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    Subject[PATCH 07/29] drivers, md: convert dm_dev_internal.count from atomic_t to refcount_t
    Date
    refcount_t type and corresponding API should be
    used instead of atomic_t when the variable is used as
    a reference counter. This allows to avoid accidental
    refcounter overflows that might lead to use-after-free
    situations.

    Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
    Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
    Signed-off-by: Kees Cook <keescook@chromium.org>
    Signed-off-by: David Windsor <dwindsor@gmail.com>
    ---
    drivers/md/dm-table.c | 6 +++---
    drivers/md/dm.h | 3 ++-
    2 files changed, 5 insertions(+), 4 deletions(-)

    diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
    index 3ad16d9..d2e2741 100644
    --- a/drivers/md/dm-table.c
    +++ b/drivers/md/dm-table.c
    @@ -416,15 +416,15 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
    return r;
    }

    - atomic_set(&dd->count, 0);
    + refcount_set(&dd->count, 1);
    list_add(&dd->list, &t->devices);

    } else if (dd->dm_dev->mode != (mode | dd->dm_dev->mode)) {
    r = upgrade_mode(dd, mode, t->md);
    if (r)
    return r;
    + refcount_inc(&dd->count);
    }
    - atomic_inc(&dd->count);

    *result = dd->dm_dev;
    return 0;
    @@ -478,7 +478,7 @@ void dm_put_device(struct dm_target *ti, struct dm_dev *d)
    dm_device_name(ti->table->md), d->name);
    return;
    }
    - if (atomic_dec_and_test(&dd->count)) {
    + if (refcount_dec_and_test(&dd->count)) {
    dm_put_table_device(ti->table->md, d);
    list_del(&dd->list);
    kfree(dd);
    diff --git a/drivers/md/dm.h b/drivers/md/dm.h
    index f298b01..63b8142 100644
    --- a/drivers/md/dm.h
    +++ b/drivers/md/dm.h
    @@ -19,6 +19,7 @@
    #include <linux/hdreg.h>
    #include <linux/completion.h>
    #include <linux/kobject.h>
    +#include <linux/refcount.h>

    #include "dm-stats.h"

    @@ -38,7 +39,7 @@
    */
    struct dm_dev_internal {
    struct list_head list;
    - atomic_t count;
    + refcount_t count;
    struct dm_dev *dm_dev;
    };

    --
    2.7.4
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