[PATCH net] net: phylink: correctly validate returned PCS in phylink_inband_caps

[Christian Marangi <ansuelsmth@gmail.com>]

In phylink_inband_caps(), the PCS returned by mac_select_pcs is only
checked if NULL but mac_select_pcs can also return an error pointer.

This can cause a kernel panic as phylink_pcs_inband_caps() only checks
if passed PCS is not NULL and directly dereference ops from the phylink_pcs
struct.

Use the IS_ERR_OR_NULL macro to address both case where the returned
PCS can be NULL or an error pointer and prevent a kernel panic.

Cc: stable@vger.kernel.org
Fixes: df874f9e52c3 ("net: phylink: add pcs_inband_caps() method")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
---
 drivers/net/phy/phylink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 5b8e956902fb..3ec3bb439109 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -964,7 +964,7 @@ static unsigned int phylink_inband_caps(struct phylink *pl,
 		return 0;
 
 	pcs = pl->mac_ops->mac_select_pcs(pl->config, interface);
-	if (!pcs)
+	if (IS_ERR_OR_NULL(pcs))
 		return 0;
 
 	return phylink_pcs_inband_caps(pcs, interface);
-- 
2.53.0