Re: [PATCH] use ptrace_get_task_struct in various places

[Christoph Hellwig <hch@lst.de>]

On Mon, Nov 07, 2005 at 10:11:49PM -0800, Andrew Morton wrote:
> Christoph Hellwig <hch@lst.de> wrote:
> >
> > The ptrace_get_task_struct() helper that I added as part of the ptrace
> > consolidation is usefull in variety of places that currently opencode
> > it.  Switch them to the common helper.
> 
> If we're going to export ptrace_get_task_struct() to the world it would be
> nice to document it too - things like returning zero and a NULL *childp is
> a little obscure.

done, patch below.

> In arch/ia64/ia32/sys_ia32.c this patch will cause PTRACE_TRACEME requests
> to be handled by ptrace_request()

you mean ptrace_get_task_struct?

> rather than by sys_ptrace(), which is a
> not-obviously-correct change.

sys_ptrace has the same code for it, in fact just about every ptrace
implementation uses ptrace_get_task_struct to handle that code,
but ptrace_get_task_struct can't be used by ia64 because some oddness
in the !PTRACE_TRACEME codepath.

> Was the omission of arch/ia64/kernel/ptrace.c:sys_ptrace() deliberate?

yes.  it has some oddness about finding the 'right' task_struct of a
multi-threaded process.


Index: linux-2.6/kernel/ptrace.c
===================================================================
--- linux-2.6.orig/kernel/ptrace.c	2005-11-10 15:36:12.000000000 +0100
+++ linux-2.6/kernel/ptrace.c	2005-11-10 15:46:05.000000000 +0100
@@ -407,6 +407,23 @@
 	return ret;
 }
 
+/**
+ * ptrace_get_task_struct  --  grab a task struct reference for ptrace
+ * @long:	ptrace request type
+ * @pid:	process to work on
+ * @childp:	task struct returned
+ *
+ * This function is a helper for ptrace implementations.  It checks
+ * permissions and then grabs a task struct for use of the actual
+ * ptrace implementation.  As a special case also handles PTRACE_TRACEME
+ * completely (as it's trivial and doesn't need a task_struct reference.
+ *
+ * The calling convention is a little bit odd: negative return value
+ * means failure, positive one sucess.  But even when this function
+ * suceeds @childp can be NULL and the calling ptrace implementation
+ * should return sucessfully immediately afterwards.  This is to support
+ * the PTRACE_TRACEME special case.
+ */
 int ptrace_get_task_struct(long request, long pid, struct task_struct **childp)
 {
 	struct task_struct *child;