From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-187.mta1.migadu.com (out-187.mta1.migadu.com [95.215.58.187]) (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 3E40B39DBC1 for ; Fri, 10 Apr 2026 11:38:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.187 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775821083; cv=none; b=QEFuudN8QxQ8u5bpeshM2M/imIELwTwGFtn2MfMLULE82CXFcUd3jns563fCvQJZu5qiB4cvNCaOmhHouPNuUenHzK5uqerg6JURSlUTxTtf1KCjw96uuErTNbL7fnS8OKS0tVUcJW+rBZOlOQeR51yNXwZ7O4kd+b0oyqT70nI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775821083; c=relaxed/simple; bh=1dX4uXwGzRHChAqZIKUJnts7+cVmhDPfr4wixNUYVkk=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=CN/W/++o8WKFWFMa1u4CRIR9PaqycF2CWmeUuoCfIdeWN6o4Z0XZSIjBP4pCR+xoTWRKUWFZEarigcEjNuhb5FIZK1homha3dDmelBd23AGoiPM9/jcH5FDllehjvwqFX380BIvHThQFilpNWiI80ZhaBCg1veXMlcUz0zB4674= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=U+wMO9WA; arc=none smtp.client-ip=95.215.58.187 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="U+wMO9WA" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1775821070; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=KeqZvV+Oy9FQiiKRUD3VowmUdxbmTHkCnn/4hwZRALo=; b=U+wMO9WATDP9BfWiPwhR7iA5Nd5PfmBagdYVXBnjUUg5GTlNgvvs9+8klD9yhrYRFER/Qv mjvMWlD3UrS3t4CNun37TbB3HwUNtfJ+dV6dnknl7ayAxNv/87zDo/BjN8XJipQLYeFC3a TzXfV6JdAz6fbfqxBWEZvyY1sPe8K+Y= From: Jiayuan Chen To: netdev@vger.kernel.org Cc: Jiayuan Chen , Martin KaFai Lau , Daniel Borkmann , John Fastabend , Stanislav Fomichev , Alexei Starovoitov , Andrii Nakryiko , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Hao Luo , Jiri Olsa , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jesper Dangaard Brouer , Shuah Khan , Jussi Maki , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH net v6 0/2] net,bpf: fix null-ptr-deref in xdp_master_redirect() for bonding and add selftest Date: Fri, 10 Apr 2026 19:37:21 +0800 Message-ID: <20260410113726.368111-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT From: Jiayuan Chen This series has gone through several rounds of discussion and the maintainers hold different views on where the fix should live (in the generic xdp_master_redirect() path vs. inside bonding). I respect all of the suggestions, but I would like to get the crash fixed first, so this version takes the approach of checking whether the master device is up in xdp_master_redirect(), as suggested by Daniel Borkmann. If a different shape is preferred later it can be done as a follow-up, but the null-ptr-deref should not linger. syzkaller reported a kernel panic, full decoded trace here: https://syzkaller.appspot.com/bug?extid=80e046b8da2820b6ba73 Problem Description bond_rr_gen_slave_id() dereferences bond->rr_tx_counter without a NULL check. rr_tx_counter is a per-CPU counter that bonding only allocates in bond_open() when the mode is round-robin. If the bond device was never brought up, rr_tx_counter stays NULL. The XDP redirect path can still reach that code on a bond that was never opened: bpf_master_redirect_enabled_key is a global static key, so as soon as any bond device has native XDP attached, the XDP_TX -> xdp_master_redirect() interception is enabled for every slave system-wide. The path xdp_master_redirect() -> bond_xdp_get_xmit_slave() -> bond_xdp_xmit_roundrobin_slave_get() -> bond_rr_gen_slave_id() then runs against a bond that has no rr_tx_counter and crashes. Solution Patch 1: Fix this in the generic xdp_master_redirect() by skipping master interception when the master device is not running. Returning XDP_TX keeps the original XDP_TX behaviour on the receiving slave, and avoids calling into any master ->ndo_xdp_get_xmit_slave() on a device that has not fully initialized its XDP state. This is not specific to bonding: any current or future master that defers XDP state allocation to ->ndo_open() is protected. Patch 2: Add a selftest that reproduces the above scenario. Changes since v5: https://lore.kernel.org/netdev/20260309030659.xxxxx-1-jiayuan.chen@linux.dev/ - Moved the fix back into xdp_master_redirect() and use netif_running() on the master device to decide whether to intercept (Suggested by Daniel Borkmann, seconded by Paolo Abeni and Eric Dumazet) Changes since v4: https://lore.kernel.org/netdev/20260304074301.35482-1-jiayuan.chen@linux.dev/ - Reverted unconditional alloc in bond_init(); instead add a NULL check with unlikely()/READ_ONCE() in bond_rr_gen_slave_id() and WRITE_ONCE() in bond_open(), avoiding memory waste for non-RR modes (Suggested by Nikolay Aleksandrov, patch by Jay Vosburgh) Changes since v3: https://lore.kernel.org/netdev/20260228021918.141002-1-jiayuan.chen@linux.dev/T/#t - Added code comment and commit log explaining why rr_tx_counter is allocated unconditionally for all modes (Suggested by Jay Vosburgh) Changes since v2: https://lore.kernel.org/netdev/20260227092254.272603-1-jiayuan.chen@linux.dev/T/#t - Moved allocation from bond_create_init() helper into bond_init() (ndo_init), which is the natural single point covering both creation paths and also handles post-creation mode changes to round-robin Changes since v1: https://lore.kernel.org/netdev/20260224112545.37888-1-jiayuan.chen@linux.dev/T/#t - Moved the guard for NULL rr_tx_counter from xdp_master_redirect() into the bonding subsystem itself (Suggested by Sebastian Andrzej Siewior ) [1] https://syzkaller.appspot.com/bug?extid=80e046b8da2820b6ba73 Jiayuan Chen (2): net, bpf: fix null-ptr-deref in xdp_master_redirect() for down master selftests/bpf: add test for xdp_master_redirect with bond not up net/core/filter.c | 2 + .../selftests/bpf/prog_tests/xdp_bonding.c | 101 +++++++++++++++++- 2 files changed, 101 insertions(+), 2 deletions(-) -- 2.43.0