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Wed, 06 Aug 2025 17:33:58 -0700 (PDT) Received: from jpkobryn-fedora-PF5CFKNC.thefacebook.com ([2620:10d:c090:500::4:b5a3]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-76bccfd8ebbsm16635973b3a.102.2025.08.06.17.33.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 Aug 2025 17:33:58 -0700 (PDT) From: JP Kobryn To: tj@kernel.org, shakeel.butt@linux.dev, mkoutny@suse.com, yosryahmed@google.com, hannes@cmpxchg.org, akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, kernel-team@meta.com Subject: [PATCH cgroup/for-6.16-fixes] cgroup: avoid null de-ref in css_rstat_exit() Date: Wed, 6 Aug 2025 17:33:50 -0700 Message-ID: <20250807003350.178160-1-inwardvessel@gmail.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit css_rstat_exit() may be called asynchronously in scenarios where preceding calls to css_rstat_init() have not completed. One such example is this sequence below: css_create(...) { ... init_and_link_css(css, ...); err = percpu_ref_init(...); if (err) goto err_free_css; err = cgroup_idr_alloc(...); if (err) goto err_free_css; err = css_rstat_init(css, ...); if (err) goto err_free_css; ... err_free_css: INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn); queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork); return ERR_PTR(err); } If any of the three goto jumps are taken, async cleanup will begin and css_rstat_exit() will be invoked on an uninitialized css->rstat_cpu. Avoid accessing the unitialized field by returning early in css_rstat_exit() if this is the case. Signed-off-by: JP Kobryn Suggested-by: Michal Koutný Fixes: 5da3bfa029d68 ("cgroup: use separate rstat trees for each subsystem") Reported-by: syzbot+8d052e8b99e40bc625ed@syzkaller.appspotmail.com Acked-by: Shakeel Butt --- kernel/cgroup/rstat.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index cbeaa499a96a..408e52d5f7a4 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -488,6 +488,9 @@ void css_rstat_exit(struct cgroup_subsys_state *css) if (!css_uses_rstat(css)) return; + if (!css->rstat_cpu) + return; + css_rstat_flush(css); /* sanity check */ -- 2.47.3