sys/linux: limit init_module size argument

Kernel tries to vmalloc whatever we pass as size and it's not accounted against memcg.
As the result it can lead to massive OOM kills of everything running on the machine.
Strictly saying, the same applies to finit_module with a sparse file too,
but there is no simple way to handle that.

sys/linux/init.go

@@ -165,6 +165,13 @@ func (arch *arch) sanitizeCall(c *prog.Call) {
 		if uint64(uint32(cmd.Val)) == arch.ARCH_SET_FS {
 			cmd.Val = arch.ARCH_SET_GS
 		}
+	case "init_module":
+		// Kernel tries to vmalloc whatever we pass as size and it's not accounted against memcg.
+		// As the result it can lead to massive OOM kills of everything running on the machine.
+		// Strictly saying, the same applies to finit_module with a sparse file too,
+		// but there is no simple way to handle that.
+		sz := c.Args[1].(*prog.ConstArg)
+		sz.Val %= 1 << 20
 	case "syz_init_net_socket":
 		// Don't let it mess with arbitrary sockets in init namespace.
 		family := c.Args[0].(*prog.ConstArg)