From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) (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 00DBB3CF1ED; Wed, 15 Jul 2026 08:43:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.113 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784104988; cv=none; b=a9qm9S8DuyPNV/aGxKkGJWI/iHomOfELDuepZO9skMbvuQHucWZxfK54qiUAvBRDm1ROKYoeH0mFwf5Vq4i+xmGaIQqJzzu2pNEVh90PA/R3C0qVhMvjneh6WIGcjAv/3vpKDzt2ITac6z95MlAsV3Dy+ioWc1DiepGaBmLa69E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784104988; c=relaxed/simple; bh=iJsJg+g6MBMuNhHEu9ynWHGU2QhiYY38D15jltqPFnE=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=cfBrrgxc8NLuOkgl6cDox+xGk/wNkVt/DRBgWrPlSYcBBmWDD89jb1oMLF3F4IjP8knOWTic1jPEm8bi37YleFLcstHVjtzf+N9RHfzKOiHwioJXoXtE8ILQ9+nMaNhsFfEgMx4bbDIdLOIGUFnhZ8gap+fEssizMdL1zDdVy9s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=mPvs2Cob; arc=none smtp.client-ip=115.124.30.113 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="mPvs2Cob" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1784104976; h=From:To:Subject:Date:Message-Id:MIME-Version; bh=ByhTT/vLqSbHN8I0/bttb/gwjVyOVrikOemJXx4oZmY=; b=mPvs2Cob4DTCYAxsVpTa+DvGVYhgSLOTtb3BuWDQZ+lpnMT2YywlzNlrc5apoQwuBnAV/NhpSW6wuOfG9Ue7SniZedKeTZ6DFNHkH6uMKjJDuoESRC8ylo0AqscQ9P0UNzkWgvWvUGnRtcAcVIeyDswS4asiyPpCmY75iRcm7vI= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam011083073210;MF=lulie@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0X78XYwz_1784104975; Received: from localhost(mailfrom:lulie@linux.alibaba.com fp:SMTPD_---0X78XYwz_1784104975 cluster:ay36) by smtp.aliyun-inc.com; Wed, 15 Jul 2026 16:42:55 +0800 From: Philo Lu To: stable@vger.kernel.org Cc: tj@kernel.org, hannes@cmpxchg.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, eadavis@qq.com, surenb@google.com, akpm@linux-foundation.org, dust.li@linux.alibaba.com Subject: [PATCH 6.1.y 2/2] sched/psi: fix race between file release and pressure write Date: Wed, 15 Jul 2026 16:42:53 +0800 Message-Id: <20260715084253.43276-3-lulie@linux.alibaba.com> X-Mailer: git-send-email 2.32.0.3.g01195cf9f In-Reply-To: <20260715084253.43276-1-lulie@linux.alibaba.com> References: <20260715084253.43276-1-lulie@linux.alibaba.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Edward Adam Davis commit a5b98009f16d8a5fb4a8ff9a193f5735515c38fa upstream. A potential race condition exists between pressure write and cgroup file release regarding the priv member of struct kernfs_open_file, which triggers the uaf reported in [1]. Consider the following scenario involving execution on two separate CPUs: CPU0 CPU1 ==== ==== vfs_rmdir() kernfs_iop_rmdir() cgroup_rmdir() cgroup_kn_lock_live() cgroup_destroy_locked() cgroup_addrm_files() cgroup_rm_file() kernfs_remove_by_name() kernfs_remove_by_name_ns() vfs_write() __kernfs_remove() new_sync_write() kernfs_drain() kernfs_fop_write_iter() kernfs_drain_open_files() cgroup_file_write() kernfs_release_file() pressure_write() cgroup_file_release() ctx = of->priv; kfree(ctx); of->priv = NULL; cgroup_kn_unlock() cgroup_kn_lock_live() cgroup_get(cgrp) cgroup_kn_unlock() if (ctx->psi.trigger) // here, trigger uaf for ctx, that is of->priv The cgroup_rmdir() is protected by the cgroup_mutex, it also safeguards the memory deallocation of of->priv performed within cgroup_file_release(). However, the operations involving of->priv executed within pressure_write() are not entirely covered by the protection of cgroup_mutex. Consequently, if the code in pressure_write(), specifically the section handling the ctx variable executes after cgroup_file_release() has completed, a uaf vulnerability involving of->priv is triggered. Therefore, the issue can be resolved by extending the scope of the cgroup_mutex lock within pressure_write() to encompass all code paths involving of->priv, thereby properly