linux-kernel - [patch] rapidio: dereferencing an error pointer

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Message-ID: <20160804052606.GF775@mwanda>
Date:	Thu, 4 Aug 2016 08:26:06 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Matt Porter <mporter@...nel.crashing.org>,
	Alexandre Bounine <alexandre.bounine@....com>
Cc:	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [patch] rapidio: dereferencing an error pointer

If riocm_ch_alloc() fails then we end up dereferencing the error
pointer.

The problem is that we're not unwinding in the reverse order from how
we allocate things so it gets confusing.  I've changed this around so
now "ch" is NULL when we are done with it after we call
riocm_put_channel().  That way we can check if it's NULL and avoid
calling riocm_put_channel() on it twice.

I renamed err_nodev to err_put_new_ch so that it better reflects what
the goto does.

Then because we had flipping things around, it means we don't neeed to
initialize the pointers to NULL and we can remove an if statement and
pull things in an indent level.

Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

diff --git a/drivers/rapidio/rio_cm.c b/drivers/rapidio/rio_cm.c
index cecc15a..3fa17ac 100644
--- a/drivers/rapidio/rio_cm.c
+++ b/drivers/rapidio/rio_cm.c
@@ -1080,8 +1080,8 @@ static int riocm_send_ack(struct rio_channel *ch)
 static struct rio_channel *riocm_ch_accept(u16 ch_id, u16 *new_ch_id,
 					   long timeout)
 {
-	struct rio_channel *ch = NULL;
-	struct rio_channel *new_ch = NULL;
+	struct rio_channel *ch;
+	struct rio_channel *new_ch;
 	struct conn_req *req;
 	struct cm_peer *peer;
 	int found = 0;
@@ -1155,6 +1155,7 @@ static struct rio_channel *riocm_ch_accept(u16 ch_id, u16 *new_ch_id,
 
 	spin_unlock_bh(&ch->lock);
 	riocm_put_channel(ch);
+	ch = NULL;
 	kfree(req);
 
 	down_read(&rdev_sem);
@@ -1172,7 +1173,7 @@ static struct rio_channel *riocm_ch_accept(u16 ch_id, u16 *new_ch_id,
 	if (!found) {
 		/* If peer device object not found, simply ignore the request */
 		err = -ENODEV;
-		goto err_nodev;
+		goto err_put_new_ch;
 	}
 
 	new_ch->rdev = peer->rdev;
@@ -1184,15 +1185,16 @@ static struct rio_channel *riocm_ch_accept(u16 ch_id, u16 *new_ch_id,
 
 	*new_ch_id = new_ch->id;
 	return new_ch;
+
+err_put_new_ch:
+	spin_lock_bh(&idr_lock);
+	idr_remove(&ch_idr, new_ch->id);
+	spin_unlock_bh(&idr_lock);
+	riocm_put_channel(new_ch);
+
 err_put:
-	riocm_put_channel(ch);
-err_nodev:
-	if (new_ch) {
-		spin_lock_bh(&idr_lock);
-		idr_remove(&ch_idr, new_ch->id);
-		spin_unlock_bh(&idr_lock);
-		riocm_put_channel(new_ch);
-	}
+	if (ch)
+		riocm_put_channel(ch);
 	*new_ch_id = 0;
 	return ERR_PTR(err);
 }