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 27DE33AFCFF; Thu, 20 Aug 2026 06:55:06 +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=1787208908; cv=none; b=Pi5J32N6s3q39Qqqu9jppGv2hqFdX2PZhT30aQpXz6c1T9EPAINMd1Td/fLbqezJEwpnazKQFstsdmz2sd0TZKsZG1CGlHdwH12zC27BmNxiiwvSKstd513RrM5FUnRdSE+1avA0ifLX0t28ZAR2Lt3dgGvJAdFfJCE1lWULZJw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787208908; c=relaxed/simple; bh=wEFxQa5SNPReRNjDvbiJj8OYcP1WF4n28NrwoohbF+k=; h=From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type:Date; b=ljMLU4abeOBLqvhWT+YftAKIcRfELyvQIK4qciSiU0XFwEuccn22nPtVN+D9R2v9cRNsT1wTc/z/Jpq/xU5U8NVpxSUeuAsDm2b9CsYi0KO+l/kYxgvU5JEP85e6pzAD2tzn0WR4Nkc83CDPzHYEAS4I4bugMkpQb5oT/weeTP8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=URW1o/2R; 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="URW1o/2R" Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id 1D0EC1F000E9; Thu, 20 Aug 2026 06:55:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787208906; bh=gJY0VXS+RATQ0tFGGr3u0BU3d0wxy1hBz4D31aEOs2Y=; h=From:To:Cc:Subject:Date; b=URW1o/2RzMzQ9Wj98j5kwVQLlEorAviuHYq1HKKs1RkYge/0A6pxB7Ypas/V0Kx86 c2SW7s9pTg2bVgBbCgVpbU2/hyicbQIRq/QFCsk4ZL7MlUbwsfOnAYCMPfMOsdPD7o DsndY+1E6Kq0fpkThCiuTl4gmaeNt//EjNzDyzNSIMAA84MWABwRKARC5HNKLgsohp /FqU/9nzwzfuDleOdk8UERnNNUp5jMj/TenHbeJrhcXPYmRP7Qg5qz42MHNXl6gxrq TuknOPnoZIQj8Qy2JB8ZpRlejxL/JuTI+Od4P/u1+kioXRKxyKFaL6Cx/6p6rwPEA7 p9+XXo3heXmrQ== From: "syzbot" To: syzkaller-bugs@googlegroups.com, Slawomir Stepien , "Chuck Lever" , "Jeff Layton" , , "Lorenzo Bianconi" Cc: Dai.Ngo@oracle.com, linux-kernel@vger.kernel.org, neil@brown.name, okorniev@redhat.com, syzbot@lists.linux.dev, tom@talpey.com Subject: [PATCH] nfsd: prevent hung task in nfsd_nl_listener_set_doit() Message-ID: <4601ffd5-c662-4ab1-ab2f-50a67a0a990e@mail.kernel.org> Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Date: Thu, 20 Aug 2026 06:55:06 +0000 (UTC) From: Slawomir Stepien In nfsd_nl_listener_set_doit(), the kernel iterates over all NFSD_A_SERVER_SOCK_ADDR attributes provided in a netlink message to configure NFS server listeners. There is currently no limit on the number of attributes a user can send. For each attribute, svc_xprt_create_from_sa() is called, which may synchronously invoke request_module() to load the corresponding transport module. If a user provides a large number of invalid transport names, request_module() is called sequentially for each, taking a massive amount of time. Since this entire process occurs while holding the global nfsd_mutex, it blocks other tasks attempting to acquire the mutex and triggers a hung task timeout: INFO: task blocked for more than 10 seconds. ... Call Trace: __schedule+0x17e7/0x5630 kernel/sched/core.c:7234 schedule+0x164/0x2b0 kernel/sched/core.c:7326 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7383 __mutex_lock_common kernel/locking/mutex.c:726 [inline] __mutex_lock+0x7bf/0x1550 kernel/locking/mutex.c:821 nfsd_nl_version_get_doit+0x17c/0xd20 fs/nfsd/nfsctl.c:1889 genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114 genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline] genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209 ... 2 locks held by task/5864: #0: ffffffff90114168 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217 #1: ffffffff8eeb1a60 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_listener_set_doit+0x135/0x1750 fs/nfsd/nfsctl.c:1964 Furthermore, the function does not break out of the loop if svc_xprt_create_from_sa() fails, and it suffers from an O(N^2) complexity issue because svc_find_listener() iterates over the serv->sv_permsocks list for each attribute. Address this by introducing a hard limit of 128 NFSD_A_SERVER_SOCK_ADDR attributes per netlink message. The limit is enforced before acquiring the nfsd_mutex to prevent lock contention. Additionally, modify the loop to break immediately if listener creation fails, avoiding needless sequential request_module() calls for invalid configurations. Fixes: 16a471177496 ("NFSD: add listener-{set,get} netlink command") Assisted-by: Gemini:gemini-3.6-flash Gemini:gemini-3.1-pro-preview syzbot Reported-by: syzbot+41bc60511c2884783c27@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=41bc60511c2884783c27 Link: https://syzkaller.appspot.com/ai_job?id=30871f87-7a83-46b8-ab83-919894b0787b Signed-off-by: Slawomir Stepien --- diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c index fa92e31d1..516c04c14 100644 --- a/fs/nfsd/nfsctl.c +++ b/fs/nfsd/nfsctl.c @@ -1943,6 +1943,8 @@ int nfsd_nl_version_get_doit(struct sk_buff *skb, struct genl_info *info) return err; } +#define NFSD_MAX_LISTENERS 128 + /** * nfsd_nl_listener_set_doit - set the nfs running sockets * @skb: reply buffer @@ -1955,12 +1957,19 @@ int nfsd_nl_listener_set_doit(struct sk_buff *skb, struct genl_info *info) struct net *net = genl_info_net(info); struct svc_xprt *xprt, *tmp; const struct nlattr *attr; + unsigned int count = 0; struct svc_serv *serv; LIST_HEAD(permsocks); struct nfsd_net *nn; bool delete = false; int err, rem; + nlmsg_for_each_attr_type(attr, NFSD_A_SERVER_SOCK_ADDR, info->nlhdr, + GENL_HDRLEN, rem) { + if (++count > NFSD_MAX_LISTENERS) + return -EINVAL; + } + mutex_lock(&nfsd_mutex); err = nfsd_create_serv(net); @@ -2073,8 +2082,10 @@ int nfsd_nl_listener_set_doit(struct sk_buff *skb, struct genl_info *info) ret = svc_xprt_create_from_sa(serv, xcl_name, net, sa, 0, current_cred()); /* always save the latest error */ - if (ret < 0) + if (ret < 0) { err = ret; + break; + } } if (!serv->sv_nrthreads && list_empty(&nn->nfsd_serv->sv_permsocks)) base-commit: 075b74841bd0065a3bda3440873c747938e69b68 -- See https://goo.gle/syzbot-ai-patches for information about AI-generated patches. The person who has signed off on the patch is responsible for addressing comments. syzbot engineers can be reached at syzkaller@googlegroups.com.