only attach it to the skb when a > reference was successfully taken. When the SC is being deleted the in-flight > packet simply proceeds without the offload metadata_dst: skb_metadata_dst() > returns NULL, the MACsec core sees !is_macsec_md_dst and skips this secy > (rx_uses_md_dst path), which is the correct behaviour for a packet whose SC > is going away. > > While reworking the datapath lookup, also guard the two NULL dereferences > on the same path that an automated review (forwarded by Simon Horman) > flagged: xa_load() can return NULL when the fs_id has just been erased, and > mlx5e_macsec_add_rxsc() publishes sc_xarray_element via xa_alloc() before > rx_sc->md_dst is allocated, so a packet carrying a freshly recycled fs_id > can observe a non-NULL rx_sc whose md_dst is still NULL. Check both before > dereferencing. > > Note: macsec_del_rxsc_ctx() also kfree()s rx_sc->sc_xarray_element without > an RCU grace period while the same datapath reads it under rcu_read_lock(); > that is a separate pre-existing issue and is left to a follow-up patch. > > Fixes: b7c9400cbc48 ("net/mlx5e: Implement MACsec Rx data path using MACsec skb_metadata_dst") > Cc: stable@vger.kernel.org > Signed-off-by: Doruk Tan Ozturk > --- > v3: > - Also guard the RX-datapath NULL dereferences flagged by the automated > review: NULL-check the xa_load() result and rx_sc->md_dst before use. The review of this patch on sashiko.dev flags that this change doesn't appear to be complete: "This is a pre-existing issue, but since xa_alloc() in mlx5e_macsec_add_rxsc() publishes sc_xarray_element before rx_sc->md_dst is allocated and initialized, is it safe to use a plain read here? drivers/net/ethernet/mellanox/mlx5/core/en_accel/macsec.c:mlx5e_macsec_add_rxsc() { ... err = xa_alloc(&macsec->sc_xarray, &sc_xarray_element->fs_id, sc_xarray_element, ...); ... rx_sc->md_dst = metadata_dst_alloc(0, METADATA_MACSEC, GFP_KERNEL); ... } Because there are no memory barriers around the assignment and initialization of md_dst, could a concurrent datapath reader observe a non-NULL md_dst pointer but read uninitialized memory from it in dst_hold_safe()?" ...