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 9D6CE49DBBF for ; Wed, 16 Sep 2026 12:39:58 +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=1789562399; cv=none; b=A70aiuLBCVLnwFeGh1Zd9m4NuZgoSaKI+GK5c9ovKHQpqhujbeD7StaTx0wowdNUIINEJ5r5mEbzKZCkpiBYOTOn0/ObZepmHVTgBsg/MlWWjOcN77JvmyJjOGiVKCLo8TIt05DJoq/KL+QcruRmdxPKTOilbfnZSdzsdWwTBj0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789562399; c=relaxed/simple; bh=obbFqjsqQURuuAHQWNSkuAlWX86upgongf34c6qMYbI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=LVNT1SJjXpnrsFakOANCKsOzO9wGJYUztOMYPHNQNK+51ceyrZ0thWqRUaDD/nRS4OgTgwl+8NuQVVH5mXLeru5Wr0f6aYAvErKYuy3m8kuWe2AuVW+4oqiAAt+/EHMAJDpqk0fc1bDSktrNQPUlMt//wIVBRfIwLCk6HMyluIQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EJiT8+XG; 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="EJiT8+XG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6461B1F000FF; Wed, 16 Sep 2026 12:39:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789562398; bh=rWVOzU/2+C0cR+TBJ0RERl5URTwYNBV6yjGd33DBYv8=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=EJiT8+XGPZBLvzp69vVOdVafxFunskKAyqg8MjiTWCwvZqnMkY20CewqIa9ge1SwT SRtACzrbqwq7o57C9/SNMIylRQsqh0esYf78tnP9ftbBtgP1hOomaxEUW0LMvlKnz2 A3ucx0o2ZYOXTw0rR7Yf11cE/y6S6QF+0ppXF6P42jbhfJi3dLn62bN+AygWv8pome VmsDVxyYsiLSV1JE61XpoHR4Vdqn/7YSWQDKYu1ATiny620WLml3fovC7Gw//p3OOy Ma1VPaMoQnTQa0xYekKLBXQ9/jHEmNj7Cl3ZaZUemECbEka3NquYaWkimmM/gWT7Ox qsuXGWx59BBCA== Date: Wed, 16 Sep 2026 13:39:54 +0100 From: Simon Horman To: Eric Dumazet Cc: "David S. Miller" , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, eric.dumazet@gmail.com, Jungwoo Lee , Wongi Lee Subject: Re: [PATCH net] net: lock the socket in sock_gettstamp() Message-ID: <20260916123954.GF51261@horms.kernel.org> References: <20260915043055.3441600-1-edumazet@google.com> Precedence: bulk X-Mailing-List: netdev@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: <20260915043055.3441600-1-edumazet@google.com> On Tue, Sep 15, 2026 at 04:30:54AM +0000, Eric Dumazet wrote: > sk->sk_flags must only be changed while holding the socket lock, > because sock_set_flag() and sock_reset_flag() use non atomic > operations (__set_bit() and __clear_bit()). > > sock_gettstamp() is one of the last places where a bit of sk->sk_flags > is changed from a syscall without owning the socket lock, through > sock_enable_timestamp(sk, SOCK_TIMESTAMP). > > sk_set_memalloc() and sk_clear_memalloc() also change sk->sk_flags > without the socket lock, but their callers (nbd, iscsi_tcp, nvme-tcp, > sunrpc, wireguard) need a careful audit, this will be addressed in a > separate patch. > > Jungwoo Lee and Wongi Lee reported an UDP socket use-after-free > caused by this bug: a SIOCGSTAMPNS_NEW ioctl racing with bind() > can cancel the SOCK_RCU_FREE bit that udp_lib_get_port() just set, > because both threads perform a read-modify-write on the same word. > > CPU 0 (bind) CPU 1 (SIOCGSTAMPNS_NEW) > -------------------------------- ---------------------------- > read sk_flags = F read sk_flags = F > compute F | BIT(SOCK_RCU_FREE) compute F | BIT(SOCK_TIMESTAMP) > store F | BIT(SOCK_RCU_FREE) > sk_add_node_rcu(sk, ...) > store F | BIT(SOCK_TIMESTAMP) > > After the lost update, SOCK_RCU_FREE is clear while the socket is > visible to lockless UDP receive lookups. sk_destruct() then frees > the socket immediately instead of waiting for a RCU grace period, > while the receive path still holds a reference-less pointer to it: > > BUG: KASAN: slab-use-after-free in ipv4_pktinfo_prepare+0x30/0x410 > Read of size 8 at addr ffff888008806610 by task exploit/207 > CPU: 0 UID: 1000 PID: 207 Comm: exploit Not tainted 6.12.95+ #1 > ipv4_pktinfo_prepare+0x30/0x410 > udp_queue_rcv_one_skb+0x51c/0x1180 > udp_unicast_rcv_skb+0x109/0x350 > ip_protocol_deliver_rcu+0x14b/0x310 > ip_local_deliver_finish+0x29d/0x390 > ip_local_deliver+0x24d/0x2a0 > > Only grab the socket lock when SOCK_TIMESTAMP has to be set, > to keep the common case lockless. > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Reported-by: Jungwoo Lee > Reported-by: Wongi Lee > Signed-off-by: Eric Dumazet Reviewed-by: Simon Horman