[PATCH v3] PCI: endpoint: Fix NULL pointer dereference for ->get_features()

[Shradha Todi]

get_features ops of pci_epc_ops may return NULL, causing NULL pointer
dereference in pci_epf_test_bind function. Let us add a check for
pci_epc_feature pointer in pci_epf_test_bind before we access it to avoid
any such NULL pointer dereference and return -ENOTSUPP in case
pci_epc_feature is not found.

When the patch is not applied and EPC features is not implemented in the
platform driver, we see the following dump due to kernel NULL pointer
dereference.

[  105.135936] Call trace:
[  105.138363]  pci_epf_test_bind+0xf4/0x388
[  105.142354]  pci_epf_bind+0x3c/0x80
[  105.145817]  pci_epc_epf_link+0xa8/0xcc
[  105.149632]  configfs_symlink+0x1a4/0x48c
[  105.153616]  vfs_symlink+0x104/0x184
[  105.157169]  do_symlinkat+0x80/0xd4
[  105.160636]  __arm64_sys_symlinkat+0x1c/0x24
[  105.164885]  el0_svc_common.constprop.3+0xb8/0x170
[  105.169649]  el0_svc_handler+0x70/0x88
[  105.173377]  el0_svc+0x8/0x640
[  105.176411] Code: d2800581 b9403ab9 f9404ebb 8b394f60 (f9400400)
[  105.182478] ---[ end trace a438e3c5a24f9df0 ]---

Fixes: 2c04c5b8eef79 ("PCI: pci-epf-test: Use pci_epc_get_features() to get
EPC features")

Reviewed-by: Pankaj Dubey <pankaj.dubey@xxxxxxxxxxx>
Signed-off-by: Sriram Dash <sriram.dash@xxxxxxxxxxx>
Signed-off-by: Shradha Todi <shradha.t@xxxxxxxxxxx>
---
v2: https://lkml.org/lkml/2020/12/18/691
v3:
   Addressed Bjorn's comment to enhance commit message by adding fixes tag

 drivers/pci/endpoint/functions/pci-epf-test.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
index e4e51d8..1b30774 100644
--- a/drivers/pci/endpoint/functions/pci-epf-test.c
+++ b/drivers/pci/endpoint/functions/pci-epf-test.c
@@ -830,13 +830,16 @@ static int pci_epf_test_bind(struct pci_epf *epf)
 		return -EINVAL;
 
 	epc_features = pci_epc_get_features(epc, epf->func_no);
-	if (epc_features) {
-		linkup_notifier = epc_features->linkup_notifier;
-		core_init_notifier = epc_features->core_init_notifier;
-		test_reg_bar = pci_epc_get_first_free_bar(epc_features);
-		pci_epf_configure_bar(epf, epc_features);
+	if (!epc_features) {
+		dev_err(&epf->dev, "epc_features not implemented\n");
+		return -EOPNOTSUPP;
 	}
 
+	linkup_notifier = epc_features->linkup_notifier;
+	core_init_notifier = epc_features->core_init_notifier;
+	test_reg_bar = pci_epc_get_first_free_bar(epc_features);
+	pci_epf_configure_bar(epf, epc_features);
+
 	epf_test->test_reg_bar = test_reg_bar;
 	epf_test->epc_features = epc_features;
 
-- 
2.7.4