yam: fix a missing-check bug

In yam_ioctl(), the concrete ioctl command is firstly copied from the
user-space buffer 'ifr->ifr_data' to 'ioctl_cmd' and checked through the
following switch statement. If the command is not as expected, an error
code EINVAL is returned. In the following execution the buffer
'ifr->ifr_data' is copied again in the cases of the switch statement to
specific data structures according to what kind of ioctl command is
requested. However, after the second copy, no re-check is enforced on the
newly-copied command. Given that the buffer 'ifr->ifr_data' is in the user
space, a malicious user can race to change the command between the two
copies. This way, the attacker can inject inconsistent data and cause
undefined behavior.

This patch adds a re-check in each case of the switch statement if there is
a second copy in that case, to re-check whether the command obtained in the
second copy is the same as the one in the first copy. If not, an error code
EINVAL will be returned.
Signed-off-by: Wenwen Wang <wang6495@umn.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hamradio/yam.c

@@ -966,6 +966,8 @@ static int yam_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 				 sizeof(struct yamdrv_ioctl_mcs));
 		if (IS_ERR(ym))
 			return PTR_ERR(ym);
+		if (ym->cmd != SIOCYAMSMCS)
+			return -EINVAL;
 		if (ym->bitrate > YAM_MAXBITRATE) {
 			kfree(ym);
 			return -EINVAL;
@@ -981,6 +983,8 @@ static int yam_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 		if (copy_from_user(&yi, ifr->ifr_data, sizeof(struct yamdrv_ioctl_cfg)))
 			 return -EFAULT;
 
+		if (yi.cmd != SIOCYAMSCFG)
+			return -EINVAL;
 		if ((yi.cfg.mask & YAM_IOBASE) && netif_running(dev))
 			return -EINVAL;		/* Cannot change this parameter when up */
 		if ((yi.cfg.mask & YAM_IRQ) && netif_running(dev))