[PATCH v2] PCI: Fix NULL dereference in SR-IOV VF creation error path

[Shay Drory <shayd@nvidia.com>]

Add proper cleanup when virtfn setup fails to prevent NULL pointer
dereference during device removal. The kernel oops[1] occurred due to
Incorrect error handling flow when pci_setup_device() fails.

Fix it by introducing pci_iov_scan_device() which handle virtfn
allocation and setup properly, instead of invoking
pci_stop_and_remove_bus_device() whenever pci_setup_device is failed.
This prevents accessing partially initialized virtfn devices during
removal.

[1]
BUG: kernel NULL pointer dereference, address: 00000000000000d0
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP
CPU: 22 UID: 0 PID: 1151 Comm: bash Not tainted 6.13.0+ #1
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
RIP: 0010:device_del+0x3d/0x3d0
Call Trace:
 <TASK>
 ? __die+0x20/0x60
 ? page_fault_oops+0x150/0x3e0
 ? exc_page_fault+0x74/0x130
 ? asm_exc_page_fault+0x22/0x30
 ? device_del+0x3d/0x3d0
 pci_remove_bus_device+0x7c/0x100
 pci_iov_add_virtfn+0xfa/0x200
 sriov_enable+0x208/0x420
 mlx5_core_sriov_configure+0x6a/0x160 [mlx5_core]
 sriov_numvfs_store+0xae/0x1a0
 kernfs_fop_write_iter+0x109/0x1a0
 vfs_write+0x2c0/0x3e0
 ksys_write+0x62/0xd0
 do_syscall_64+0x4c/0x100
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

Fixes: e3f30d563a38 ("PCI: Make pci_destroy_dev() concurrent safe")
CC: Keith Busch <kbusch@kernel.org>
Change-Id: I7cee1123c90ce184661470dcafab45cec919bc72
Signed-off-by: Shay Drory <shayd@nvidia.com>

---
changes from v1:
- add pci_iov_scan_device() helper (Bjorn)
---
 drivers/pci/iov.c | 47 +++++++++++++++++++++++++++++++++--------------
 1 file changed, 33 insertions(+), 14 deletions(-)

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 9e4770cdd4d5..9f08df0e7208 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -285,23 +285,16 @@ const struct attribute_group sriov_vf_dev_attr_group = {
 	.is_visible = sriov_vf_attrs_are_visible,
 };
 
-int pci_iov_add_virtfn(struct pci_dev *dev, int id)
+static struct pci_dev *pci_iov_scan_device(struct pci_dev *dev, int id,
+					   struct pci_bus *bus)
 {
-	int i;
-	int rc = -ENOMEM;
-	u64 size;
-	struct pci_dev *virtfn;
-	struct resource *res;
 	struct pci_sriov *iov = dev->sriov;
-	struct pci_bus *bus;
-
-	bus = virtfn_add_bus(dev->bus, pci_iov_virtfn_bus(dev, id));
-	if (!bus)
-		goto failed;
+	struct pci_dev *virtfn;
+	int rc = -ENOMEM;
 
 	virtfn = pci_alloc_dev(bus);
 	if (!virtfn)
-		goto failed0;
+		return ERR_PTR(rc);
 
 	virtfn->devfn = pci_iov_virtfn_devfn(dev, id);
 	virtfn->vendor = dev->vendor;
@@ -314,8 +307,34 @@ int pci_iov_add_virtfn(struct pci_dev *dev, int id)
 		pci_read_vf_config_common(virtfn);
 
 	rc = pci_setup_device(virtfn);
-	if (rc)
-		goto failed1;
+	if (rc) {
+		pci_dev_put(dev);
+		pci_bus_put(virtfn->bus);
+		kfree(virtfn);
+		return ERR_PTR(rc);
+	}
+
+	return virtfn;
+}
+
+int pci_iov_add_virtfn(struct pci_dev *dev, int id)
+{
+	int i;
+	int rc = -ENOMEM;
+	u64 size;
+	struct pci_dev *virtfn;
+	struct resource *res;
+	struct pci_bus *bus;
+
+	bus = virtfn_add_bus(dev->bus, pci_iov_virtfn_bus(dev, id));
+	if (!bus)
+		goto failed;
+
+	virtfn = pci_iov_scan_device(dev, id, bus);
+	if (IS_ERR(virtfn)) {
+		rc = PTR_ERR(virtfn);
+		goto failed0;
+	}
 
 	virtfn->dev.parent = dev->dev.parent;
 	virtfn->multifunction = 0;
-- 
2.38.1