ptrace_stop: fix racy nonstop_code setting

[Linux Kernel Mailing List]

Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=20686a309aa98c518adbbd9b57cdbb1804143deb
Commit:     20686a309aa98c518adbbd9b57cdbb1804143deb
Parent:     9cbab8100538efdd93aeae6fc37787d986f2f558
Author:     Oleg Nesterov <[EMAIL PROTECTED]>
AuthorDate: Fri Feb 8 04:19:03 2008 -0800
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Fri Feb 8 09:22:26 2008 -0800

    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 <[EMAIL PROTECTED]>
    Acked-by: Roland McGrath <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 kernel/signal.c |   13 +++++++------
 1 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 678bffa..3fca710 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -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;
-
To unsubscribe from this list: send the line "unsubscribe git-commits-head" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at  http://vger.kernel.org/majordomo-info.html