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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id q3sm7411290pgf.18.2021.08.27.08.04.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Aug 2021 08:04:28 -0700 (PDT) From: Kees Cook To: Tejun Heo Cc: Kees Cook , Stephen Rothwell , Zefan Li , Johannes Weiner , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH v2] cgroup: Avoid compiler warnings with no subsystems Date: Fri, 27 Aug 2021 08:04:24 -0700 Message-Id: <20210827150424.2729274-1-keescook@chromium.org> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3945; h=from:subject; bh=GFK3BETQmfQB9ONseeh+QxRF9yf/a6MqKtjDJoZzqeA=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBhKP74SaubLPqskWOEDTayM2+b9dEi4jnuGNQvHGBR dbuO1zCJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCYSj++AAKCRCJcvTf3G3AJs/ZD/ 4nZI7nyxeKoS/vLqeVHPIvoLfK1l5E/MD6+mX9oxiTv2+rWvwB+LEqyQsAeWZhefkPXXtHMlSKlfZf wfngNKG3xBkDUzhHgrPH6rw0jXrzoxLQ+RziHvHD05OqAzdfEn9rqkpTRMDklEEuWtApzTu7d+e6Dk +MXPDo7l+RrVk3CHNyjvM5sz5dHE4Yx8J9WISnfgMxfKymmCsm9hW/ekMILXJhLObzsCBxtpLrhJA6 X7ghcNxXlrFlvwnteEiSYkz+8Lo5+rKXwL8DagDfwkxuCGzDQ0G86atUitohjKT70bvqKK3XlpUl+A R3/njlqqexcL9f1UoODTtGPU0rnYsj2GXoOH/iRX1wJD95tG9hOa/h7/FDkVUC8E7RhboN/0EyX57/ oswoRaZlkjUWKfHZQXYzFCl6vYIdPX8bCzqqvVXNMkwojxLHqCJ521sBuGKKMmfo86PbNOQAq6OcSW fWhNjsjZ/pgqnROVQGFyXA/Yu+9P7F34MJlrpzItf55SYOtML5fiObXzJPoG7AU6woH0md7QjAJW1i lfXc9OGmU3RqAyGV6XEo7tjbUGZ4uxhAqtQVnBdTva2n88emli1eqk6j111Hb1uEhqkLJhey4K96QQ 42Myh/Q9bRh4WDV+hP4sfQ0Aub1+R4QMdLj+6ppDmC0jhcsvC/gDYadUhqig== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org As done before in commit cb4a31675270 ("cgroup: use bitmask to filter for_each_subsys"), avoid compiler warnings for the pathological case of having no subsystems (i.e. CGROUP_SUBSYS_COUNT == 0). This condition is hit for the arm multi_v7_defconfig config under -Wzero-length-bounds: In file included from ./arch/arm/include/generated/asm/rwonce.h:1, from include/linux/compiler.h:264, from include/uapi/linux/swab.h:6, from include/linux/swab.h:5, from arch/arm/include/asm/opcodes.h:86, from arch/arm/include/asm/bug.h:7, from include/linux/bug.h:5, from include/linux/thread_info.h:13, from include/asm-generic/current.h:5, from ./arch/arm/include/generated/asm/current.h:1, from include/linux/sched.h:12, from include/linux/cgroup.h:12, from kernel/cgroup/cgroup-internal.h:5, from kernel/cgroup/cgroup.c:31: kernel/cgroup/cgroup.c: In function 'of_css': kernel/cgroup/cgroup.c:651:42: warning: array subscript '' is outside the bounds of an interior zero-length array 'struct cgroup_subsys_state *[0]' [-Wzero-length-bounds] 651 | return rcu_dereference_raw(cgrp->subsys[cft->ss->id]); Reported-by: Stephen Rothwell Cc: Tejun Heo Cc: Zefan Li Cc: Johannes Weiner Cc: cgroups@vger.kernel.org Signed-off-by: Kees Cook --- v2: avoid "converting the enum constant to a boolean" warnings https://lore.kernel.org/lkml/202108271524.oOIHtG9S-lkp@intel.com/ v1: https://lore.kernel.org/lkml/20210827034741.2214318-1-keescook@chromium.org/ --- kernel/cgroup/cgroup.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index d0725c1a8db5..76693a86e8b7 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -472,7 +472,7 @@ 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 (CGROUP_SUBSYS_COUNT > 0 && ss) return rcu_dereference_check(cgrp->subsys[ss->id], lockdep_is_held(&cgroup_mutex)); else @@ -550,6 +550,9 @@ struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp, { struct cgroup_subsys_state *css; + if (!CGROUP_SUBSYS_COUNT) + return NULL; + do { css = cgroup_css(cgrp, ss); @@ -577,6 +580,9 @@ struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp, { struct cgroup_subsys_state *css; + if (!CGROUP_SUBSYS_COUNT) + return NULL; + rcu_read_lock(); do { @@ -647,7 +653,7 @@ 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 (CGROUP_SUBSYS_COUNT > 0 && cft->ss) return rcu_dereference_raw(cgrp->subsys[cft->ss->id]); else return &cgrp->self; @@ -2372,7 +2378,7 @@ struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset, struct css_set *cset = tset->cur_cset; struct task_struct *task = tset->cur_task; - while (&cset->mg_node != tset->csets) { + while (CGROUP_SUBSYS_COUNT > 0 && &cset->mg_node != tset->csets) { if (!task) task = list_first_entry(&cset->mg_tasks, struct task_struct, cg_list); @@ -4643,7 +4649,7 @@ void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags, it->ss = css->ss; it->flags = flags; - if (it->ss) + if (CGROUP_SUBSYS_COUNT > 0 && it->ss) it->cset_pos = &css->cgroup->e_csets[css->ss->id]; else it->cset_pos = &css->cgroup->cset_links; -- 2.30.2