ethtool: Fix potential kernel buffer overflow in ETHTOOL_GRXCLSRLALL

On a 32-bit machine, info.rule_cnt >= 0x40000000 leads to integer
overflow and the buffer may be smaller than needed.  Since
ETHTOOL_GRXCLSRLALL is unprivileged, this can presumably be used for at
least denial of service.
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>
Cc: stable@kernel.org
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/ethtool.c

@@ -347,8 +347,9 @@ static noinline_for_stack int ethtool_get_rxnfc(struct net_device *dev,
 
 	if (info.cmd == ETHTOOL_GRXCLSRLALL) {
 		if (info.rule_cnt > 0) {
-			rule_buf = kmalloc(info.rule_cnt * sizeof(u32),
-					   GFP_USER);
+			if (info.rule_cnt <= KMALLOC_MAX_SIZE / sizeof(u32))
+				rule_buf = kmalloc(info.rule_cnt * sizeof(u32),
+						   GFP_USER);
 			if (!rule_buf)
 				return -ENOMEM;
 		}