av7110: check for negative array offset

commit cb26a24e upstream.

info->num comes from the user.  It's type int.  If the user passes
in a negative value that would cause memory corruption.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/media/dvb/ttpci/av7110_ca.c

@@ -277,7 +277,7 @@ static int dvb_ca_ioctl(struct inode *inode, struct file *file,
 	{
 		ca_slot_info_t *info=(ca_slot_info_t *)parg;
 
-		if (info->num > 1)
+		if (info->num < 0 || info->num > 1)
 			return -EINVAL;
 		av7110->ci_slot[info->num].num = info->num;
 		av7110->ci_slot[info->num].type = FW_CI_LL_SUPPORT(av7110->arm_app) ?