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SubjectRe: [PATCH][COMPAT] compat_sys_fcntl{,64} 1/9 Generic part

> Now there used to be some code that did:
>
> if (get_user(a, &userstruct->firstmember) ||
> __get_user(b, &userstruct->secondmember))
> return -EFAULT;
>
> Assuming that the access_ok in get_user for sizeof(firstmember) covers
> secondmember too which doesn't do access_ok in __get_user. This only
> works assuming it should handle 64bit pointers when there is a memory
> hole at the end of the user process space, otherwise it could
> access kernel pages directly after TASK_SIZE. x86-64 has a big enough
> hole there, i assume sparc64 and ia64 have too, but i don't know
> about the other 64bit ports.

Yeah there are a bunch of those in the ioctl and syscall translation
code that annoys me. ppc64 is safe too, but its not something we should
rely on.

Anton
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