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s390/pci: fix use after free of zpci_dev

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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 0b13525c20
("s390/pci: fix leak of PCI device structure") exposing the broken
behavior.

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: 05bc1be6db ("s390/pci: create zPCI bus")
Cc: stable@vger.kernel.org
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
This commit is contained in:
Niklas Schnelle 2021-08-06 12:11:16 +02:00 committed by Vasily Gorbik
parent 7c60610d47
commit 2a671f77ee
2 changed files with 11 additions and 0 deletions
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6
arch/s390/pci/pci.c
View file

@ -560,9 +560,12 @@ 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;
@ -582,7 +585,10 @@ int pcibios_add_device(struct pci_dev *pdev)
void pcibios_release_device(struct pci_dev *pdev)
{
struct zpci_dev *zdev = to_zpci(pdev);
zpci_unmap_resources(pdev);
zpci_zdev_put(zdev);
}
int pcibios_enable_device(struct pci_dev *pdev, int mask)

5
arch/s390/pci/pci_bus.h
View file

@ -22,6 +22,11 @@ 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,