[PATCH for-4.9.y] IB/ocrdma: fix out of bounds access to local buffer

[Amit Pundir <amit.pundir@linaro.org>]

From: Michael Mera <dev@michaelmera.com>

commit 062d0f22a30c39840ea49b72cfcfc1aa4cc538fa upstream.

In write to debugfs file 'resource_stats' the local buffer 'tmp_str' is
written at index 'count-1' where 'count' is the size of the write, so
potentially 0.

This patch filters odd values for the write size/position to avoid this
type of problem.

Signed-off-by: Michael Mera <dev@michaelmera.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
---
Please cherry-pick it on 4.4.y as well.
Not applicable for 3.18.y

 drivers/infiniband/hw/ocrdma/ocrdma_stats.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/infiniband/hw/ocrdma/ocrdma_stats.c b/drivers/infiniband/hw/ocrdma/ocrdma_stats.c
index 265943069b35..84349d976162 100644
--- a/drivers/infiniband/hw/ocrdma/ocrdma_stats.c
+++ b/drivers/infiniband/hw/ocrdma/ocrdma_stats.c
@@ -645,7 +645,7 @@ static ssize_t ocrdma_dbgfs_ops_write(struct file *filp,
 	struct ocrdma_stats *pstats = filp->private_data;
 	struct ocrdma_dev *dev = pstats->dev;
 
-	if (count > 32)
+	if (*ppos != 0 || count == 0 || count > sizeof(tmp_str))
 		goto err;
 
 	if (copy_from_user(tmp_str, buffer, count))
-- 
2.7.4