From nobody Sat Jul 25 17:33:42 2026 Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com [115.124.30.132]) (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 70FAD3CF1FC; Wed, 15 Jul 2026 08:43:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.132 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784104998; cv=none; b=nzLEbn/5IMA6tRMcirawxn8h+TTqsCOZdEyqsFYl3ZdWx7zoDDR1GeyWeT70kqlXlSTyezw0IaW+hsabJ4IOqOclFS9eB7yB2gKuMoGxtYRlapquoedVDvVptyVAu2yMlY9ZyaKHB3nlP4+Jve8yVH4MPL1/vmlBQ31qRJOUxkE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784104998; c=relaxed/simple; bh=5q0Y5I8yIawo2ynnBMhalYpb2NrtyICRNplR5jao6JE=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=DJ6jRfX3rpsfHDPmtQ5kqxtbE94EeG3/XBIyPMmBx+A3riVAdUvO7SuPb8aPo5K6giBhZYG3YN3XGUzZvmhJHBwreNOIJpqE3tLhlcmdDzBPi0NUcj6ZBrNWmdQjBknjSDCh+15gRXKYrbULJUVCHOO1ja0D4qI2izshrM7HQFE= 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=gp+8PHzg; arc=none smtp.client-ip=115.124.30.132 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="gp+8PHzg" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1784104978; h=From:To:Subject:Date:Message-Id:MIME-Version; bh=IAnvCrJF1q7w7fmz3FaNGMcNd/i1AfT8lqKrGtMAUZ8=; b=gp+8PHzgqHbvgE9eTyTtdC+3k0o+VdtUuzl470Vcp75RQNNhPnjLd5yf8RMdWKSy/8S9RvTjqfWcX78mRHO1BpDB6m8SiLNUGkFljIWu8hKHaMXmNp2XAWH9nUEbYiKRJ4YoYeeLWKno3LeavteehrVHdXHzr4wpbtd/T9z1wo4= X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R151e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033032089153;MF=lulie@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0X78Xw0Q_1784104977; Received: from localhost(mailfrom:lulie@linux.alibaba.com fp:SMTPD_---0X78Xw0Q_1784104977 cluster:ay36) by smtp.aliyun-inc.com; Wed, 15 Jul 2026 16:42:57 +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 6.6.y 1/2] cgroup/psi: Set of->priv to NULL upon file release Date: Wed, 15 Jul 2026 16:42:55 +0800 Message-Id: <20260715084256.43412-2-lulie@linux.alibaba.com> X-Mailer: git-send-email 2.32.0.3.g01195cf9f In-Reply-To: <20260715084256.43412-1-lulie@linux.alibaba.com> References: <20260715084256.43412-1-lulie@linux.alibaba.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Chen Ridong commit 94a4acfec14615e971eb2c9e1fa6c992c85ff6c6 upstream. Setting of->priv to NULL when the file is released enables earlier bug detection. This allows potential bugs to manifest as NULL pointer dereferences rather than use-after-free errors[1], which are generally more difficult to diagnose. [1] https://lore.kernel.org/cgroups/38ef3ff9-b380-44f0-9315-8b3714b0948d@hu= aweicloud.com/T/#m8a3b3f88f0ff3da5925d342e90043394f8b2091b Signed-off-by: Chen Ridong Signed-off-by: Tejun Heo Signed-off-by: Philo Lu --- kernel/cgroup/cgroup.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index e787dc0eacd7d..4a7d334be50a5 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -4061,6 +4061,7 @@ static void cgroup_file_release(struct kernfs_open_fi= le *of) cft->release(of); put_cgroup_ns(ctx->ns); kfree(ctx); + of->priv =3D NULL; } =20 static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf, --=20 2.47.3 From nobody Sat Jul 25 17:33:42 2026 Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com [115.124.30.130]) (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 AB03C3CD8CA; Wed, 15 Jul 2026 08:43:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.130 