From 2a671f77ee49f3e78997b77fdee139467ff6a598 Mon Sep 17 00:00:00 2001 From: Niklas Schnelle Date: Fri, 6 Aug 2021 12:11:16 +0200 Subject: [PATCH] s390/pci: fix use after free of zpci_dev 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 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: 05bc1be6db4b2 ("s390/pci: create zPCI bus") Cc: stable@vger.kernel.org Reviewed-by: Matthew Rosato Signed-off-by: Niklas Schnelle Signed-off-by: Vasily Gorbik --- 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 b0993e05affe65..8fcb7ecb7225ad 100644 --- a/arch/s390/pci/pci.c +++ b/arch/s390/pci/pci.c @@ -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) diff --git a/arch/s390/pci/pci_bus.h b/arch/s390/pci/pci_bus.h index b877a97e6745bc..e359d2686178b8 100644 --- a/arch/s390/pci/pci_bus.h +++ b/arch/s390/pci/pci_bus.h @@ -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,