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    Subject[PATCH 3.2 058/107] IB/uverbs: Fix race between ib_uverbs_open and remove_one
    3.2.72-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Yishai Hadas <yishaih@mellanox.com>

    commit 35d4a0b63dc0c6d1177d4f532a9deae958f0662c upstream.

    Fixes: 2a72f212263701b927559f6850446421d5906c41 ("IB/uverbs: Remove dev_table")

    Before this commit there was a device look-up table that was protected
    by a spin_lock used by ib_uverbs_open and by ib_uverbs_remove_one. When
    it was dropped and container_of was used instead, it enabled the race
    with remove_one as dev might be freed just after:
    dev = container_of(inode->i_cdev, struct ib_uverbs_device, cdev) but
    before the kref_get.

    In addition, this buggy patch added some dead code as
    container_of(x,y,z) can never be NULL and so dev can never be NULL.
    As a result the comment above ib_uverbs_open saying "the open method
    will either immediately run -ENXIO" is wrong as it can never happen.

    The solution follows Jason Gunthorpe suggestion from below URL:
    https://www.mail-archive.com/linux-rdma@vger.kernel.org/msg25692.html

    cdev will hold a kref on the parent (the containing structure,
    ib_uverbs_device) and only when that kref is released it is
    guaranteed that open will never be called again.

    In addition, fixes the active count scheme to use an atomic
    not a kref to prevent WARN_ON as pointed by above comment
    from Jason.

    Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
    Signed-off-by: Shachar Raindel <raindel@mellanox.com>
    Reviewed-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
    Signed-off-by: Doug Ledford <dledford@redhat.com>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/infiniband/core/uverbs.h | 3 ++-
    drivers/infiniband/core/uverbs_main.c | 43 ++++++++++++++++++++++++-----------
    2 files changed, 32 insertions(+), 14 deletions(-)

    --- a/drivers/infiniband/core/uverbs.h
    +++ b/drivers/infiniband/core/uverbs.h
    @@ -69,7 +69,7 @@
    */

    struct ib_uverbs_device {
    - struct kref ref;
    + atomic_t refcount;
    int num_comp_vectors;
    struct completion comp;
    struct device *dev;
    @@ -78,6 +78,7 @@ struct ib_uverbs_device {
    struct cdev cdev;
    struct rb_root xrcd_tree;
    struct mutex xrcd_tree_mutex;
    + struct kobject kobj;
    };

    struct ib_uverbs_event_file {
    --- a/drivers/infiniband/core/uverbs_main.c
    +++ b/drivers/infiniband/core/uverbs_main.c
    @@ -117,14 +117,18 @@ static ssize_t (*uverbs_cmd_table[])(str
    static void ib_uverbs_add_one(struct ib_device *device);
    static void ib_uverbs_remove_one(struct ib_device *device);

    -static void ib_uverbs_release_dev(struct kref *ref)
    +static void ib_uverbs_release_dev(struct kobject *kobj)
    {
    struct ib_uverbs_device *dev =
    - container_of(ref, struct ib_uverbs_device, ref);
    + container_of(kobj, struct ib_uverbs_device, kobj);

    - complete(&dev->comp);
    + kfree(dev);
    }

    +static struct kobj_type ib_uverbs_dev_ktype = {
    + .release = ib_uverbs_release_dev,
    +};
    +
    static void ib_uverbs_release_event_file(struct kref *ref)
    {
    struct ib_uverbs_event_file *file =
    @@ -273,13 +277,19 @@ static int ib_uverbs_cleanup_ucontext(st
    return context->device->dealloc_ucontext(context);
    }

