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 DF463423EAB; Mon, 17 Aug 2026 13:06:12 +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=1786971974; cv=none; b=o3n0mN/9Ij1qieDuWauF5fdcURFslNAU/cX12sujItetQ9mHzbz1CMTXFE2bbG0xFxkxX5HHx29JRICKWGG3dFmdjoGDqw6xxvUaJ+bR7zqr9RqrHKTTZlVlBZ3wrRp+SggiwZQwzJnBE5/JPWwXyEr3MtoQHOLwAUsDkZTRidU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786971974; c=relaxed/simple; bh=tajMC1o2lJbEnAvJo9cu6ifNA4M2SO31OrAW3DNdXaw=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=T+Jg8zb0C6wtTPUy8a6cltHsKFKlO5QlZ7Widgjv3U27kJuarsJVN/9kAymDE7EGektYVVNahl4LG2fYyjs6ooNLSxel1HF7DkTYrPRy+snoWwbPqS/Q9gkh8agrvIr1+fwWX+tNJOjAAOFWrdseR3LMNBtoxNzQ84q7NzI6P2Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MFknYHRC; 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="MFknYHRC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 163F91F000E9; Mon, 17 Aug 2026 13:06:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786971972; bh=hKGpUIrNxodDsOVoJv1RPOzms6R0bvYfWxFdg1zmg1w=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=MFknYHRC0TzJV7a1UXP95tGSTOcGC7RLsU+OwMTjxv5RyR+HTg+3UrhH4+MQtvilr xTc6u5fLWUYxMGEcvasEjjlGP8nfRtWHT5uOIw/2U1TiJSOgtz7ZUBJWKbw3LPPiuC AxAcItBQE9q8TUpzE4X2IFPBGVngLfFJweOef6EtCgvfwOyX18ABOzwR9BzaGsAaQA m3tJ3oWzXM8YMZ7JOugnY4uHogduTAW2X1j9JcaYo2N1Hfww937rhZpbiZk0L2MmBT aqNlVp9+wMqurOp6q3YRRml5z6F7ydbwUdoTcl5CF1I0kjLkhTSqwmmR4hopHxZyWn 5GEdTc2i7GZ/Q== Message-ID: <9223c486ff90585a56556d810901c2cbcec85bae.camel@kernel.org> Subject: Re: [PATCH v1] SUNRPC: Reject a socket that already has an svc_sock attached From: Jeff Layton To: Chuck Lever , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, syzbot+54cdc566f64abf51b7f1@syzkaller.appspotmail.com Date: Mon, 17 Aug 2026 09:06:10 -0400 In-Reply-To: <20260815162844.8219-1-cel@kernel.org> References: <20260815162844.8219-1-cel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Sat, 2026-08-15 at 12:28 -0400, Chuck Lever wrote: > Writing the same socket descriptor to /proc/fs/nfsd/portlist twice > attaches a second svc_sock to one socket. svc_setup_socket() saves > the socket's callbacks before installing its own, so the second > attach records svc_write_space() as the old write_space callback. > svc_udp_init() invokes that callback by way of svc_sock_setbufsize(), > and svc_write_space() then calls itself until the kernel stack is > exhausted: >=20 > BUG: TASK stack guard page was hit at ffffc900037d7ff8 > svc_write_space+0x90/0x2b0 net/sunrpc/svcsock.c:429 > svc_write_space+0xe6/0x2b0 net/sunrpc/svcsock.c:430 > ... 700 more ... > svc_sock_setbufsize+0x18d/0x220 net/sunrpc/svcsock.c:386 > svc_udp_init net/sunrpc/svcsock.c:854 [inline] > svc_setup_socket+0xb2f/0x1090 net/sunrpc/svcsock.c:1498 > svc_addsock+0x2fd/0x760 net/sunrpc/svcsock.c:1547 > __write_ports_addfd fs/nfsd/nfsctl.c:742 [inline] > write_ports+0xa5b/0xcc0 fs/nfsd/nfsctl.c:861 > nfsctl_transaction_write+0x106/0x1a0 fs/nfsd/nfsctl.c:112 >=20 > svc_data_ready() and svc_tcp_state_change() chain through their saved > callbacks the same way, so