tracehook: get_signal_to_deliver

This defines the tracehook_get_signal() hook to allow tracing code to slip
in before normal signal dequeuing.  This lays the groundwork for new
tracing features that can inject synthetic signals outside the normal
queue or control the disposition of delivered signals.  The calling
convention lets tracehook_get_signal() decide both exactly what will
happen and what signal number to report in the handler/exit.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 27 insertions, 11 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 1a942ce32ba0..10b31ecdd9c8 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1754,17 +1754,33 @@ relock:
                     do_signal_stop(0))
                         goto relock;
 
-                signr = dequeue_signal(current, &current->blocked, info);
-                if (!signr)
-                        break; /* will return 0 */
+                /*
+                 * Tracing can induce an artifical signal and choose sigaction.
+                 * The return value in @signr determines the default action,
+                 * but @info->si_signo is the signal number we will report.
+                 */
+                signr = tracehook_get_signal(current, regs, info, return_ka);
+                if (unlikely(signr < 0))
+                        goto relock;
+                if (unlikely(signr != 0))
+                        ka = return_ka;
+                else {
+                        signr = dequeue_signal(current, &current->blocked,
+                                               info);
 
-                if (signr != SIGKILL) {
-                        signr = ptrace_signal(signr, info, regs, cookie);
                         if (!signr)
-                                continue;
+                                break; /* will return 0 */
+
+                        if (signr != SIGKILL) {
+                                signr = ptrace_signal(signr, info,
+                                                      regs, cookie);
+                                if (!signr)
+                                        continue;
+                        }
+
+                        ka = &sighand->action[signr-1];
                 }
 
-                ka = &sighand->action[signr-1];
                 if (ka->sa.sa_handler == SIG_IGN) /* Do nothing.  */
                         continue;
                 if (ka->sa.sa_handler != SIG_DFL) {
@@ -1812,7 +1828,7 @@ relock:
                                 spin_lock_irq(&sighand->siglock);
                         }
 
-                        if (likely(do_signal_stop(signr))) {
+                        if (likely(do_signal_stop(info->si_signo))) {
                                 /* It released the siglock.  */
                                 goto relock;
                         }
@@ -1833,7 +1849,7 @@ relock:
 
                 if (sig_kernel_coredump(signr)) {
                         if (print_fatal_signals)
-                                print_fatal_signal(regs, signr);
+                                print_fatal_signal(regs, info->si_signo);
                         /*
                          * If it was able to dump core, this kills all
                          * other threads in the group and synchronizes with
@@ -1842,13 +1858,13 @@ relock:
                          * first and our do_group_exit call below will use
                          * that value and ignore the one we pass it.
                          */
-                        do_coredump((long)signr, signr, regs);
+                        do_coredump(info->si_signo, info->si_signo, regs);
                 }
 
                 /*
                  * Death signals, no core dump.
                  */
-                do_group_exit(signr);
+                do_group_exit(info->si_signo);
                 /* NOTREACHED */
         }
         spin_unlock_irq(&sighand->siglock);