[PATCH] clk: validate pointer in __clk_disable()

[fengguang.wu@intel.com (Fengguang Wu)]

clk_get() returns -ENOENT on error and some careless caller might
dereference it without error checking:

In mxc_rnga_remove():

        struct clk *clk = clk_get(&pdev->dev, "rng");

	// ...

        clk_disable(clk);

Since it's insane to audit the lots of existing and future clk users,
let's add a check in the callee to avoid kernel panic and warn about
any buggy user.
---
 drivers/clk/clk.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 687b00d..7bd795bf9 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -464,6 +464,9 @@ static void __clk_disable(struct clk *clk)
 	if (!clk)
 		return;
 
+	if (WARN_ON(IS_ERR(clk)))
+		return;
+
 	if (WARN_ON(clk->enable_count == 0))
 		return;
 
-- 
1.7.10