a TCP descriptor added twice recurses on > the next incoming segment instead. Reaching any of this takes a > writer on portlist, and the nfsd filesystem sets no FS_USERNS_MOUNT, > so the reproducer needs CAP_SYS_ADMIN in the initial user namespace. >=20 > Reject a socket that already carries sk_user_data. svc_setup_socket() > overwrites that field unconditionally, so a socket some other > consumer has claimed is one NFSD would corrupt whether or not the > callbacks recurse. >=20 > Fixes: b41b66d63c73 ("[PATCH] knfsd: allow sockets to be passed to nfsd v= ia 'portlist'") > Reported-by: syzbot+54cdc566f64abf51b7f1@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=3D54cdc566f64abf51b7f1 > Signed-off-by: Chuck Lever > --- > net/sunrpc/svcsock.c | 3 +++ > 1 file changed, 3 insertions(+) >=20 > diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c > index 7a423e9ee74d..5a2d52284d75 100644 > --- a/net/sunrpc/svcsock.c > +++ b/net/sunrpc/svcsock.c > @@ -1614,6 +1614,9 @@ int svc_addsock(struct svc_serv *serv, struct net *= net, const int fd, > err =3D -EISCONN; > if (so->state > SS_UNCONNECTED) > goto out; > + err =3D -EBUSY; > + if (so->sk->sk_user_data) > + goto out; > err =3D -ENOENT; > if (!try_module_get(THIS_MODULE)) > goto out; Nice catch! Reviewed-by: Jeff Layton Claude had some pedantry about the changelog though. Regurgitated verbatim here: > svc_data_ready() and svc_tcp_state_change() chain through their saved > callbacks the same way, so a TCP descriptor added twice recurses on > the next incoming segment instead. Are those the two callbacks that recurse for tcp? The write_ports kerneldoc says "listen(3) must be called for a SOCK_STREAM socket", and for a listening socket svc_tcp_init() only replaces sk_data_ready: net/sunrpc/svcsock.c:svc_tcp_init() { ... if (sk->sk_state =3D=3D TCP_LISTEN) { strcpy(svsk->sk_xprt.xpt_remotebuf, "listener"); set_bit(XPT_LISTENER, &svsk->sk_xprt.xpt_flags); set_bit(XPT_RPCB_UNREG, &svsk->sk_xprt.xpt_flags); sk->sk_data_ready =3D svc_tcp_listen_data_ready; set_bit(XPT_CONN, &svsk->sk_xprt.xpt_flags); } else { sk->sk_state_change =3D svc_tcp_state_change; sk->sk_data_ready =3D svc_data_ready; sk->sk_write_space =3D svc_write_space; ... } sk_state_change and sk_write_space are left alone on a listener, so the second svc_setup_socket() saves svc_tcp_listen_data_ready() into sk_odata and the recursion runs there instead: net/sunrpc/svcsock.c:svc_tcp_listen_data_ready() { struct svc_sock *svsk =3D (struct svc_sock *)sk- >sk_user_data; ... if (svsk) { /* Refer to svc_setup_socket() for details. */ rmb(); svsk->sk_odata(sk); ... } The else branch does install svc_data_ready() and svc_tcp_state_change(), but svc_addsock() only reaches it for a descriptor that is not listening, and svc_tcp_init() then closes that transport right away: net/sunrpc/svcsock.c:svc_tcp_init() { ... switch (sk->sk_state) { case TCP_SYN_RECV: case TCP_ESTABLISHED: break; default: svc_xprt_deferred_close(&svsk->sk_xprt); } ... } Should the paragraph name svc_tcp_listen_data_ready() instead?