    +static void ib_uverbs_comp_dev(struct ib_uverbs_device *dev)
    +{
    + complete(&dev->comp);
    +}
    +
    static void ib_uverbs_release_file(struct kref *ref)
    {
    struct ib_uverbs_file *file =
    container_of(ref, struct ib_uverbs_file, ref);

    module_put(file->device->ib_dev->owner);
    - kref_put(&file->device->ref, ib_uverbs_release_dev);
    + if (atomic_dec_and_test(&file->device->refcount))
    + ib_uverbs_comp_dev(file->device);

    kfree(file);
    }
    @@ -621,9 +631,7 @@ static int ib_uverbs_open(struct inode *
    int ret;

    dev = container_of(inode->i_cdev, struct ib_uverbs_device, cdev);
    - if (dev)
    - kref_get(&dev->ref);
    - else
    + if (!atomic_inc_not_zero(&dev->refcount))
    return -ENXIO;

    if (!try_module_get(dev->ib_dev->owner)) {
    @@ -644,6 +652,7 @@ static int ib_uverbs_open(struct inode *
    mutex_init(&file->mutex);

    filp->private_data = file;
    + kobject_get(&dev->kobj);

    return nonseekable_open(inode, filp);

    @@ -651,13 +660,16 @@ err_module:
    module_put(dev->ib_dev->owner);

    err:
    - kref_put(&dev->ref, ib_uverbs_release_dev);
    + if (atomic_dec_and_test(&dev->refcount))
    + ib_uverbs_comp_dev(dev);
    +
    return ret;
    }

    static int ib_uverbs_close(struct inode *inode, struct file *filp)
    {
    struct ib_uverbs_file *file = filp->private_data;
    + struct ib_uverbs_device *dev = file->device;

    ib_uverbs_cleanup_ucontext(file, file->ucontext);

    @@ -665,6 +677,7 @@ static int ib_uverbs_close(struct inode
    kref_put(&file->async_file->ref, ib_uverbs_release_event_file);

    kref_put(&file->ref, ib_uverbs_release_file);
    + kobject_put(&dev->kobj);

    return 0;
    }
    @@ -760,10 +773,11 @@ static void ib_uverbs_add_one(struct ib_
    if (!uverbs_dev)
    return;

    - kref_init(&uverbs_dev->ref);
    + atomic_set(&uverbs_dev->refcount, 1);
    init_completion(&uverbs_dev->comp);
    uverbs_dev->xrcd_tree = RB_ROOT;
    mutex_init(&uverbs_dev->xrcd_tree_mutex);
    + kobject_init(&uverbs_dev->kobj, &ib_uverbs_dev_ktype);

    spin_lock(&map_lock);
    devnum = find_first_zero_bit(dev_map, IB_UVERBS_MAX_DEVICES);
    @@ -790,6 +804,7 @@ static void ib_uverbs_add_one(struct ib_
    cdev_init(&uverbs_dev->cdev, NULL);
    uverbs_dev->cdev.owner = THIS_MODULE;
    uverbs_dev->cdev.ops = device->mmap ? &uverbs_mmap_fops : &uverbs_fops;
    + uverbs_dev->cdev.kobj.parent = &uverbs_dev->kobj;
    kobject_set_name(&uverbs_dev->cdev.kobj, "uverbs%d", uverbs_dev->devnum);
    if (cdev_add(&uverbs_dev->cdev, base, 1))
    goto err_cdev;
    @@ -820,9 +835,10 @@ err_cdev:
    clear_bit(devnum, overflow_map);

    err:
    - kref_put(&uverbs_dev->ref, ib_uverbs_release_dev);
    + if (atomic_dec_and_test(&uverbs_dev->refcount))
    + ib_uverbs_comp_dev(uverbs_dev);
    wait_for_completion(&uverbs_dev->comp);
    - kfree(uverbs_dev);
    + kobject_put(&uverbs_dev->kobj);
    return;
    }

    @@ -842,9 +858,10 @@ static void ib_uverbs_remove_one(struct
    else
    clear_bit(uverbs_dev->devnum - IB_UVERBS_MAX_DEVICES, overflow_map);

    - kref_put(&uverbs_dev->ref, ib_uverbs_release_dev);
    + if (atomic_dec_and_test(&uverbs_dev->refcount))
    + ib_uverbs_comp_dev(uverbs_dev);
    wait_for_completion(&uverbs_dev->comp);
    - kfree(uverbs_dev);
    + kobject_put(&uverbs_dev->kobj);
    }

    static char *uverbs_devnode(struct device *dev, mode_t *mode)


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