From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Biggers Subject: Re: [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled Date: Tue, 11 Jan 2022 10:48:42 -0800 Message-ID: References: <20220111071212.1210124-1-surenb@google.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1641926924; bh=5nGYIYBRmlX498OYXLYdWFITJZwpiQZZoetGM7GB/fE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Wd7AZGPkge+6cI3FvoFCWSh82K8CVRceabYCdOCrTyvHKDLqB1Q9P2A2tba+RaQqw POmUe9J82+/tMLueySgCXzzGAUtvrIwMxivx8KFmQCpZCdW+ViqxSNO8ghVbq7x7rk 9TZytphLIPVL5ayUv9kDm1o7LAoLdoPFw0ylo2ly+e6nR4IbrYxD1fVXSpGKRP9fGu zZ1gsocbGXmFjqfEkfD41WGCEQQpmkzit5KYHDHmkGwTVOMZQDYhgSzMkrNaD9tO3m g7Jkiij8SxNEBbWhKOmilIUU77Y3ES6H7fr7WvENO8Ux5hD+k2qYywSEZbtzAiYrW9 DPI6pWEz2c00w== Content-Disposition: inline In-Reply-To: <20220111071212.1210124-1-surenb@google.com> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Suren Baghdasaryan Cc: hannes@cmpxchg.org, torvalds@linux-foundation.org, tj@kernel.org, lizefan.x@bytedance.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, stable@vger.kernel.org, kernel-team@android.com, syzbot+cdb5dd11c97cc532efad@syzkaller.appspotmail.com On Mon, Jan 10, 2022 at 11:12:12PM -0800, Suren Baghdasaryan wrote: > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c > index cafb8c114a21..93b51a2104f7 100644 > --- a/kernel/cgroup/cgroup.c > +++ b/kernel/cgroup/cgroup.c > @@ -3642,6 +3642,12 @@ static ssize_t cgroup_pressure_write(struct kernfs_open_file *of, char *buf, > cgroup_get(cgrp); > cgroup_kn_unlock(of->kn); > > + /* Allow only one trigger per file descriptor */ > + if (ctx->psi.trigger) { > + cgroup_put(cgrp); > + return -EBUSY; > + } > + > psi = cgroup_ino(cgrp) == 1 ? &psi_system : &cgrp->psi; > new = psi_trigger_create(psi, buf, nbytes, res); > if (IS_ERR(new)) { > @@ -3649,8 +3655,7 @@ static ssize_t cgroup_pressure_write(struct kernfs_open_file *of, char *buf, > return PTR_ERR(new); > } > > - psi_trigger_replace(&ctx->psi.trigger, new); > - > + ctx->psi.trigger = new; > cgroup_put(cgrp); The write here needs to use smp_store_release(), since it is paired with the concurrent READ_ONCE() in psi_trigger_poll(). > @@ -1305,14 +1287,24 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf, > > buf[buf_size - 1] = '\0'; > > - new = psi_trigger_create(&psi_system, buf, nbytes, res); > - if (IS_ERR(new)) > - return PTR_ERR(new); > - > seq = file->private_data; > + > /* Take seq->lock to protect seq->private from concurrent writes */ > mutex_lock(&seq->lock); > - psi_trigger_replace(&seq->private, new); > + > + /* Allow only one trigger per file descriptor */ > + if (seq->private) { > + mutex_unlock(&seq->lock); > + return -EBUSY; > + } > + > + new = psi_trigger_create(&psi_system, buf, nbytes, res); > + if (IS_ERR(new)) { > + mutex_unlock(&seq->lock); > + return PTR_ERR(new); > + } > + > + seq->private = new; Likewise here. - Eric