[PATCH 3.4 21/92] IB/uverbs: Fix race between ib_uverbs_open and remove_one

lizf
2016-04-18T10:48:08Z

From: Yishai Hadas <yishaih@mellanox.com>

3.4.112-rc1 review patch. If anyone has any objections, please let me know.

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

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: Zefan Li <lizefan@huawei.com>
---
drivers/infiniband/core/uverbs.h | 3 ++-
drivers/infiniband/core/uverbs_main.c | 43 ++++++++++++++++++++++++-----------
2 files changed, 32 insertions(+), 14 deletions(-)

diff --git a/drivers/infiniband/core/uverbs.h b/drivers/infiniband/core/uverbs.h
index 5bcb2af..228af18 100644
--- 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 {
diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index 5b51e4e..c8e7669 100644
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -117,14 +117,18 @@ static ssize_t (*uverbs_cmd_table[])(struct ib_uverbs_file *file,
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(struct ib_uverbs_file *file,
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 *inode, struct file *filp)
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 *inode, struct file *filp)
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 *inode, struct file *filp)
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_device *device)
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_device *device)
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 ib_device *device)
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, umode_t *mode)
--
1.9.1