linux-kernel - [PATCH v3 4/7] linux/signal.h: Ignore SIGINFO by default in new tasks

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Date:   Thu, 30 Apr 2020 09:42:58 +0300
From:   Arseny Maslennikov <ar@...msu.ru>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Arseny Maslennikov <ar@...msu.ru>, Rob Landley <rob@...dley.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Pavel Machek <pavel@....cz>, linux-api@...r.kernel.org,
        "Vladimir D. Seleznev" <vseleznv@...linux.org>
Subject: [PATCH v3 4/7] linux/signal.h: Ignore SIGINFO by default in new tasks

This matches the behaviour of other Unix-like systems that have SIGINFO
and causes less harm to processes that do not install handlers for this
signal, making the keyboard status character non-fatal for them.

This is implemented with the assumption that SIGINFO is defined
to be equivalent to SIGPWR; still, there is no reason for PWR to
result in termination of the signal recipient anyway — it does not
indicate there is a fatal problem with the recipient's execution
context (like e.g. FPE/ILL do), and we have TERM/KILL for explicit
termination requests.

To put it another way:
The only scenario where system behaviour actually changes is when the
signal recipient has default disposition for SIGPWR. If a process
chose to interpret a SIGPWR as an incentive to cleanly terminate, it
would supply its own handler — and this commit does not affect processes
with non-default handlers.

Signed-off-by: Arseny Maslennikov <ar@...msu.ru>
---
 include/linux/signal.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/signal.h b/include/linux/signal.h
index 05bacd2ab..dc31da8fc 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -369,7 +369,7 @@ extern bool unhandled_signal(struct task_struct *tsk, int sig);
  *	|  SIGSYS/SIGUNUSED  |	coredump 	|
  *	|  SIGSTKFLT         |	terminate	|
  *	|  SIGWINCH          |	ignore   	|
- *	|  SIGPWR            |	terminate	|
+ *	|  SIGPWR            |	ignore   	|
  *	|  SIGRTMIN-SIGRTMAX |	terminate       |
  *	+--------------------+------------------+
  *	|  non-POSIX signal  |  default action  |
@@ -420,7 +420,8 @@ extern bool unhandled_signal(struct task_struct *tsk, int sig);

 #define SIG_KERNEL_IGNORE_MASK (\
         rt_sigmask(SIGCONT)   |  rt_sigmask(SIGCHLD)   | \
-	rt_sigmask(SIGWINCH)  |  rt_sigmask(SIGURG)    )
+	rt_sigmask(SIGWINCH)  |  rt_sigmask(SIGURG)    | \
+	rt_sigmask(SIGINFO)			       )

 #define SIG_SPECIFIC_SICODES_MASK (\
 	rt_sigmask(SIGILL)    |  rt_sigmask(SIGFPE)    | \
-- 
2.26.2