Hi all, I have a doubt about using pointers inside structs that are passed (as pointers) to ioctl argument. Since pointers passed from userspace can't be trusted, I need to copy they to kernel before accessing they. In this case I have a pointer inside a struct that is passed to the ioctl call also as pointer. So I need to copy the whole struct to kernel space and only then dereference the pointer. If this is true, two copy_from_user is needed right? Suppose I have a struct like this struct myioctl_arg { char *tx_buf; int tx_siz; } and this ioctl definition #define MYIOCTL_TX _IOWR(MY_MAGIC, MY_BASE, struct myioctl_arg *); At userspace program I do something like this: struct myioctl_arg arg = { .tx_buf = somebuf, .tx_siz = 32 } ioctl(fd, MYIOCTL_TX, &arg); And in my ioclt implementation static ioctl(struct file *fp, unsigned int cmd, unsigned long arg) { struct myioctl_arg karg; char kbuf[100]; ... case MYIOCTL_TX: copy_from_user(&karg, arg, sizeof(karg)); copy_from_user(kbuf, karg.tx_buf, karg.tx_siz); // now kbuf has the same contents of somebuf in userspace ... } I'm in doubt if this is the right way to access the userspace tx_buf. Since the .tx_buf from arg is a userspace pointer, accessible from userspace pointer arg, I can't type arg->tx_buf directly, doing this is dereferencing a userspace pointer inside kernel. So I need to copy the whole struct and dereference from the kernel space copy of it. So this two calls of copy_from_user() is the right way to do it? They are needed at all or is there better way of doing it? Cheers, -- "Do or do not. There is no try" Yoda Master