linux-kernel - [PATCH] mtd: maps: pcmciamtd: fix possible sleep-in-atomic-context bugs in pcmciamtd_set

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Date:   Wed, 18 Dec 2019 21:41:46 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     miquel.raynal@...tlin.com, richard@....at, vigneshr@...com
Cc:     linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH] mtd: maps: pcmciamtd: fix possible sleep-in-atomic-context bugs in pcmciamtd_set_vpp()

The driver may sleep while holding a spinlock.
The function call path (from bottom to top) in Linux 4.19 is:

drivers/pcmcia/pcmcia_resource.c, 312:
	mutex_lock in pcmcia_fixup_vpp
drivers/mtd/maps/pcmciamtd.c, 309: 
	pcmcia_fixup_vpp in pcmciamtd_set_vpp
drivers/mtd/maps/pcmciamtd.c, 306: 
	_raw_spin_lock_irqsave in pcmciamtd_set_vpp

drivers/pcmcia/pcmcia_resource.c, 312:
	mutex_lock in pcmcia_fixup_vpp
drivers/mtd/maps/pcmciamtd.c, 312: 
	pcmcia_fixup_vpp in pcmciamtd_set_vpp
drivers/mtd/maps/pcmciamtd.c, 306: 
	_raw_spin_lock_irqsave in pcmciamtd_set_vp

mutex_lock() may sleep at runtime.

To fix these bugs, pcmcia_fixup_vpp() is called without holding the
spinlock.

These bugs are found by a static analysis tool STCheck written by
myself.

Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
---
 drivers/mtd/maps/pcmciamtd.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/maps/pcmciamtd.c b/drivers/mtd/maps/pcmciamtd.c
index 70bb403f69f7..d2cd1708aa49 100644
--- a/drivers/mtd/maps/pcmciamtd.c
+++ b/drivers/mtd/maps/pcmciamtd.c
@@ -301,17 +301,23 @@ static void pcmciamtd_set_vpp(struct map_info *map, int on)
 	struct pcmciamtd_dev *dev = (struct pcmciamtd_dev *)map->map_priv_1;
 	struct pcmcia_device *link = dev->p_dev;
 	unsigned long flags;
+	int fixup_flag = 0;
 
 	pr_debug("dev = %p on = %d vpp = %d\n\n", dev, on, dev->vpp);
 	spin_lock_irqsave(&pcmcia_vpp_lock, flags);
 	if (on) {
 		if (++pcmcia_vpp_refcnt == 1)   /* first nested 'on' */
-			pcmcia_fixup_vpp(link, dev->vpp);
+			fixup_flag = 1;
 	} else {
 		if (--pcmcia_vpp_refcnt == 0)   /* last nested 'off' */
-			pcmcia_fixup_vpp(link, 0);
+			fixup_flag = 2;
 	}
 	spin_unlock_irqrestore(&pcmcia_vpp_lock, flags);
+
+	if (fixup_flag == 1)
+		pcmcia_fixup_vpp(link, dev->vpp);
+	else if (fixup_flag == 2)
+		pcmcia_fixup_vpp(link, 0);
 }
 
 
-- 
2.17.1