From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-172.mta0.migadu.com (out-172.mta0.migadu.com [91.218.175.172]) (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 B1E1418A6DB for ; Wed, 4 Mar 2026 07:43:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772610218; cv=none; b=WDExHl8/Xb6gW85Zm5HchcVSntPx37s1YNAa3EjyMgnsW0ChurykLzH9hXoU2jf9xSHMc0sTiVRRrtQkr8yfOrk04rHAY1b1pUO6UQWnui8wia0iJMBNAAjyNytUx3xj0cY/G08rnc+LrvJl01Ol5ABZ9i6dvhYvqkWFDysivVw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772610218; c=relaxed/simple; bh=ds9fEzCzgnOh8aZtFA8qphSeg7jiatW+uffLqHndLZk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=j2yNUwDclgHARVr3bgKzKFbdqCDSS59l4bLGJy9eu0UE/7mnvRF3RaeTchwVUu9fU2XMeATSrp/DTetp2La27V4Yy8nhrGlJuaiCmxlJiF4cuLwoWk+JMhQOQ55KGaZvz3e96HXPgeA+UnyKE45Inj4oMcsBYfSqlbN58HQfM0Y= 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=hPttfdbf; arc=none smtp.client-ip=91.218.175.172 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="hPttfdbf" 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=1772610214; 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: in-reply-to:in-reply-to:references:references; bh=gkKYESAH5YFAD03Jj76NpTW6HeKRoN5KgHV8fqdKUwk=; b=hPttfdbfoMJn5mkbkpzGib/ixwWVH0nVRqwVGlyIaVXN9oRVzmBs5c5HBelUUTKaec9iba Z4Jz4Xq/vaUOzJG9K2wyfuWbtmATt2rQlm63ShEphIYdfmjN+vIRmhWudq7wFzXodtx9iD 4n9V8PUb0fIoIDas7XPnB0O36Oqu4Hg= From: Jiayuan Chen To: jv@jvosburgh.net, netdev@vger.kernel.org Cc: jiayuan.chen@linux.dev, jiayuan.chen@shopee.com, syzbot+80e046b8da2820b6ba73@syzkaller.appspotmail.com, Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Hao Luo , Jiri Olsa , Shuah Khan , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , Jussi Maki , linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-rt-devel@lists.linux.dev Subject: [PATCH net v4 1/2] bonding: fix null-ptr-deref in bond_rr_gen_slave_id() Date: Wed, 4 Mar 2026 15:42:57 +0800 Message-ID: <20260304074301.35482-2-jiayuan.chen@linux.dev> In-Reply-To: <20260304074301.35482-1-jiayuan.chen@linux.dev> References: <20260304074301.35482-1-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 bond_rr_gen_slave_id() dereferences bond->rr_tx_counter without a NULL check. rr_tx_counter is a per-CPU counter only allocated in bond_open() when the bond mode is round-robin. If the bond device was never brought up, rr_tx_counter remains NULL, causing a null-ptr-deref. The XDP redirect path can reach this code even when the bond is not up: bpf_master_redirect_enabled_key is a global static key, so when any bond device has native XDP attached, the XDP_TX -> xdp_master_redirect() interception is enabled for all bond slaves system-wide. This allows the path xdp_master_redirect() -> bond_xdp_get_xmit_slave() -> bond_xdp_xmit_roundrobin_slave_get() -> bond_rr_gen_slave_id() to be reached on a bond that was never opened. Fix this by allocating rr_tx_counter unconditionally in bond_init() (ndo_init), which is called by register_netdevice() and covers both device creation paths (bond_create() and bond_newlink()). This also handles the case where bond mode is changed to round-robin after device creation. The conditional allocation in bond_open() is removed. Since bond_destructor() already unconditionally calls free_percpu(bond->rr_tx_counter), the lifecycle is clean: allocate at ndo_init, free at destructor. Note: rr_tx_counter is only used by round-robin mode, so this deliberately allocates a per-cpu u32 that goes unused for other modes. Conditional allocation (e.g., in bond_option_mode_set) was considered but rejected: the XDP path can race with mode changes on a downed bond, and adding memory barriers to the XDP hot path is not justified for saving 4 bytes per CPU. Fixes: 879af96ffd72 ("net, core: Add support for XDP redirection to slave device") Reported-by: syzbot+80e046b8da2820b6ba73@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/698f84c6.a70a0220.2c38d7.00cc.GAE@google.com/T/ Signed-off-by: Jiayuan Chen --- drivers/net/bonding/bond_main.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c index 78cff904cdc3..55b5c7a6cb5f 100644 --- a/drivers/net/bonding/bond_main.c +++ b/drivers/net/bonding/bond_main.c @@ -4279,12 +4279,6 @@ static int bond_open(struct net_device *bond_dev) struct list_head *iter; struct slave *slave; - if (BOND_MODE(bond) == BOND_MODE_ROUNDROBIN && !bond->rr_tx_counter) { - bond->rr_tx_counter = alloc_percpu(u32); - if (!bond->rr_tx_counter) - return -ENOMEM; - } - /* reset slave->backup and slave->inactive */ if (bond_has_slaves(bond)) { bond_for_each_slave(bond, slave, iter) { @@ -6411,6 +6405,19 @@ static int bond_init(struct net_device *bond_dev) if (!bond->wq) return -ENOMEM; + /* rr_tx_counter is only used in round-robin mode, but we allocate + * it unconditionally because the XDP redirect path + * (xdp_master_redirect -> bond_xdp_get_xmit_slave) can reach here + * even when the bond is not up, and deferring allocation to + * bond_open or bond_option_mode_set would require memory barriers + * on the XDP hot path. The cost is a per-cpu u32 per bond device. + */ + bond->rr_tx_counter = alloc_percpu(u32); + if (!bond->rr_tx_counter) { + destroy_workqueue(bond->wq); + return -ENOMEM; + } + bond->notifier_ctx = false; spin_lock_init(&bond->stats_lock); -- 2.43.0