[PATCH] comedi: integer overflow in do_insnlist_ioctl()

[Xi Wang <xi.wang@gmail.com>]

There is a potential integer overflow in do_insnlist_ioctl() if userspace passes in a large insnlist.n_insns.  The call to kmalloc() would allocate a small buffer, which would result in a memory corruption.

Reported-by: Haogang Chen <haogangchen@gmail.com>
Signed-off-by: Xi Wang <xi.wang@gmail.com>
---
 drivers/staging/comedi/comedi_fops.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 21d8c1c..66bb49d 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -650,6 +650,7 @@ static int parse_insn(struct comedi_device *dev, struct comedi_insn *insn,
  *		data (for reads)
  */
 /* arbitrary limits */
+#define MAX_INSNS   256
 #define MAX_SAMPLES 256
 static int do_insnlist_ioctl(struct comedi_device *dev,
 			     struct comedi_insnlist __user *arg, void *file)
@@ -663,6 +664,12 @@ static int do_insnlist_ioctl(struct comedi_device *dev,
 	if (copy_from_user(&insnlist, arg, sizeof(struct comedi_insnlist)))
 		return -EFAULT;
 
+	if (insnlist.n_insns > MAX_INSNS) {
+		DPRINTK("invalid number of instructions\n");
+		ret = -EINVAL;
+		goto error;
+	}
+
 	data = kmalloc(sizeof(unsigned int) * MAX_SAMPLES, GFP_KERNEL);
 	if (!data) {
 		DPRINTK("kmalloc failed\n");
-- 
1.7.5.4