linux-kernel - [PATCH] tty/isicom: Fix a possible sleep-in-atomic bug in WaitTillCardIsFree

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Date:   Tue, 12 Dec 2017 21:24:56 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     gregkh@...uxfoundation.org, jslaby@...e.com, acme@...ectiva.com.br
Cc:     linux-kernel@...r.kernel.org, Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH] tty/isicom: Fix a possible sleep-in-atomic bug in WaitTillCardIsFree

The driver may sleep under a spinlock.
The function call paths are:
isicom_activate (acquire the spinlock)
  isicom_setup_board
    drop_dtr_rts
      WaitTillCardIsFree
        msleep --> may sleep

isicom_set_termios
  isicom_config_port
    drop_dtr
      WaitTillCardIsFree
        msleep --> may sleep

isicom_tiocmset
  drop_dtr
    WaitTillCardIsFree
      msleep --> may sleep

Though "in_atomic" is used to check atomic context,
but it is not recommended to use in driver code (see include/linux/preempt.h).

To fix it, only using mdelay instead.

This bug is found by my static analysis tool(DSAC) and checked by my code review.


Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
---
 drivers/tty/isicom.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/tty/isicom.c b/drivers/tty/isicom.c
index 015686f..bdd3027 100644
--- a/drivers/tty/isicom.c
+++ b/drivers/tty/isicom.c
@@ -219,13 +219,9 @@ struct	isi_port {
 static int WaitTillCardIsFree(unsigned long base)
 {
 	unsigned int count = 0;
-	unsigned int a = in_atomic(); /* do we run under spinlock? */
 
 	while (!(inw(base + 0xe) & 0x1) && count++ < 100)
-		if (a)
-			mdelay(1);
-		else
-			msleep(1);
+		mdelay(1);
 
 	return !(inw(base + 0xe) & 0x1);
 }
-- 
1.7.9.5