AUDIT: copy_from_user is a deathtrap.

[Rusty Russell <rusty@rustcorp.com.au>]

Linus,

	Should I change copy_to/from_user to return -EFAULT, or
introduce a new copy_to/from_uspace which does and start moving
everything across?

There are 5,500 uses of copy_to/from_user in 2.5.15.  52 of them use
the return value in a way which would be broken by it returning
-EFAULT.  51 of those don't need to (mainly cut & paste between serial
drivers).

	/* Returns amount which wasn't copied before EFAULT.  Used by mount. */
	static inline unsigned long
	gradual_copy_from_user(void *to, const void *from, unsigned long n)
	{
		unsigned long i;

		for (i = 0; i < n; i++, to++, from++) {
			if (copy_from_user(from, to, 1) != 0)
				break;
		}

		return n - i;
	}

There are 415 uses of copy_to/from_user which are wrong, despite an
audit 12 months ago by the Stanford checker.

Tired of auditing the same bugs,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.