linux-kernel - [PATCH v2] staging:gpib: Fix a dereference before null check issue

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Message-ID: <20241121152221.6415-1-pperego@suse.de>
Date: Thu, 21 Nov 2024 16:22:21 +0100
From: Paolo Perego <pperego@...e.de>
To: linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Cc: Dave Penkler <dpenkler@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Kees Bakker <kees@...erbout.nl>,
	Paolo Perego <pperego@...e.de>,
	Arnd Bergmann <arnd@...db.de>
Subject: [PATCH v2] staging:gpib: Fix a dereference before null check issue

This commit fixes a dereference before null check issue discovered by 
Coverity (CID 1601566).

The check at line 1450 suggests that a_priv can be NULL, however it has
been dereferenced before, in the interface_to_usbdev() call.

After a discussion, the NULL check is useless because private data is allocated
in attach routine and freed in detach routine, so in detach routine the pointer
has to be not NULL for sure.

Signed-off-by: Paolo Perego <pperego@...e.de>
Fixes: Removes a useless NULL check

---
v2: 
* After a discussion, we agreed the NULL check is useless because private data
  is freed in detach routine and allocated while attaching. For such a reason,
  the pointer has to be not NULL while detaching the device

 .../gpib/agilent_82357a/agilent_82357a.c      | 20 +++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/staging/gpib/agilent_82357a/agilent_82357a.c b/drivers/staging/gpib/agilent_82357a/agilent_82357a.c
index bf05fb4a736b..e940429dea19 100644
--- a/drivers/staging/gpib/agilent_82357a/agilent_82357a.c
+++ b/drivers/staging/gpib/agilent_82357a/agilent_82357a.c
@@ -1447,17 +1447,17 @@ static void agilent_82357a_detach(gpib_board_t *board)
 
 	a_priv = board->private_data;
 	usb_dev = interface_to_usbdev(a_priv->bus_interface);
-	if (a_priv) {
-		if (a_priv->bus_interface) {
-			agilent_82357a_go_idle(board);
-			usb_set_intfdata(a_priv->bus_interface, NULL);
-		}
-		mutex_lock(&a_priv->control_alloc_lock);
-		mutex_lock(&a_priv->bulk_alloc_lock);
-		mutex_lock(&a_priv->interrupt_alloc_lock);
-		agilent_82357a_cleanup_urbs(a_priv);
-		agilent_82357a_free_private(a_priv);
+
+	if (a_priv->bus_interface) {
+		agilent_82357a_go_idle(board);
+		usb_set_intfdata(a_priv->bus_interface, NULL);
 	}
+	
+	mutex_lock(&a_priv->control_alloc_lock);
+	mutex_lock(&a_priv->bulk_alloc_lock);
+	mutex_lock(&a_priv->interrupt_alloc_lock);
+	agilent_82357a_cleanup_urbs(a_priv);
+	agilent_82357a_free_private(a_priv);
 	dev_info(&usb_dev->dev, "%s: detached\n", __func__);
 	mutex_unlock(&agilent_82357a_hotplug_lock);
 }
-- 
2.47.0