There is a race between PTRACE_ATTACH and the real parent calling wait.
For a moment, the task is put in PT_PTRACED but with its parent still
pointing to its real_parent. In this circumstance, if the real parent
calls wait without the WUNTRACED flag, he can see a stopped child status,
which wait should never return without WUNTRACED when the caller is not
using ptrace. Here it is not the caller that is using ptrace, but some
third party.
This patch avoids this race condition by adding the PT_ATTACHED flag to
distinguish a real parent from a ptrace_attach parent when PT_PTRACED is
set, and then having wait use this flag to confirm that things are in order
and not consider the child ptraced when its ->ptrace flags are set but its
parent links have not yet been switched. (ptrace_check_attach also uses it
similarly to rule out a possible race with a bogus ptrace call by the real
parent during ptrace_attach.)
While looking into this, I noticed that every arch's sys_execve has:
current->ptrace &= ~PT_DTRACE;
with no locking at all. So, if an exec happens in a race with
PTRACE_ATTACH, you could wind up with ->ptrace not having PT_PTRACED set
because this store clobbered it. That will cause later BUG hits because
the parent links indicate ptracedness but the flag is not set. The patch
corrects all the places I found to use task_lock around diddling ->ptrace
when it's possible to be racing with ptrace_attach. (The ptrace operation
code itself doesn't have this issue because it already excludes anyone else
being in ptrace_attach.)
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
(char __user * __user *) regs.edx,
®s);
if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
/* Make sure we don't return using sysenter.. */
set_thread_flag(TIF_IRET);
}
goto out;
error = do_execve(filename, uargv, uenvp, ®s);
- if (error == 0)
+ if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
+ }
putname(filename);
out:
return error;
error = do_execve(filename, (char **) regs->gr[25],
(char **)regs->gr[24], regs);
- if (error == 0)
+ if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
+ }
putname(filename);
out:
goto out;
error = do_execve(filename, (char **) regs->gr[25],
(char **) regs->gr[24], regs);
- if (error == 0)
+ if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
+ }
putname(filename);
out:
goto out;
error = compat_do_execve(filename, compat_ptr(regs->gr[25]),
compat_ptr(regs->gr[24]), regs);
- if (error == 0)
+ if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
+ }
putname(filename);
out:
preempt_enable();
error = do_execve(filename, (char __user *__user *) a1,
(char __user *__user *) a2, regs);
- if (error == 0)
+ if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
+ }
putname(filename);
out:
return error;
error = do_execve(filename, (char __user * __user *) a1,
(char __user * __user *) a2, regs);
- if (error == 0)
+ if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
+ }
putname(filename);
out:
error = compat_do_execve(filename, compat_ptr(a1), compat_ptr(a2), regs);
- if (error == 0)
+ if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
+ }
putname(filename);
out:
compat_ptr(regs.gprs[4]), ®s);
if (error == 0)
{
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
current->thread.fp_regs.fpc=0;
__asm__ __volatile__
("sr 0,0\n\t"
error = do_execve(filename, (char __user * __user *) regs.gprs[3],
(char __user * __user *) regs.gprs[4], ®s);
if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
current->thread.fp_regs.fpc = 0;
if (MACHINE_HAS_IEEE)
asm volatile("sfpc %0,%0" : : "d" (0));
(char __user * __user *)uargv,
(char __user * __user *)uenvp,
®s);
- if (error == 0)
+ if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
+ }
putname(filename);
out:
return error;
(char __user * __user *)uargv,
(char __user * __user *)uenvp,
pregs);
- if (error == 0)
+ if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
+ }
putname(filename);
out:
unlock_kernel();
(char __user * __user *)regs->u_regs[base + UREG_I2],
regs);
putname(filename);
- if (error == 0)
+ if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
+ }
out:
return error;
}
current_thread_info()->xfsr[0] = 0;
current_thread_info()->fpsaved[0] = 0;
regs->tstate &= ~TSTATE_PEF;
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
}
out:
return error;
current_thread_info()->xfsr[0] = 0;
current_thread_info()->fpsaved[0] = 0;
regs->tstate &= ~TSTATE_PEF;
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
}
out:
return error;
#endif
error = do_execve(file, argv, env, ¤t->thread.regs);
if (error == 0){
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
set_cmdline(current_cmd());
}
return(error);
if (IS_ERR(filename))
return error;
error = compat_do_execve(filename, argv, envp, regs);
- if (error == 0)
+ if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
+ }
putname(filename);
return error;
}
if (IS_ERR(filename))
return error;
error = do_execve(filename, argv, envp, ®s);
- if (error == 0)
+ if (error == 0) {
+ task_lock(current);
current->ptrace &= ~PT_DTRACE;
+ task_unlock(current);
+ }
putname(filename);
return error;
}
#define PT_TRACE_EXEC 0x00000080
#define PT_TRACE_VFORK_DONE 0x00000100
#define PT_TRACE_EXIT 0x00000200
+#define PT_ATTACHED 0x00000400 /* parent != real_parent */
#define PT_TRACE_MASK 0x000003f4
}
+static inline int my_ptrace_child(struct task_struct *p)
+{
+ if (!(p->ptrace & PT_PTRACED))
+ return 0;
+ if (!(p->ptrace & PT_ATTACHED))
+ return 1;
+ /*
+ * This child was PTRACE_ATTACH'd. We should be seeing it only if
+ * we are the attacher. If we are the real parent, this is a race
+ * inside ptrace_attach. It is waiting for the tasklist_lock,
+ * which we have to switch the parent links, but has already set
+ * the flags in p->ptrace.
+ */
+ return (p->parent != p->real_parent);
+}
+
static long do_wait(pid_t pid, int options, struct siginfo __user *infop,
int __user *stat_addr, struct rusage __user *ru)
{
switch (p->state) {
case TASK_TRACED:
- if (!(p->ptrace & PT_PTRACED))
+ if (!my_ptrace_child(p))
continue;
/*FALLTHROUGH*/
case TASK_STOPPED:
if (!(options & WUNTRACED) &&
- !(p->ptrace & PT_PTRACED))
+ !my_ptrace_child(p))
continue;
retval = wait_task_stopped(p, ret == 2,
(options & WNOWAIT),
*/
read_lock(&tasklist_lock);
if ((child->ptrace & PT_PTRACED) && child->parent == current &&
- child->signal != NULL) {
+ (!(child->ptrace & PT_ATTACHED) || child->real_parent != current)
+ && child->signal != NULL) {
ret = 0;
spin_lock_irq(&child->sighand->siglock);
if (child->state == TASK_STOPPED) {
goto bad;
/* Go */
- task->ptrace |= PT_PTRACED;
+ task->ptrace |= PT_PTRACED | PT_ATTACHED;
if (capable(CAP_SYS_PTRACE))
task->ptrace |= PT_PTRACE_CAP;
task_unlock(task);
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