linux-kernel - [patch] relay: check array offset before using it

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Message-ID: <20161013084947.GC16198@mwanda>
Date:   Thu, 13 Oct 2016 11:50:24 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Akash Goel <akash.goel@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Richard Weinberger <richard@....at>,
        Zhouyi Zhou <yizhouzhou@....ac.cn>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [patch] relay: check array offset before using it

Smatch complains that we started using the array offset before we
checked that it was valid.

Fixes: 017c59c042d0 ('relay: Use per CPU constructs for the relay channel buffer pointers')
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

diff --git a/kernel/relay.c b/kernel/relay.c
index da79a10..8f18d31 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -809,11 +809,11 @@ void relay_subbufs_consumed(struct rchan *chan,
 {
 	struct rchan_buf *buf;
 
-	if (!chan)
+	if (!chan || cpu >= NR_CPUS)
 		return;
 
 	buf = *per_cpu_ptr(chan->buf, cpu);
-	if (cpu >= NR_CPUS || !buf || subbufs_consumed > chan->n_subbufs)
+	if (!buf || subbufs_consumed > chan->n_subbufs)
 		return;
 
 	if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)