Re: [PATCH v4 4/9] epoll: Add implementation for epoll_ctl_batch

On 03/09/2015 09:49 PM, Fam Zheng wrote:

+	if (!cmds || ncmds <= 0 || ncmds > EP_MAX_BATCH)
+		return -EINVAL;
+	cmd_size = sizeof(struct epoll_ctl_cmd) * ncmds;
+	/* TODO: optimize for small arguments like select/poll with a stack
+	 * allocated buffer */
+
+	kcmds = kmalloc(cmd_size, GFP_KERNEL);
+	if (!kcmds)
+		return -ENOMEM;

You probably want to define EP_MAX_BATCH as some sane value much less
than INT_MAX/(sizeof(struct epoll_ctl_cmd)). While this avoids the
integer overflow from before, any user can cause the kernel to kmalloc
up to INT_MAX bytes. Probably not a huge deal because it's freed at the
end of the syscall, but generally not a great idea.