compat: Make compat_alloc_user_space() incorporate the access_ok()

compat_alloc_user_space() expects the caller to independently call
access_ok() to verify the returned area.  A missing call could
introduce problems on some architectures.

This patch incorporates the access_ok() check into
compat_alloc_user_space() and also adds a sanity check on the length.
The existing compat_alloc_user_space() implementations are renamed
arch_compat_alloc_user_space() and are used as part of the
implementation of the new global function.

This patch assumes NULL will cause __get_user()/__put_user() to either
fail or access userspace on all architectures.  This should be
followed by checking the return value of compat_access_user_space()
for NULL in the callers, at which time the access_ok() in the callers
can also be removed.

Reported-by: Ben Hawkes <[email protected]>
Signed-off-by: H. Peter Anvin <[email protected]>
Acked-by: Benjamin Herrenschmidt <[email protected]>
Acked-by: Chris Metcalf <[email protected]>
Acked-by: David S. Miller <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Acked-by: Thomas Gleixner <[email protected]>
Acked-by: Tony Luck <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: James Bottomley <[email protected]>
Cc: Kyle McMartin <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: <[email protected]>

arch/powerpc/include/asm/compat.h

@@ -134,7 +134,7 @@ static inline compat_uptr_t ptr_to_compat(void __user *uptr)
 	return (u32)(unsigned long)uptr;
 }
 
-static inline void __user *compat_alloc_user_space(long len)
+static inline void __user *arch_compat_alloc_user_space(long len)
 {
 	struct pt_regs *regs = current->thread.regs;
 	unsigned long usp = regs->gpr[1];