4.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ville Viinikka <redacted>

commit bfe5b1b1e013f7b1c0fd2ac3b3c8c380114b3fb9 upstream.

Set 'idata->buf' to NULL so that it never gets returned without
initialization. This fixes a bug where mmc_blk_ioctl_cmd() would
free both 'idata' and 'idata->buf' but 'idata->buf' was returned
uninitialized.

Fixes: 1ff8950c0433 ("mmc: block: change to use kmalloc when copy data from userspace")
Signed-off-by: Ville Viinikka <redacted>
Signed-off-by: Ulf Hansson <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/mmc/card/block.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c

@@ -352,8 +352,10 @@ static struct mmc_blk_ioc_data *mmc_blk_
 		goto idata_err;
 	}
 
-	if (!idata->buf_bytes)
+	if (!idata->buf_bytes) {
+		idata->buf = NULL;
 		return idata;
+	}
 
 	idata->buf = kmalloc(idata->buf_bytes, GFP_KERNEL);
 	if (!idata->buf) {