synchronizing the race condition occurring between cgroup_file_release() and pressure_write(). And, if an live kn lock can be successfully acquired while executing the pressure write operation, it indicates that the cgroup deletion process has not yet reached its final stage; consequently, the priv pointer within open_file cannot be NULL. Therefore, the operation to retrieve the ctx value must be moved to a point *after* the live kn lock has been successfully acquired. In another situation, specifically after entering cgroup_kn_lock_live() but before acquiring cgroup_mutex, there exists a different class of race condition: CPU0: write memory.pressure CPU1: write cgroup.pressure=0 =========================== ============================= kernfs_fop_write_iter() kernfs_get_active_of(of) pressure_write() cgroup_kn_lock_live(memory.pressure) cgroup_tryget(cgrp) kernfs_break_active_protection(kn) ... blocks on cgroup_mutex cgroup_pressure_write() cgroup_kn_lock_live(cgroup.pressure) cgroup_file_show(memory.pressure, false) kernfs_show(false) kernfs_drain_open_files() cgroup_file_release(of) kfree(ctx) of->priv = NULL cgroup_kn_unlock() ... acquires cgroup_mutex ctx = of->priv; // may now be NULL if (ctx->psi.trigger) // NULL dereference Consequently, there is a possibility that of->priv is NULL, the pressure write needs to check for this. Now that the scope of the cgroup_mutex has been expanded, the original explicit cgroup_get/put operations are no longer necessary, this is because acquiring/releasing the live kn lock inherently executes a cgroup get/put operation. [1] BUG: KASAN: slab-use-after-free in pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011 Call Trace: pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011 cgroup_file_write+0x36f/0x790 kernel/cgroup/cgroup.c:4311 kernfs_fop_write_iter+0x3b0/0x540 fs/kernfs/file.c:352 Allocated by task 9352: cgroup_file_open+0x90/0x3a0 kernel/cgroup/cgroup.c:4256 kernfs_fop_open+0x9eb/0xcb0 fs/kernfs/file.c:724 do_dentry_open+0x83d/0x13e0 fs/open.c:949 Freed by task 9353: cgroup_file_release+0xd6/0x100 kernel/cgroup/cgroup.c:4283 kernfs_release_file fs/kernfs/file.c:764 [inline] kernfs_drain_open_files+0x392/0x720 fs/kernfs/file.c:834 kernfs_drain+0x470/0x600 fs/kernfs/dir.c:525 Fixes: 0e94682b73bf ("psi: introduce psi monitor") Reported-by: syzbot+33e571025d88efd1312c@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=33e571025d88efd1312c Tested-by: syzbot+33e571025d88efd1312c@syzkaller.appspotmail.com Signed-off-by: Edward Adam Davis Reviewed-by: Chen Ridong Signed-off-by: Tejun Heo Signed-off-by: Philo Lu --- kernel/cgroup/cgroup.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index fe6cb64e7c662..dbd9420c5223c 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -3786,33 +3786,41 @@ static int cgroup_cpu_pressure_show(struct seq_file *seq, void *v) static ssize_t pressure_write(struct kernfs_open_file *of, char *buf, size_t nbytes, enum psi_res res) { - struct cgroup_file_ctx *ctx = of->priv; + struct cgroup_file_ctx *ctx; struct psi_trigger *new; struct cgroup *cgrp; struct psi_group *psi; + ssize_t ret = 0; cgrp = cgroup_kn_lock_live(of->kn, false); if (!cgrp) return -ENODEV; - cgroup_get(cgrp); - cgroup_kn_unlock(of->kn); + ctx = of->priv; + if (!ctx) { + ret = -ENODEV; + goto out_unlock; + } /* Allow only one trigger per file descriptor */ if (ctx->psi.trigger) { - cgroup_put(cgrp); - return -EBUSY; + ret = -EBUSY; + goto out_unlock; } psi = cgroup_psi(cgrp); new = psi_trigger_create(psi, buf, res, of->file, of); if (IS_ERR(new)) { - cgroup_put(cgrp); - return PTR_ERR(new); + ret = PTR_ERR(new); + goto out_unlock; } smp_store_release(&ctx->psi.trigger, new); - cgroup_put(cgrp); + +out_unlock: + cgroup_kn_unlock(of->kn); + if (ret) + return ret; return nbytes; } -- 2.47.3