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Subject[03/90] mtd: mtd_blkdevs: dont increase open count on error path
3.0-stable review patch.  If anyone has any objections, please let me know.

------------------
From: Brian Norris <computersforpeace@gmail.com>

commit 342ff28f5a2e5aa3236617bd2bddf6c749677ef2 upstream.

Some error paths in mtd_blkdevs were fixed in the following commit:

commit 94735ec4044a6d318b83ad3c5794e931ed168d10
mtd: mtd_blkdevs: fix error path in blktrans_open

But on these error paths, the block device's `dev->open' count is
already incremented before we check for errors. This meant that, while
the error path was handled correctly on the first time through
blktrans_open(), the device is erroneously considered already open on
the second time through.

This problem can be seen, for instance, when a UBI volume is
simultaneously mounted as a UBIFS partition and read through its
corresponding gluebi mtdblockX device. This results in blktrans_open()
passing its error checks (with `dev->open > 0') without actually having
a handle on the device. Here's a summarized log of the actions and
results with nandsim:
# modprobe nandsim
# modprobe mtdblock
# modprobe gluebi
# modprobe ubifs
# ubiattach /dev/ubi_ctrl -m 0
...
# ubimkvol /dev/ubi0 -N test -s 16MiB
...
# mount -t ubifs ubi0:test /mnt
# ls /dev/mtdblock*
/dev/mtdblock0 /dev/mtdblock1
# cat /dev/mtdblock1 > /dev/null
cat: can't open '/dev/mtdblock4': Device or resource busy
# cat /dev/mtdblock1 > /dev/null
CPU 0 Unable to handle kernel paging request at virtual address
fffffff0, epc == 8031536c, ra == 8031f280
Oops[#1]:
...
Call Trace:
[<8031536c>] ubi_leb_read+0x14/0x164
[<8031f280>] gluebi_read+0xf0/0x148
[<802edba8>] mtdblock_readsect+0x64/0x198
[<802ecfe4>] mtd_blktrans_thread+0x330/0x3f4
[<8005be98>] kthread+0x88/0x90
[<8000bc04>] kernel_thread_helper+0x10/0x18
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/mtd/mtd_blkdevs.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -215,7 +215,7 @@ static int blktrans_open(struct block_de

mutex_lock(&dev->lock);

- if (dev->open++)
+ if (dev->open)
goto unlock;

kref_get(&dev->ref);
@@ -235,6 +235,7 @@ static int blktrans_open(struct block_de
goto error_release;

unlock:
+ dev->open++;
mutex_unlock(&dev->lock);
blktrans_dev_put(dev);
return ret;



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