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    Subject[PATCH 3/3] ipc: convert kern_ipc_perm.refcount 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>
    ---
    include/linux/ipc.h | 3 ++-
    ipc/util.c | 6 +++---
    2 files changed, 5 insertions(+), 4 deletions(-)

    diff --git a/include/linux/ipc.h b/include/linux/ipc.h
    index fadd579..ae68980 100644
    --- a/include/linux/ipc.h
    +++ b/include/linux/ipc.h
    @@ -4,6 +4,7 @@
    #include <linux/spinlock.h>
    #include <linux/uidgid.h>
    #include <uapi/linux/ipc.h>
    +#include <linux/refcount.h>

    #define IPCMNI 32768 /* <= MAX_INT limit for ipc arrays (including sysctl changes) */

    @@ -22,7 +23,7 @@ struct kern_ipc_perm {
    void *security;

    struct rcu_head rcu;
    - atomic_t refcount;
    + refcount_t refcount;
    } ____cacheline_aligned_in_smp __randomize_layout;

    #endif /* _LINUX_IPC_H */
    diff --git a/ipc/util.c b/ipc/util.c
    index 1a2cb02..069bb22 100644
    --- a/ipc/util.c
    +++ b/ipc/util.c
    @@ -232,7 +232,7 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size)

    idr_preload(GFP_KERNEL);

    - atomic_set(&new->refcount, 1);
    + refcount_set(&new->refcount, 1);
    spin_lock_init(&new->lock);
    new->deleted = false;
    rcu_read_lock();
    @@ -397,13 +397,13 @@ void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)

    int ipc_rcu_getref(struct kern_ipc_perm *ptr)
    {
    - return atomic_inc_not_zero(&ptr->refcount);
    + return refcount_inc_not_zero(&ptr->refcount);
    }

    void ipc_rcu_putref(struct kern_ipc_perm *ptr,
    void (*func)(struct rcu_head *head))
    {
    - if (!atomic_dec_and_test(&ptr->refcount))
    + if (!refcount_dec_and_test(&ptr->refcount))
    return;

    call_rcu(&ptr->rcu, func);
    --
    2.7.4
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