[PATCH 11/11] signal: Remove SA_IMMUTABLE

[Eric W. Biederman]

Now that fatal signals experience short circuit delivery in
__send_signal_locked.  There is no longer a race between sigaction
changing the signal handler and the signal handler being forced to
SIG_DFL, for fatal forced signals.

So remove SA_IMMUTABLE whose job it was to stop that race.
---
 include/linux/signal_types.h           | 3 ---
 include/uapi/asm-generic/signal-defs.h | 1 -
 kernel/signal.c                        | 9 +--------
 3 files changed, 1 insertion(+), 12 deletions(-)

diff --git a/include/linux/signal_types.h b/include/linux/signal_types.h
index caf4f7a59ab9..1a3bb540f1c7 100644
--- a/include/linux/signal_types.h
+++ b/include/linux/signal_types.h
@@ -70,9 +70,6 @@ struct ksignal {
 	int sig;
 };
 
-/* Used to kill the race between sigaction and forced signals */
-#define SA_IMMUTABLE		0x00800000
-
 #ifndef __ARCH_UAPI_SA_FLAGS
 #ifdef SA_RESTORER
 #define __ARCH_UAPI_SA_FLAGS	SA_RESTORER
diff --git a/include/uapi/asm-generic/signal-defs.h b/include/uapi/asm-generic/signal-defs.h
index 7572f2f46ee8..fe929e7b77ca 100644
--- a/include/uapi/asm-generic/signal-defs.h
+++ b/include/uapi/asm-generic/signal-defs.h
@@ -45,7 +45,6 @@
 #define SA_UNSUPPORTED	0x00000400
 #define SA_EXPOSE_TAGBITS	0x00000800
 /* 0x00010000 used on mips */
-/* 0x00800000 used for internal SA_IMMUTABLE */
 /* 0x01000000 used on x86 */
 /* 0x02000000 used on x86 */
 /*
diff --git a/kernel/signal.c b/kernel/signal.c
index 0b602dfb0b78..d1decfef86c0 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1328,8 +1328,6 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t,
 	blocked = sigismember(&t->blocked, sig);
 	if (blocked || ignored || (handler != HANDLER_CURRENT)) {
 		action->sa.sa_handler = SIG_DFL;
-		if (handler == HANDLER_EXIT)
-			action->sa.sa_flags |= SA_IMMUTABLE;
 		if (blocked)
 			sigdelset(&t->blocked, sig);
 	}
@@ -2946,8 +2944,7 @@ bool get_signal(struct ksignal *ksig)
 		if (!signr)
 			break; /* will return 0 */
 
-		if (unlikely(current->ptrace) && (signr != SIGKILL) &&
-		    !(sighand->action[signr -1].sa.sa_flags & SA_IMMUTABLE)) {
+		if (unlikely(current->ptrace) && (signr != SIGKILL)) {
 			signr = ptrace_signal(signr, &ksig->info, type);
 			if (!signr)
 				continue;
@@ -4351,10 +4348,6 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
 	k = &p->sighand->action[sig-1];
 
 	spin_lock_irq(&p->sighand->siglock);
-	if (k->sa.sa_flags & SA_IMMUTABLE) {
-		spin_unlock_irq(&p->sighand->siglock);
-		return -EINVAL;
-	}
 	if (oact)
 		*oact = *k;
 
-- 
2.41.0