[RFC PATCH 3/3a] ptrace: add _ptrace_may_access()

[Ingo Molnar <mingo@elte.hu>]

* Oleg Nesterov <oleg@redhat.com> wrote:

> +	task_lock(task);
>  	retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH);
> +	task_unlock(task);
>  	if (retval)
> -		goto bad;
> +		goto unlock_creds;

Hm, that's a bit ugly - why dont you reuse ptrace_may_access(), 
which does much of this already?

That way we could save a little bit of code size.

Something like the patch below allows the reuse of the locked 
version of __ptrace_may_access and pushes the int->bool conversion 
into an inline.

Note that this will also be a micro-optimization: the compiler will 
be able to eliminate the inlined negation in the call sites (most of 
which use the value directly) - and thus we save the negation.

( Untested - if you test it then it has my signoff. Patch also does 
  a small cleanup in _ptrace_may_access() )

Hm?

	Ingo

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 59e133d..2cc01ec 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -99,8 +99,13 @@ extern void exit_ptrace(struct task_struct *tracer);
 #define PTRACE_MODE_ATTACH 2
 /* Returns 0 on success, -errno on denial. */
 extern int __ptrace_may_access(struct task_struct *task, unsigned int mode);
-/* Returns true on success, false on denial. */
-extern bool ptrace_may_access(struct task_struct *task, unsigned int mode);
+/* Also takes the task lock: */
+extern int _ptrace_may_access(struct task_struct *task, unsigned int mode);
+/* True on success, false on denial: */
+static inline bool ptrace_may_access(struct task_struct *task, unsigned int mode)
+{
+	return !_ptrace_may_access(task, mode);
+}
 
 static inline int ptrace_reparented(struct task_struct *child)
 {
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index e950805..f7efcc9 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -155,13 +155,15 @@ int __ptrace_may_access(struct task_struct *task, unsigned int mode)
 	return security_ptrace_may_access(task, mode);
 }
 
-bool ptrace_may_access(struct task_struct *task, unsigned int mode)
+int _ptrace_may_access(struct task_struct *task, unsigned int mode)
 {
 	int err;
+
 	task_lock(task);
 	err = __ptrace_may_access(task, mode);
 	task_unlock(task);
-	return !err;
+
+	return err;
 }
 
 int ptrace_attach(struct task_struct *task)