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ptrace_stop: fix racy nonstop_code setting 

If the tracer is gone and we are not going to stop, ptrace_stop() sets
->exit_code = nostop_code.  However, the tracer could actually clear the
exit code before detaching.  In that case get_signal_to_deliver() "resends"
the signal which was cancelled by the debugger.  For example, it is
possible that a quick PTRACE_ATTACH + PTRACE_DETACH can leave the tracee in
STOPPED state.

Change the behaviour of ptrace_stop().  If the caller is ptrace notify(),
we should always clear ->exit_code.  If the caller is
get_signal_to_deliver(), we should not touch it at all.  To do so, change
the nonstop_code parameter to "bool clear_code" and change the callers
accordingly.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2008-02-08 04:19:03 -08:00 committed by Linus Torvalds
parent 9cbab81005
commit 20686a309a
1 changed files with 7 additions and 6 deletions
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13
kernel/signal.c
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@ -1591,10 +1591,10 @@ static int sigkill_pending(struct task_struct *tsk)
* That makes it a way to test a stopped process for
* being ptrace-stopped vs being job-control-stopped.
*
* If we actually decide not to stop at all because the tracer is gone,
* we leave nostop_code in current->exit_code.
* If we actually decide not to stop at all because the tracer
* is gone, we keep current->exit_code unless clear_code.
*/
static void ptrace_stop(int exit_code, int nostop_code, siginfo_t *info)
static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info)
{
int killed = 0;
@ -1641,7 +1641,8 @@ static void ptrace_stop(int exit_code, int nostop_code, siginfo_t *info)
* Don't drop the lock yet, another tracer may come.
*/
__set_current_state(TASK_RUNNING);
current->exit_code = nostop_code;
if (clear_code)
current->exit_code = 0;
read_unlock(&tasklist_lock);
}
@ -1675,7 +1676,7 @@ void ptrace_notify(int exit_code)
/* Let the debugger run. */
spin_lock_irq(&current->sighand->siglock);
ptrace_stop(exit_code, 0, &info);
ptrace_stop(exit_code, 1, &info);
spin_unlock_irq(&current->sighand->siglock);
}
@ -1782,7 +1783,7 @@ relock:
ptrace_signal_deliver(regs, cookie);
/* Let the debugger run. */
ptrace_stop(signr, signr, info);
ptrace_stop(signr, 0, info);
/* We're back. Did the debugger cancel the sig? */
signr = current->exit_code;