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SubjectAUDIT: copy_from_user is a deathtrap.

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

/* 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)

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,
Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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