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 CA30247D93C for ; Wed, 5 Aug 2026 16:43:37 +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=1785948218; cv=none; b=Pg8cc+jYoPiWKCP1sUyA5AX+LXxBM9oq8GGsYJOy1SeVMwvuss5fkFodD1t1h5f735oeCO8GZNMMJ5xQiJnj6rHdGuHvh4EtoYlWfkQN6F4aKiJDeLryRHpcJve5g3WgA96/JIhWGk/00BVJQIiPXIWH2EYyol//U/gc1sPidf8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785948218; c=relaxed/simple; bh=m+DaYMTzRvYL1ZbMsRCuthE2sPGFkPySK7Vb4Myiq7I=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=FEiwhkqLUBmKNHrup9cczwPjIaHAAKrDAwbfdAUNy/99/FYqAm4upWoWFplPU4SmdIXAR5jfxh2WXjLo+SNMJtNK4/fo03ou1PBiAIkHKTYlfmQ/YDYEj99iCWKeQvPedxH7c6gKbSdgF9JPIywGlEOy/QWURrdmXhFDlyDgFlA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=K5XWbCcl; 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="K5XWbCcl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5C1871F00A3A for ; Wed, 5 Aug 2026 16:43:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785948217; bh=QShTgui7c8EIeqUFSSvHCLazN79sqJhph1q6frDc8Fg=; h=Date:Subject:To:References:From:In-Reply-To; b=K5XWbCcluVbHAAex8fJYch12lMU1xei6fluFvJW+7FTuBZjDBh5BnGKpy96bjLFqK 2omo2KeYqkcsrE5xAtUlGYlXQ0D8OXRcdR43j+s5YiT2LNm1cQ5919RPQWMLOaBZYj zC5PHCoxy1t+g3bAAHkFvacBDPDCSjTNQ0H69RhtlgFSwGtFUTz9t8fiSl0p/qoFxo 0/Cnl+Dof/jVN5CyvIV9+NQqmzpceoy+kbg1hINB+Vv3PVwEzb2V/GhHcTE7fi8NbR aHtrarj78STxV3j0vgKqlTByWVJDG+119vZ5wV8G6BkM33qsincInQA1OUcfP9+OKK /7Grp3FuAmk1A== Message-ID: Date: Wed, 5 Aug 2026 18:43:36 +0200 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH mptcp-net 3/6] mptcp: pm: userspace: no ID0 exception for RM_ADDR Content-Language: fr To: MPTCP Linux References: <20260727-mptcp-pm-userspace-id0-case-v1-0-9877f02a9bae@kernel.org> <20260727-mptcp-pm-userspace-id0-case-v1-3-9877f02a9bae@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Replying to Sashiko's review: >> After the first patch of this series, the initial ID0 address is present >> in the local addr list when the connection has been created. > > Does adding the initial ID 0 address to the local address list cause > secondary subflow creation to fail for incoming joins on unannounced > addresses? > > When a secondary subflow is initiated using a new address with ID 0, > mptcp_userspace_pm_append_new_local_addr() loops over the list. > > The new entry will match the ID 0 of the initial address (id_match = true) > but its IP differs (addr_match = false). > > This causes the loop to break, bypassing allocation and ID assignment, > and returns -EINVAL. Same comment as on patch 1/6. > Does destroying the initial subflow (ID 0) via userspace PM cause an > underflow of msk->pm.local_addr_used? > > If the initial ID 0 connection address is added without incrementing > the local_addr_used counter, later calling MPTCP_PM_CMD_SUBFLOW_DESTROY > on ID 0 will unconditionally decrement it in > mptcp_userspace_pm_delete_local_addr(). > > Could this wrap the 8-bit counter to 255 and corrupt the statistics > exported to userspace? Same comment as on patch 1/6. >> diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c >> index 4c96433590e36..9c7fab6a59bf4 100644 >> --- a/net/mptcp/pm_userspace.c >> +++ b/net/mptcp/pm_userspace.c > > [ ... ] > >> @@ -315,11 +284,6 @@ int mptcp_pm_nl_remove_doit(struct sk_buff *skb, struct genl_info *info) >> >> sk = (struct sock *)msk; >> >> - if (id_val == 0) { >> - err = mptcp_userspace_pm_remove_id_zero_address(msk); >> - goto out; >> - } >> - >> lock_sock(sk); >> >> spin_lock_bh(&msk->pm.lock); > > This is a pre-existing issue, but does decrementing sk_omem_alloc eagerly > while freeing memory via RCU allow a local user in a user namespace to > bypass socket memory limits? > > Later in mptcp_pm_nl_remove_doit(): > > kfree_rcu_mightsleep(match); > /* Adjust sk_omem_alloc like sock_kfree_s() does, to match > * with allocation of this memory by sock_kmemdup() > */ > atomic_sub(sizeof(*match), &sk->sk_omem_alloc); > > If a user with CAP_NET_ADMIN repeatedly announces and removes addresses in > a tight loop via MPTCP_PM_CMD_ANNOUNCE and MPTCP_PM_CMD_REMOVE, the > sk_omem_alloc counter is decremented immediately, but the actual freeing > is deferred to RCU grace periods. > > Could this potentially lead to memory exhaustion (OOM) on the host? Mmh, I don't think we need to handle this case with CAP_NET_ADMIN, plus the netlink communication will not allow too many loops I suppose. (+ pre-existing issue: for a follow-up patch anyway) Cheers, Matt -- Sponsored by the NGI0 Core fund.