2006-05-17 22:19:50

by Chris Wright

Subject: [PATCH 21/22] [PATCH] Fix ptrace_attach()/ptrace_traceme()/de_thread() race

-stable review patch. If anyone has any objections, please let us know.
------------------

This holds the task lock (and, for ptrace_attach, the tasklist_lock)
over the actual attach event, which closes a race between attacking to a
thread that is either doing a PTRACE_TRACEME or getting de-threaded.

Thanks to Oleg Nesterov for reminding me about this, and Chris Wright
for noticing a lost return value in my first version.

Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Chris Wright <[email protected]>
---

kernel/ptrace.c | 39 +++++++++++++++++++++------------------
1 file changed, 21 insertions(+), 18 deletions(-)

--- linux-2.6.16.16.orig/kernel/ptrace.c
+++ linux-2.6.16.16/kernel/ptrace.c
@@ -149,12 +149,16 @@ int ptrace_may_attach(struct task_struct
int ptrace_attach(struct task_struct *task)
{
int retval;
- task_lock(task);
+
retval = -EPERM;
if (task->pid <= 1)
- goto bad;
+ goto out;
if (task->tgid == current->tgid)
- goto bad;
+ goto out;
+
+ write_lock_irq(&tasklist_lock);
+ task_lock(task);
+
/* the same process cannot be attached many times */
if (task->ptrace & PT_PTRACED)
goto bad;
@@ -167,17 +171,15 @@ int ptrace_attach(struct task_struct *ta
? PT_ATTACHED : 0);
if (capable(CAP_SYS_PTRACE))
task->ptrace |= PT_PTRACE_CAP;
- task_unlock(task);

- write_lock_irq(&tasklist_lock);
__ptrace_link(task, current);
- write_unlock_irq(&tasklist_lock);

force_sig_specific(SIGSTOP, task);
- return 0;

bad:
+ write_unlock_irq(&tasklist_lock);
task_unlock(task);
+out:
return retval;
}

@@ -418,21 +420,22 @@ int ptrace_request(struct task_struct *c
*/
int ptrace_traceme(void)
{
- int ret;
+ int ret = -EPERM;

/*
* Are we already being traced?
*/
- if (current->ptrace & PT_PTRACED)
- return -EPERM;
- ret = security_ptrace(current->parent, current);
- if (ret)
- return -EPERM;
- /*
- * Set the ptrace bit in the process ptrace flags.
- */
- current->ptrace |= PT_PTRACED;
- return 0;
+ task_lock(current);
+ if (!(current->ptrace & PT_PTRACED)) {
+ ret = security_ptrace(current->parent, current);
+ /*
+ * Set the ptrace bit in the process ptrace flags.
+ */
+ if (!ret)
+ current->ptrace |= PT_PTRACED;
+ }
+ task_unlock(current);
+ return ret;
}

/**

--