linux-kernel - [PATCH] /dev/mem: Bail out upon SIGKILL when reading memory.

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Message-Id: <1566338811-4464-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
Date:   Wed, 21 Aug 2019 07:06:51 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        syzbot <syzbot+8ab2d0f39fb79fe6ca40@...kaller.appspotmail.com>
Subject: [PATCH] /dev/mem: Bail out upon SIGKILL when reading memory.

syzbot found that a thread can stall for minutes inside read_mem()
after that thread was killed by SIGKILL [1]. Reading 2GB at one read()
is legal, but delaying termination of killed thread for minutes is bad.

  [ 1335.912419][T20577] read_mem: sz=4096 count=2134565632
  [ 1335.943194][T20577] read_mem: sz=4096 count=2134561536
  [ 1335.978280][T20577] read_mem: sz=4096 count=2134557440
  [ 1336.011147][T20577] read_mem: sz=4096 count=2134553344
  [ 1336.041897][T20577] read_mem: sz=4096 count=2134549248

[1] https://syzkaller.appspot.com/bug?id=a0e3436829698d5824231251fad9d8e998f94f5e

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+8ab2d0f39fb79fe6ca40@...kaller.appspotmail.com>
---
 drivers/char/mem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index b08dc50..0f7d4c4 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -135,7 +135,7 @@ static ssize_t read_mem(struct file *file, char __user *buf,
 	if (!bounce)
 		return -ENOMEM;
 
-	while (count > 0) {
+	while (count > 0 && !fatal_signal_pending(current)) {
 		unsigned long remaining;
 		int allowed, probe;
 
-- 
1.8.3.1