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 86ADE357D0B; Sun, 18 Oct 2026 12:04:40 +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=1792325081; cv=none; b=kNyz0HB4t8SWWnYJkukWqX4dWfiwCF9QXxmm3ZWmkQkE8mFgCE7HIDMZa8UftzfNp+QDZtRb8YrGGRn6v4VjKnQjLg1EaArqw07mrEYEM5UjVA/Hz4SAga3t05u0aAdYOzK6uJfcfoY/i6qR0G8+zkZX7nkc2CPdQSgGkLG8XTM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792325081; c=relaxed/simple; bh=4VAJDO1/CKJVI0ebANtI32wdykDV4hQc/6PffrfFkgE=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=dkDMjjnvSiImH0DolMq1bzf/yvhIRi1itflhon8qO3RRXh/dqz49vSJSQnP71SwENACQt+x5wXZLpZEziIwc2fww0IH/9fRJRbv/d7HF3nVlVd2WaSiV3owr9zrQP9pKjKD/8lYAiZ4xSt6f72DOBtci+L/3bMLqyEhODJVyitg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LFBREco/; 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="LFBREco/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 526621F000C4; Sun, 18 Oct 2026 12:04:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792325080; bh=ocaryIgfW1h4qLGkaFbhHKE0AUKReSaSZC36fkex5No=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=LFBREco/QnVr7xhPsswgt85w1CSMboEzBQLWnWZbEvD7HTEx4unFKJT3nue6PkZ0Q 5qr/REZ6EzqCS9BqWJvQm/7SzmFhHULhp1skK4/7+3GlA9MVjRROn8K/Kh2IxtE+mG XE4eJrNAYu5XxQP2qf8jd8Ezxib9Lu8hLPNiYi0jgCPodkcXt8Fa0N00haXmwqoUyS uXEg4+r3PdCtwbM5jJ/JSWuvphHjdtDiM+9Ks+V9jXaD7zV2uy8KadLIaVhqhEtkiC awR2QkcZB0DtTX42oCCsiizmZoMXQF0Y7PoXYAq9HyIVCE0nWf9ErUyrOPEmkIFwc5 a5P6XVrLbvlbA== Message-ID: Subject: Re: [PATCH] nfsd: fix out-of-bounds read of sv_permsocks when starting a thread From: Jeff Layton To: Deepanshu Kartikey , cel@kernel.org, neil@brown.name, okorniev@redhat.com, Dai.Ngo@oracle.com, tom@talpey.com Cc: bfields@fieldses.org, skinsbursky@parallels.com, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+561b859d032c8bf2fb53@syzkaller.appspotmail.com Date: Sun, 18 Oct 2026 08:04:37 -0400 In-Reply-To: <20261018113312.10455-1-kartikey406@gmail.com> References: <20261018113312.10455-1-kartikey406@gmail.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Sun, 2026-10-18 at 17:03 +0530, Deepanshu Kartikey wrote: > nfsd() derives its struct net from the first entry of > serv->sv_permsocks using list_entry() without checking that the list > is non-empty. If the list is empty, list_entry() returns a bogus > svc_xprt computed from the list head embedded in struct svc_serv, and > the following perm_sock->xpt_net load reads far past the end of the > svc_serv allocation: >=20 > BUG: KASAN: slab-out-of-bounds in nfsd+0x118/0xbc0 fs/nfsd/nfssvc.c:894 > Read of size 8 at addr ffff88802d423f50 by task nfsd/5988 >=20 > The list can be empty because nothing guarantees that a permanent > listener exists while a thread starts. With dynamic thread spawning, a > thread can begin running after the last listener has been closed and > removed. >=20 > Take sv_lock, which protects sv_permsocks, and check for an empty list > and read xpt_net in the same critical section. If there is no > permanent socket, report -ENOTCONN through svc_thread_init_status(), > which wakes the creator and exits the thread, instead of dereferencing > a bogus pointer. >=20 > Fixes: 88c476661719 ("nfsd: pass proper net to nfsd_destroy() from NFSd k= threads") > Reported-by: syzbot+561b859d032c8bf2fb53@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=3D561b859d032c8bf2fb53 > Tested-by: syzbot+561b859d032c8bf2fb53@syzkaller.appspotmail.com > Signed-off-by: Deepanshu Kartikey > --- > fs/nfsd/nfssvc.c | 22 ++++++++++++++++++---- > 1 file changed, 18 insertions(+), 4 deletions(-) >=20 > diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c > index 2edf716ea022..da6fce79efae 100644 > --- a/fs/nfsd/nfssvc.c > +++ b/fs/nfsd/nfssvc.c > @@ -890,17 +890,31 @@ nfsd(void *vrqstp) > { > struct svc_rqst *rqstp =3D (struct svc_rqst *) vrqstp; > struct svc_pool *pool =3D rqstp->rq_pool; > - struct svc_xprt *perm_sock =3D list_entry(rqstp->rq_server->sv_permsock= s.next, typeof(struct svc_xprt), xpt_list); > - struct net *net =3D perm_sock->xpt_net; > - struct nfsd_net *nn =3D net_generic(net, nfsd_net_id); > + struct svc_serv *serv =3D rqstp->rq_server; > + struct svc_xprt *perm_sock; > + struct net *net =3D NULL; > + struct nfsd_net *nn =3D NULL; > struct nfsd_thread_local_info ntli =3D { }; > bool have_mutex =3D false; > + int err =3D 0; > + > + spin_lock_bh(&serv->sv_lock); > + if (list_empty(&serv->sv_permsocks)) { > + err =3D -ENOTCONN; > + } else { > + perm_sock =3D list_first_entry(&serv->sv_permsocks, > + struct svc_xprt, xpt_list); > + net =3D perm_sock->xpt_net; > + } > + spin_unlock_bh(&serv->sv_lock); >=20 >=20 There is another way to get to the nfsd_net here. It turns out that the sv_stats field for nfsd always points to the one embedded in nfsd_net, so we could avoid the socket lists altogether by just doing something like: struct nfsd_net *nn =3D container_of(rqstp->rq_server->sv_stats, struct nfsd_net, nfsd_svcstats); That avoids the extra locking, but it seems a little weird to depend on the sv_stats field. Maybe we could wrap that in a little helper or something to make it less ugly? An alternative would be to add a serv->sv_net field, but most services are not per-net. nfsd is the exception so it's the only one that would use it. > =20 > + if (!err) > + nn =3D net_generic(net, nfsd_net_id); > /* At this point, the thread shares current->fs > * with the init process. We need to create files with the > * umask as defined by the client instead of init's umask. > */ > - svc_thread_init_status(rqstp, unshare_fs_struct()); > + svc_thread_init_status(rqstp, err ?: unshare_fs_struct()); > =20 > current->fs->umask =3D 0; > =20 --=20 Jeff Layton