linux-kernel - [PATCH 4.4 12/56] staging: comedi: jr3_pci: fix possible null pointer dereference

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Message-Id: <20170518104840.897591841@linuxfoundation.org>
Date:   Thu, 18 May 2017 12:48:29 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ian Abbott <abbotti@....co.uk>
Subject: [PATCH 4.4 12/56] staging: comedi: jr3_pci: fix possible null pointer dereference

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ian Abbott <abbotti@....co.uk>

commit 45292be0b3db0b7f8286683b376e2d9f949d11f9 upstream.

For some reason, the driver does not consider allocation of the
subdevice private data to be a fatal error when attaching the COMEDI
device.  It tests the subdevice private data pointer for validity at
certain points, but omits some crucial tests.  In particular,
`jr3_pci_auto_attach()` calls `jr3_pci_alloc_spriv()` to allocate and
initialize the subdevice private data, but the same function
subsequently dereferences the pointer to access the `next_time_min` and
`next_time_max` members without checking it first.  The other missing
test is in the timer expiry routine `jr3_pci_poll_dev()`, but it will
crash before it gets that far.

Fix the bug by returning `-ENOMEM` from `jr3_pci_auto_attach()` as soon
as one of the calls to `jr3_pci_alloc_spriv()` returns `NULL`.  The
COMEDI core will subsequently call `jr3_pci_detach()` to clean up.

Signed-off-by: Ian Abbott <abbotti@....co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/staging/comedi/drivers/jr3_pci.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/drivers/staging/comedi/drivers/jr3_pci.c
+++ b/drivers/staging/comedi/drivers/jr3_pci.c
@@ -726,11 +726,12 @@ static int jr3_pci_auto_attach(struct co
 		s->insn_read	= jr3_pci_ai_insn_read;

 		spriv = jr3_pci_alloc_spriv(dev, s);
-		if (spriv) {
-			/* Channel specific range and maxdata */
-			s->range_table_list	= spriv->range_table_list;
-			s->maxdata_list		= spriv->maxdata_list;
-		}
+		if (!spriv)
+			return -ENOMEM;
+
+		/* Channel specific range and maxdata */
+		s->range_table_list	= spriv->range_table_list;
+		s->maxdata_list		= spriv->maxdata_list;
 	}

 	/*  Reset DSP card */