Restrict clearing TIF_SIGPENDING
authorRoland McGrath <roland@redhat.com>
Wed, 6 Jun 2007 10:59:00 +0000 (03:59 -0700)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>
Thu, 7 Jun 2007 15:52:15 +0000 (08:52 -0700)
This patch should get a few birds.  It prevents sigaction calls from
clearing TIF_SIGPENDING in other threads, which could leak -ERESTART*.
And It fixes ptrace_stop not to clear it, which done at the syscall exit
stop could leak -ERESTART*.  It probably removes the harm from signalfd,
at least assuming it never calls dequeue_signal on kernel threads that
might have used block_all_signals.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/signal.c

index acdfc0549c6fd88c254f8d07009edcc123804bfb..fe590e00db8df24823280b0bbf94a1daead4cfb5 100644 (file)
@@ -105,7 +105,11 @@ static int recalc_sigpending_tsk(struct task_struct *t)
                set_tsk_thread_flag(t, TIF_SIGPENDING);
                return 1;
        }
                set_tsk_thread_flag(t, TIF_SIGPENDING);
                return 1;
        }
-       clear_tsk_thread_flag(t, TIF_SIGPENDING);
+       /*
+        * We must never clear the flag in another thread, or in current
+        * when it's possible the current syscall is returning -ERESTART*.
+        * So we don't clear it here, and only callers who know they should do.
+        */
        return 0;
 }
 
        return 0;
 }
 
@@ -121,7 +125,9 @@ void recalc_sigpending_and_wake(struct task_struct *t)
 
 void recalc_sigpending(void)
 {
 
 void recalc_sigpending(void)
 {
-       recalc_sigpending_tsk(current);
+       if (!recalc_sigpending_tsk(current))
+               clear_thread_flag(TIF_SIGPENDING);
+
 }
 
 /* Given the mask, find the first available signal that should be serviced. */
 }
 
 /* Given the mask, find the first available signal that should be serviced. */
@@ -385,7 +391,8 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
                        }
                }
        }
                        }
                }
        }
-       recalc_sigpending_tsk(tsk);
+       if (likely(tsk == current))
+               recalc_sigpending();
        if (signr && unlikely(sig_kernel_stop(signr))) {
                /*
                 * Set a marker that we have dequeued a stop signal.  Our
        if (signr && unlikely(sig_kernel_stop(signr))) {
                /*
                 * Set a marker that we have dequeued a stop signal.  Our
@@ -1580,8 +1587,9 @@ static void ptrace_stop(int exit_code, int nostop_code, siginfo_t *info)
        /*
         * Queued signals ignored us while we were stopped for tracing.
         * So check for any that we should take before resuming user mode.
        /*
         * Queued signals ignored us while we were stopped for tracing.
         * So check for any that we should take before resuming user mode.
+        * This sets TIF_SIGPENDING, but never clears it.
         */
         */
-       recalc_sigpending();
+       recalc_sigpending_tsk(current);
 }
 
 void ptrace_notify(int exit_code)
 }
 
 void ptrace_notify(int exit_code)