linux-kernel - [PATCH 4.14 225/343] signal/cifs: Fix cifs_put_tcp_session to call send_sig instead of force

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Date:   Fri, 24 Jan 2020 10:30:43 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Namjae Jeon <namjae.jeon@...sung.com>,
        Jeff Layton <jlayton@...marydata.com>,
        Steve French <smfrench@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 225/343] signal/cifs: Fix cifs_put_tcp_session to call send_sig instead of force_sig

From: Eric W. Biederman <ebiederm@...ssion.com>

[ Upstream commit 72abe3bcf0911d69b46c1e8bdb5612675e0ac42c ]

The locking in force_sig_info is not prepared to deal with a task that
exits or execs (as sighand may change).  The is not a locking problem
in force_sig as force_sig is only built to handle synchronous
exceptions.

Further the function force_sig_info changes the signal state if the
signal is ignored, or blocked or if SIGNAL_UNKILLABLE will prevent the
delivery of the signal.  The signal SIGKILL can not be ignored and can
not be blocked and SIGNAL_UNKILLABLE won't prevent it from being
delivered.

So using force_sig rather than send_sig for SIGKILL is confusing
and pointless.

Because it won't impact the sending of the signal and and because
using force_sig is wrong, replace force_sig with send_sig.

Cc: Namjae Jeon <namjae.jeon@...sung.com>
Cc: Jeff Layton <jlayton@...marydata.com>
Cc: Steve French <smfrench@...il.com>
Fixes: a5c3e1c725af ("Revert "cifs: No need to send SIGKILL to demux_thread during umount"")
Fixes: e7ddee9037e7 ("cifs: disable sharing session and tcon and add new TCP sharing code")
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/cifs/connect.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index f523a9ca9574f..51bbb1c0b71ae 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -2320,7 +2320,7 @@ cifs_put_tcp_session(struct TCP_Server_Info *server, int from_reconnect)

 	task = xchg(&server->tsk, NULL);
 	if (task)
-		force_sig(SIGKILL, task);
+		send_sig(SIGKILL, task, 1);
 }

 static struct TCP_Server_Info *
-- 
2.20.1