[PATCH 5.10 90/98] s390/pci: fix use after free of zpci_dev

From: Sasha Levin
Date: Tue Aug 24 2021 - 13:13:17 EST

From: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>

[ Upstream commit 2a671f77ee49f3e78997b77fdee139467ff6a598 ]

The struct pci_dev uses reference counting but zPCI assumed erroneously
that the last reference would always be the local reference after
calling pci_stop_and_remove_bus_device(). This is usually the case but
not how reference counting works and thus inherently fragile.

In fact one case where this causes a NULL pointer dereference when on an
SRIOV device the function 0 was hot unplugged before another function of
the same multi-function device. In this case the second function's
pdev->sriov->dev reference keeps the struct pci_dev of function 0 alive
even after the unplug. This bug was previously hidden by the fact that
we were leaking the struct pci_dev which in turn means that it always
outlived the struct zpci_dev. This was fixed in commit 0b13525c20fe
("s390/pci: fix leak of PCI device structure") exposing the broken

Fix this by accounting for the long living reference a struct pci_dev
has to its underlying struct zpci_dev via the zbus->function[] array and
only release that in pcibios_release_device() ensuring that the struct
pci_dev is not left with a dangling reference. This is a minimal fix in
the future it would probably better to use fine grained reference
counting for struct zpci_dev.

Fixes: 05bc1be6db4b2 ("s390/pci: create zPCI bus")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
arch/s390/pci/pci.c | 6 ++++++
arch/s390/pci/pci_bus.h | 5 +++++
2 files changed, 11 insertions(+)

diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
index 1ae7a76ae97b..ca1a105e3b5d 100644
--- a/arch/s390/pci/pci.c
+++ b/arch/s390/pci/pci.c
@@ -558,9 +558,12 @@ static void zpci_cleanup_bus_resources(struct zpci_dev *zdev)

int pcibios_add_device(struct pci_dev *pdev)
+ struct zpci_dev *zdev = to_zpci(pdev);
struct resource *res;
int i;

+ /* The pdev has a reference to the zdev via its bus */
+ zpci_zdev_get(zdev);
if (pdev->is_physfn)
pdev->no_vf_scan = 1;

@@ -580,7 +583,10 @@ int pcibios_add_device(struct pci_dev *pdev)

void pcibios_release_device(struct pci_dev *pdev)
+ struct zpci_dev *zdev = to_zpci(pdev);
+ zpci_zdev_put(zdev);

int pcibios_enable_device(struct pci_dev *pdev, int mask)
diff --git a/arch/s390/pci/pci_bus.h b/arch/s390/pci/pci_bus.h
index f8dfac0b5b71..55c9488e504c 100644
--- a/arch/s390/pci/pci_bus.h
+++ b/arch/s390/pci/pci_bus.h
@@ -16,6 +16,11 @@ static inline void zpci_zdev_put(struct zpci_dev *zdev)
kref_put(&zdev->kref, zpci_release_device);

+static inline void zpci_zdev_get(struct zpci_dev *zdev)
+ kref_get(&zdev->kref);
int zpci_alloc_domain(int domain);
void zpci_free_domain(int domain);
int zpci_setup_bus_resources(struct zpci_dev *zdev,