From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: [PATCH 06/11] cgroup: fix -Wzero-length-bounds warnings Date: Mon, 22 Mar 2021 17:02:44 +0100 Message-ID: <20210322160253.4032422-7-arnd@kernel.org> References: <20210322160253.4032422-1-arnd@kernel.org> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1616429077; bh=yAy/I3E6cDxsmlVnV0YJAH5ZEQIRtNmu4zak4TbdMtM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UB5shkw7Yd4R5EAaTaJbKCgGMQHdzM6i80uoGxhNLAKr58/Z+hb/X02iDZFbFM5q7 ohBr0mnuKE2zD2dZIPp5mGV/8upXxQjJIfPGJp9PdMs6uae5VNAC7zYBRMfKWnHX2T dVcWKQocYTTmbDcT2P/QpYMSgUNzpEBC5mOFpZCLPDNYvMuLPWfLzgAFpKC9vWx2UV WcW6Gm/cjDbzo+bVOJsKrlf8DWJ6XKsV5KO6yCyvx8yAazXnd03HJIpEKsAL1WBIyL rctKK7FEjfv0XP7F/8O3bxyOq6H75TM+jdZPPW1bjsoXOWVbf0YQRUVNLoyOj2UQzP uTGmECN+tjDoA== In-Reply-To: <20210322160253.4032422-1-arnd-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> List-ID: Content-Type: text/plain; charset="us-ascii" To: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Martin Sebor , Tejun Heo , Zefan Li , Johannes Weiner Cc: Arnd Bergmann , x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, Ning Sun , Jani Nikula , Kalle Valo , Simon Kelley , James Smart , "James E.J. Bottomley" , Anders Larsen , Serge Hallyn , Imre Deak , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, tboot-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, intel-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org, dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org, ath11k-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-wireless-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-scsi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-security-module-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Roman Gushchin , Christian Brauner From: Arnd Bergmann When cgroups are enabled, but every single subsystem is turned off, CGROUP_SUBSYS_COUNT is zero, and the cgrp->subsys[] array has no members. gcc-11 points out that this leads to an invalid access in any function that might access this array: kernel/cgroup/cgroup.c: In function 'cgroup_addrm_files': kernel/cgroup/cgroup.c:460:58: warning: array subscript '' is outside the bounds of an interior zero-length array 'struct cgroup_subsys_state *[0]' [-Wzero-length-bounds] kernel/cgroup/cgroup.c:460:24: note: in expansion of macro 'rcu_dereference_check' 460 | return rcu_dereference_check(cgrp->subsys[ss->id], | ^~~~~~~~~~~~~~~~~~~~~ In file included from include/linux/cgroup.h:28, from kernel/cgroup/cgroup-internal.h:5, from kernel/cgroup/cgroup.c:31: include/linux/cgroup-defs.h:422:43: note: while referencing 'subsys' 422 | struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT]; I'm not sure what is expected to happen for such a configuration, presumably these functions are never calls in that case. Adding a sanity check in each function we get the warning for manages to shut up the warnings and do nothing instead. Signed-off-by: Arnd Bergmann --- I'm grouping this together with the -Wstringop-overread warnings, since the underlying logic in gcc seems to be the same. --- kernel/cgroup/cgroup.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 9153b20e5cc6..3477f1dc7872 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -456,7 +456,7 @@ static u16 cgroup_ss_mask(struct cgroup *cgrp) static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp, struct cgroup_subsys *ss) { - if (ss) + if (ss && (CGROUP_SUBSYS_COUNT > 0)) return rcu_dereference_check(cgrp->subsys[ss->id], lockdep_is_held(&cgroup_mutex)); else @@ -534,6 +534,9 @@ struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp, { struct cgroup_subsys_state *css; + if (CGROUP_SUBSYS_COUNT == 0) + return NULL; + do { css = cgroup_css(cgrp, ss); @@ -561,6 +564,9 @@ struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp, { struct cgroup_subsys_state *css; + if (CGROUP_SUBSYS_COUNT == 0) + return NULL; + rcu_read_lock(); do { @@ -630,7 +636,7 @@ struct cgroup_subsys_state *of_css(struct kernfs_open_file *of) * the matching css from the cgroup's subsys table is guaranteed to * be and stay valid until the enclosing operation is complete. */ - if (cft->ss) + if (cft->ss && CGROUP_SUBSYS_COUNT > 0) return rcu_dereference_raw(cgrp->subsys[cft->ss->id]); else return &cgrp->self; @@ -2343,6 +2349,9 @@ struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset, struct css_set *cset = tset->cur_cset; struct task_struct *task = tset->cur_task; + if (CGROUP_SUBSYS_COUNT == 0) + return NULL; + while (&cset->mg_node != tset->csets) { if (!task) task = list_first_entry(&cset->mg_tasks, @@ -4523,7 +4532,7 @@ void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags, it->ss = css->ss; it->flags = flags; - if (it->ss) + if (it->ss && CGROUP_SUBSYS_COUNT > 0) it->cset_pos = &css->cgroup->e_csets[css->ss->id]; else it->cset_pos = &css->cgroup->cset_links; -- 2.29.2