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Date:   Mon,  3 Feb 2020 13:22:16 -0800
Message-Id: <20200203212216.7076-1-surenb@google.com>
Mime-Version: 1.0
Subject: [PATCH] psi: Fix OOB write when writing 0 bytes to psi files
From:   Suren Baghdasaryan <surenb@google.com>
To:     surenb@google.com
Cc:     mingo@redhat.com, peterz@infradead.org, hannes@cmpxchg.org,
        juri.lelli@redhat.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, linux-kernel@vger.kernel.org,
        kernel-team@android.com
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Issuing write() with count parameter set to 0 on any file under
/proc/pressure/ will cause an OOB write because of the access to
buf[buf_size-1] when NUL-termination is performed. Fix this by checking
for buf_size to be non-zero.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 kernel/sched/psi.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index db7b50bba3f1..38ccd49b9bf6 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1199,6 +1199,9 @@ static ssize_t psi_write(struct file *file, const char __user *user_buf,
 	if (static_branch_likely(&psi_disabled))
 		return -EOPNOTSUPP;
 
+	if (!nbytes)
+		return -EINVAL;
+
 	buf_size = min(nbytes, sizeof(buf));
 	if (copy_from_user(buf, user_buf, buf_size))
 		return -EFAULT;
-- 
2.25.0.341.g760bfbb309-goog