linux-kernel - [PATCH v2] carl9170: fix debugfs crashes

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Message-Id: <238afe4926e979a46013129f8b8db48154e46963.1474476231.git.chunkeey@gmail.com>
Date:   Wed, 21 Sep 2016 18:49:36 +0200
From:   Christian Lamparter <chunkeey@...glemail.com>
To:     gregkh@...uxfoundation.org, Kalle Valo <kvalo@...eaurora.org>
Cc:     Christian Lamparter <chunkeey@...il.com>,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        Nicolai Stange <nicstange@...il.com>,
        Ben Greear <greearb@...delatech.com>
Subject: [PATCH v2] carl9170: fix debugfs crashes

Ben Greear reported:
> I see lots of instability as soon as I load up the carl9710 NIC.
> My application is going to be poking at it's debugfs files...
>
> BUG: KASAN: slab-out-of-bounds in carl9170_debugfs_read+0xd5/0x2a0
> [carl9170] at addr 0xffff8801bc1208b0
> Read of size 8 by task btserver/5888
> =======================================================================
> BUG kmalloc-256 (Tainted: G        W      ): kasan: bad access detected
> -----------------------------------------------------------------------
>
> INFO: Allocated in seq_open+0x50/0x100 age=2690 cpu=2 pid=772
>...

This breakage was caused by the introduction of intermediate
fops in debugfs by commit 9fd4dcece43a
("debugfs: prevent access to possibly dead file_operations at file open")

Thankfully, the original/real fops are still available in d_fsdata.

Reported-by: Ben Greear <greearb@...delatech.com>
Signed-off-by: Christian Lamparter <chunkeey@...il.com>
Cc: stable <stable@...r.kernel.org> # 4.7+
---
 drivers/net/wireless/ath/carl9170/debug.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/ath/carl9170/debug.c b/drivers/net/wireless/ath/carl9170/debug.c
index 6808db4..ec3a64e 100644
--- a/drivers/net/wireless/ath/carl9170/debug.c
+++ b/drivers/net/wireless/ath/carl9170/debug.c
@@ -75,7 +75,8 @@ static ssize_t carl9170_debugfs_read(struct file *file, char __user *userbuf,
 
 	if (!ar)
 		return -ENODEV;
-	dfops = container_of(file->f_op, struct carl9170_debugfs_fops, fops);
+	dfops = container_of(debugfs_real_fops(file),
+			     struct carl9170_debugfs_fops, fops);
 
 	if (!dfops->read)
 		return -ENOSYS;
@@ -127,7 +128,8 @@ static ssize_t carl9170_debugfs_write(struct file *file,
 
 	if (!ar)
 		return -ENODEV;
-	dfops = container_of(file->f_op, struct carl9170_debugfs_fops, fops);
+	dfops = container_of(debugfs_real_fops(file),
+			     struct carl9170_debugfs_fops, fops);
 
 	if (!dfops->write)
 		return -ENOSYS;
-- 
2.9.3