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784104984; cv=none; b=g4baPZjXvRzVi+/wqadY9tmsjBiO4PdxlEMC8I9d3d9NjlWiamn9NTwLwOAiwLBFcTZb/OwMy4OuDpPvWHefwWmrdES+aD9PGe9kjsirEXrlLP21jQxzieokdfOA61P6PXY4yGNvNeDUcAG/zok7MkpqKNEk+vMCT4HfmVZmrJk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784104984; c=relaxed/simple; bh=ycs+mN9RabwlhwD5CE575co4HGaYQoH70pQ78XvuNvU=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=juudO7PLSg+y7jEqcFZNzyVaqSmEu5utHmDZo0tAgN93jJjh+CDrWFPRArviYZbaeIfFTBPNmqGR2p5vlsZrslH08GkgWp3p/zlCQg6biP1nhH09u09s9WEDnDJNSrNe5nhRsPb6w0VLP2Z9OPAArr/DhhxdQYesNfA5564KxCk= 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=aevm4GHx; arc=none smtp.client-ip=115.124.30.130 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="aevm4GHx" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1784104979; h=From:To:Subject:Date:Message-Id:MIME-Version; bh=scQDkHTu4k7SgaJHMPX3ke5fiUwIFc+s0rlVtiQuedo=; b=aevm4GHxl3Ep+JcG0Ow/YlW8jMeEtKGl7NkhNlVDuePlRWLXOoUmqhT3yHzgBknSO15Yh8inRhPbh3LPRIBpK2zKqydwAXGakvgsi884htB/CxGytl7fx1Zi3nUNMgPvIJD8uumrgHW1vA/Z9y8idZm1Gu340KAwjKZsvZSPeO8= X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R591e4;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_---0X78ezD3_1784104978; Received: from localhost(mailfrom:lulie@linux.alibaba.com fp:SMTPD_---0X78ezD3_1784104978 cluster:ay36) by smtp.aliyun-inc.com; Wed, 15 Jul 2026 16:42:58 +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 6.6.y 2/2] sched/psi: fix race between file release and pressure write Date: Wed, 15 Jul 2026 16:42:56 +0800 Message-Id: <20260715084256.43412-3-lulie@linux.alibaba.com> X-Mailer: git-send-email 2.32.0.3.g01195cf9f In-Reply-To: <20260715084256.43412-1-lulie@linux.alibaba.com> References: <20260715084256.43412-1-lulie@linux.alibaba.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 =3D=3D=3D=3D =3D=3D=3D=3D 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 =3D of->priv; kfree(ctx); of->priv =3D 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=3D0 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D 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, f= alse) kernfs_show(false) kernfs_drain_open_files() cgroup_file_release(of) kfree(ctx) of->priv =3D NULL cgroup_kn_unlock() ... acquires cgroup_mutex ctx =3D 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=3D33e571025d88efd1312c 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 4a7d334be50a5..8bcf9f61c6a04 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -3775,33 +3775,41 @@ 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 =3D of->priv; + struct cgroup_file_ctx *ctx; struct psi_trigger *new; struct cgroup *cgrp; struct psi_group *psi; + ssize_t ret =3D 0; =20 cgrp =3D cgroup_kn_lock_live(of->kn, false); if (!cgrp) return -ENODEV; =20 - cgroup_get(cgrp); - cgroup_kn_unlock(of->kn); + ctx =3D of->priv; + if (!ctx) { + ret =3D -ENODEV; + goto out_unlock; + } =20 /* Allow only one trigger per file descriptor */ if (ctx->psi.trigger) { - cgroup_put(cgrp); - return -EBUSY; + ret =3D -EBUSY; + goto out_unlock; } =20 psi =3D cgroup_psi(cgrp); new =3D psi_trigger_create(psi, buf, res, of->file, of); if (IS_ERR(new)) { - cgroup_put(cgrp); - return PTR_ERR(new); + ret =3D PTR_ERR(new); + goto out_unlock; } =20 smp_store_release(&ctx->psi.trigger, new); - cgroup_put(cgrp); + +out_unlock: + cgroup_kn_unlock(of->kn); + if (ret) + return ret; =20 return nbytes; } --=20 2.47.3