[PATCH] error path in setup_arg_pages() misses vm_unacct_memory()

Pavel Emelianov and Kirill Korotaev observe that fs and arch users of
security_vm_enough_memory tend to forget to vm_unacct_memory when a
failure occurs further down (typically in setup_arg_pages variants).

These are all users of insert_vm_struct, and that reservation will only
be unaccounted on exit if the vma is marked VM_ACCOUNT: which in some
cases it is (hidden inside VM_STACK_FLAGS) and in some cases it isn't.

So x86_64 32-bit and ppc64 vDSO ELFs have been leaking memory into
Committed_AS each time they're run.  But don't add VM_ACCOUNT to them,
it's inappropriate to reserve against the very unlikely case that gdb
be used to COW a vDSO page - we ought to do something about that in
do_wp_page, but there are yet other inconsistencies to be resolved.

The safe and economical way to fix this is to let insert_vm_struct do
the security_vm_enough_memory check when it finds VM_ACCOUNT is set.

And the MIPS irix_brk has been calling security_vm_enough_memory before
calling do_brk which repeats it, doubly accounting and so also leaking.
Remove that, and all the fs and arch calls to security_vm_enough_memory:
give it a less misleading name later on.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-Off-By: Kirill Korotaev <dev@sw.ru>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/mips/kernel/sysirix.c

@@ -581,18 +581,13 @@ asmlinkage int irix_brk(unsigned long brk)
 	}
 
 	/*
-	 * Check if we have enough memory..
+	 * Ok, looks good - let it rip.
 	 */
-	if (security_vm_enough_memory((newbrk-oldbrk) >> PAGE_SHIFT)) {
+	if (do_brk(oldbrk, newbrk-oldbrk) != oldbrk) {
 		ret = -ENOMEM;
 		goto out;
 	}
-
-	/*
-	 * Ok, looks good - let it rip.
-	 */
 	mm->brk = brk;
-	do_brk(oldbrk, newbrk-oldbrk);
 	ret = 0;
 
 out: