From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6D78FC4338F for ; Tue, 10 Aug 2021 23:05:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4CD4A60462 for ; Tue, 10 Aug 2021 23:05:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235227AbhHJXGF (ORCPT ); Tue, 10 Aug 2021 19:06:05 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:52594 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235196AbhHJXGE (ORCPT ); Tue, 10 Aug 2021 19:06:04 -0400 Received: from pps.filterd (m0109331.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 17AN4qsW001311 for ; Tue, 10 Aug 2021 16:05:41 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : content-type : content-transfer-encoding : mime-version; s=facebook; bh=cRLN2SCUIpI92oa0bqAiVwsv2LhB6vz9N2CKM95wEL0=; b=d6J5+ycELWdtkINXAKxiqmN7UDDreq8AB5nM5anVt3yxOTgakO5gUeKCBuwrp5WI8gQZ Jxzj5+/43TQ2pGkQYEiuGmmiSNy7cfNf+IwTuuiJ2y6dXo0UjCaDFgRb3thWR9lPKejQ dob6fo2xm/E25JVfTl4u+rFCCADr3/5dGAg= Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com with ESMTP id 3abyfm1ag7-4 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Tue, 10 Aug 2021 16:05:41 -0700 Received: from intmgw002.25.frc3.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:82::e) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Tue, 10 Aug 2021 16:05:39 -0700 Received: by devbig003.ftw2.facebook.com (Postfix, from userid 128203) id 3CEE85DB0538; Tue, 10 Aug 2021 16:05:37 -0700 (PDT) From: Yonghong Song To: CC: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , , Subject: [PATCH bpf v4] bpf: add rcu read_lock in bpf_get_current_[ancestor_]cgroup_id() helpers Date: Tue, 10 Aug 2021 16:05:37 -0700 Message-ID: <20210810230537.2864668-1-yhs@fb.com> X-Mailer: git-send-email 2.30.2 X-FB-Internal: Safe Content-Type: text/plain X-FB-Source: Intern X-Proofpoint-ORIG-GUID: fphMA-Y3oAteh5qx9q6TVBatYF-P1acO X-Proofpoint-GUID: fphMA-Y3oAteh5qx9q6TVBatYF-P1acO Content-Transfer-Encoding: quoted-printable X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-08-10_08:2021-08-10,2021-08-10 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 phishscore=0 lowpriorityscore=0 clxscore=1015 adultscore=0 bulkscore=0 suspectscore=0 priorityscore=1501 malwarescore=0 impostorscore=0 spamscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108100152 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Currently, if bpf_get_current_cgroup_id() or bpf_get_current_ancestor_cgroup_id() helper is called with sleepable programs e.g., sleepable fentry/fmod_ret/fexit/lsm programs, a rcu warning may appear. For example, if I added the following hack to test_progs/test_lsm sleepable fentry program test_sys_setdomainname: --- a/tools/testing/selftests/bpf/progs/lsm.c +++ b/tools/testing/selftests/bpf/progs/lsm.c @@ -168,6 +168,10 @@ int BPF_PROG(test_sys_setdomainname, struct pt_regs = *regs) int buf =3D 0; long ret; + __u64 cg_id =3D bpf_get_current_cgroup_id(); + if (cg_id =3D=3D 1000) + copy_test++; + ret =3D bpf_copy_from_user(&buf, sizeof(buf), ptr); if (len =3D=3D -2 && ret =3D=3D 0 && buf =3D=3D 1234) copy_test++; I will hit the following rcu warning: include/linux/cgroup.h:481 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active =3D 2, debug_locks =3D 1 1 lock held by test_progs/260: #0: ffffffffa5173360 (rcu_read_lock_trace){....