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Fix ptrace_attach()/ptrace_traceme()/de_thread() race 

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 <torvalds@osdl.org>
This commit is contained in:
Linus Torvalds 2006-05-07 10:49:33 -07:00
parent 5528e568a7
commit f5b40e363a
1 changed files with 21 additions and 18 deletions
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39
kernel/ptrace.c
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@ -148,12 +148,16 @@ int ptrace_may_attach(struct task_struct *task)
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;
@ -166,17 +170,15 @@ int ptrace_attach(struct task_struct *task)
? 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;
}
@ -417,21 +419,22 @@ int ptrace_request(struct task_struct *child, long request,
*/
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;
}
/**