linux-kernel - [PATCH AUTOSEL 5.11 42/44] signal: don't allow sending any signals to PF_IO

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Date:   Thu, 25 Mar 2021 07:24:57 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>, Stefan Metzmacher <metze@...ba.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.11 42/44] signal: don't allow sending any signals to PF_IO_WORKER threads

From: Jens Axboe <axboe@...nel.dk>

[ Upstream commit 5be28c8f85ce99ed2d329d2ad8bdd18ea19473a5 ]

They don't take signals individually, and even if they share signals with
the parent task, don't allow them to be delivered through the worker
thread. Linux does allow this kind of behavior for regular threads, but
it's really a compatability thing that we need not care about for the IO
threads.

Reported-by: Stefan Metzmacher <metze@...ba.org>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/signal.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/signal.c b/kernel/signal.c
index 5ad8566534e7..55526b941011 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -833,6 +833,9 @@ static int check_kill_permission(int sig, struct kernel_siginfo *info,
 
 	if (!valid_signal(sig))
 		return -EINVAL;
+	/* PF_IO_WORKER threads don't take any signals */
+	if (t->flags & PF_IO_WORKER)
+		return -ESRCH;
 
 	if (!si_fromuser(info))
 		return 0;
-- 
2.30.1