AUDIT: copy_from_user is a deathtrap.

From: Rusty Russell (rusty@rustcorp.com.au)
Date: Fri May 17 2002 - 04:27:54 EST

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.
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