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    SubjectRe: [PATCH 020/190] Revert "PCI: Fix pci_create_slot() reference count leak"
    [+cc Jiri, Jubin (author of 4684709bf81a)]

    On Wed, Apr 21, 2021 at 02:58:15PM +0200, Greg Kroah-Hartman wrote:
    > This reverts commit 8a94644b440eef5a7b9c104ac8aa7a7f413e35e5.
    >
    > Commits from @umn.edu addresses have been found to be submitted in "bad
    > faith" to try to test the kernel community's ability to review "known
    > malicious" changes. The result of these submissions can be found in a
    > paper published at the 42nd IEEE Symposium on Security and Privacy
    > entitled, "Open Source Insecurity: Stealthily Introducing
    > Vulnerabilities via Hypocrite Commits" written by Qiushi Wu (University
    > of Minnesota) and Kangjie Lu (University of Minnesota).
    >
    > Because of this, all submissions from this group must be reverted from
    > the kernel tree and will need to be re-reviewed again to determine if
    > they actually are a valid fix. Until that work is complete, remove this
    > change to ensure that no problems are being introduced into the
    > codebase.
    >
    > Cc: https
    > Cc: Qiushi Wu <wu000273@umn.edu>
    > Cc: Bjorn Helgaas <bhelgaas@google.com>
    > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    Please do not apply this revert.

    Prior to 8a94644b440e ("PCI: Fix pci_create_slot() reference count
    leak"), we essentially had this:

    err = kobject_init_and_add(&slot->kobj, &pci_slot_ktype, ...);
    if (err)
    kfree(slot);
    return ERR_PTR(err);

    INIT_LIST_HEAD(&slot->list);
    list_add(&slot->list, &parent->slots);

    That was incorrect because if kobject_init_and_add() fails,
    kobject_put() must be called to clean up the object (per the function
    comment). For pci_slot_ktype, the release function is
    pci_slot_release():

    pci_slot_release
    list_del(&slot->list);
    kfree(slot);

    After 8a94644b440e, we had:

    err = kobject_init_and_add(&slot->kobj, &pci_slot_ktype, ...);
    if (err)
    kobject_put(&slot->kobj);
    return ERR_PTR(err);

    INIT_LIST_HEAD(&slot->list);
    list_add(&slot->list, &parent->slots);

    This fixed one bug but exposed another: we correctly clean up the
    object by calling kobject_put() which calls pci_slot_release(), but
    that dereferences slot->list, which hasn't been initialized yet.

    But 4684709bf81a ("PCI: Fix pci_slot_release() NULL pointer
    dereference") fixed that problem by making it this:

    INIT_LIST_HEAD(&slot->list);
    list_add(&slot->list, &parent->slots);
    err = kobject_init_and_add(&slot->kobj, &pci_slot_ktype, ...);
    if (err)
    kobject_put(&slot->kobj);
    return ERR_PTR(err);

    This correctly initializes slot->list and cleans up if
    kobject_init_and_add() fails.

    But if we apply this revert, we'll have this:

    INIT_LIST_HEAD(&slot->list);
    list_add(&slot->list, &parent->slots);
    err = kobject_init_and_add(&slot->kobj, &pci_slot_ktype, ...);
    if (err)
    kfree(slot);
    return ERR_PTR(err);

    Now we kfree(slot), but we don't call kobject_put(), so we don't
    remove it from the list, so the list is now corrupted because one of
    its entries has been deallocated.

    Bjorn

    > ---
    > drivers/pci/slot.c | 6 ++----
    > 1 file changed, 2 insertions(+), 4 deletions(-)
    >
    > diff --git a/drivers/pci/slot.c b/drivers/pci/slot.c
    > index d627dd9179b4..c190e09af356 100644
    > --- a/drivers/pci/slot.c
    > +++ b/drivers/pci/slot.c
    > @@ -268,7 +268,6 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr,
    > slot_name = make_slot_name(name);
    > if (!slot_name) {
    > err = -ENOMEM;
    > - kfree(slot);
    > goto err;
    > }
    >
    > @@ -277,10 +276,8 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr,
    >
    > err = kobject_init_and_add(&slot->kobj, &pci_slot_ktype, NULL,
    > "%s", slot_name);
    > - if (err) {
    > - kobject_put(&slot->kobj);
    > + if (err)
    > goto err;
    > - }
    >
    > down_read(&pci_bus_sem);
    > list_for_each_entry(dev, &parent->devices, bus_list)
    > @@ -296,6 +293,7 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr,
    > mutex_unlock(&pci_slot_mutex);
    > return slot;
    > err:
    > + kfree(slot);
    > slot = ERR_PTR(err);
    > goto out;
    > }
    > --
    > 2.31.1
    >

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