}-{0:0}, at: __bpf_pro= g_enter_sleepable+0x0/0xa0 stack backtrace: CPU: 1 PID: 260 Comm: test_progs Tainted: G O 5.14.0-rc2= + #176 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-= 0-g155821a1990b-prebuilt.qemu.org 04/01/2014 Call Trace: dump_stack_lvl+0x56/0x7b bpf_get_current_cgroup_id+0x9c/0xb1 bpf_prog_a29888d1c6706e09_test_sys_setdomainname+0x3e/0x89c bpf_trampoline_6442469132_0+0x2d/0x1000 __x64_sys_setdomainname+0x5/0x110 do_syscall_64+0x3a/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae I can get similar warning using bpf_get_current_ancestor_cgroup_id() helper. syzbot reported a similar issue in [1] for syscall program. Helper bpf_get_current_cgroup_id() or bpf_get_current_ancestor_cgroup_id() has the following callchain: task_dfl_cgroup task_css_set task_css_set_check and we have #define task_css_set_check(task, __c) \ rcu_dereference_check((task)->cgroups, \ lockdep_is_held(&cgroup_mutex) || \ lockdep_is_held(&css_set_lock) || \ ((task)->flags & PF_EXITING) || (__c)) Since cgroup_mutex/css_set_lock is not held and the task is not existing and rcu read_lock is not held, a warning will be issued. Note that bpf sleepable program is protected by rcu_read_lock_trace(). The above sleepable bpf programs are already protected by migrate_disable(). Adding rcu_read_lock() in these two helpers will silence the above warning. I marked the patch fixing 95b861a7935b ("bpf: Allow bpf_get_current_ancestor_cgroup_id for tracing") which added bpf_get_current_ancestor_cgroup_id() to tracing programs in 5.14. I think backporting 5.14 is probably good enough as sleepable progrems are not widely used. This patch should fix [1] as well since syscall program is a sleepable program protected with migrate_disable(). [1] https://lore.kernel.org/bpf/0000000000006d5cab05c7d9bb87@google.com/ Reported-by: syzbot+7ee5c2c09c284495371f@syzkaller.appspotmail.com Fixes: 95b861a7935b ("bpf: Allow bpf_get_current_ancestor_cgroup_id for tra= cing") Signed-off-by: Yonghong Song --- kernel/bpf/helpers.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) Changelog: v3 -> v4: - ensure rcu_read_lock() region enclosing all accesses to cgroup. v2 -> v3: - use rcu_read_lock() protection for bpf_get_current_[ancestor_]cgroup_id() helper. v1 -> v2: - disallow bpf_get_current_[ancestor_]cgroup_id() helper. diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 7a97b2f4747d..55f83ea09dae 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -353,9 +353,15 @@ const struct bpf_func_proto bpf_jiffies64_proto =3D { #ifdef CONFIG_CGROUPS BPF_CALL_0(bpf_get_current_cgroup_id) { - struct cgroup *cgrp =3D task_dfl_cgroup(current); + struct cgroup *cgrp; + u64 cgrp_id; =20 - return cgroup_id(cgrp); + rcu_read_lock(); + cgrp =3D task_dfl_cgroup(current); + cgrp_id =3D cgroup_id(cgrp); + rcu_read_unlock(); + + return cgrp_id; } =20 const struct bpf_func_proto bpf_get_current_cgroup_id_proto =3D { @@ -366,13 +372,17 @@ const struct bpf_func_proto bpf_get_current_cgroup_id= _proto =3D { =20 BPF_CALL_1(bpf_get_current_ancestor_cgroup_id, int, ancestor_level) { - struct cgroup *cgrp =3D task_dfl_cgroup(current); + struct cgroup *cgrp; struct cgroup *ancestor; + u64 cgrp_id; =20 + rcu_read_lock(); + cgrp =3D task_dfl_cgroup(current); ancestor =3D cgroup_ancestor(cgrp, ancestor_level); - if (!ancestor) - return 0; - return cgroup_id(ancestor); + cgrp_id =3D ancestor ? cgroup_id(ancestor) : 0; + rcu_read_unlock(); + + return cgrp_id; } =20 const struct bpf_func_proto bpf_get_current_ancestor_cgroup_id_proto =3D { --=20 2.30.2