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    Subject[PATCH 1/2] security: create task_free security callback
    The current LSM interface to cred_free is not sufficient for allowing
    an LSM to track the life and death of a task. This patch adds the
    task_free hook so that an LSM can clean up resources on task death.

    Signed-off-by: Kees Cook <kees.cook@canonical.com>
    ---
    include/linux/security.h | 8 ++++++++
    kernel/fork.c | 1 +
    security/capability.c | 4 ++++
    security/security.c | 5 +++++
    4 files changed, 18 insertions(+), 0 deletions(-)

    diff --git a/include/linux/security.h b/include/linux/security.h
    index 723a93d..8007495 100644
    --- a/include/linux/security.h
    +++ b/include/linux/security.h
    @@ -637,6 +637,9 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
    * manual page for definitions of the @clone_flags.
    * @clone_flags contains the flags indicating what should be shared.
    * Return 0 if permission is granted.
    + * @task_free:
    + * @task task being freed
    + * Handle release of task-related resources.
    * @cred_alloc_blank:
    * @cred points to the credentials.
    * @gfp indicates the atomicity of any memory allocations.
    @@ -1481,6 +1484,7 @@ struct security_operations {
    int (*dentry_open) (struct file *file, const struct cred *cred);

    int (*task_create) (unsigned long clone_flags);
    + void (*task_free) (struct task_struct *task);
    int (*cred_alloc_blank) (struct cred *cred, gfp_t gfp);
    void (*cred_free) (struct cred *cred);
    int (*cred_prepare)(struct cred *new, const struct cred *old,
    @@ -1732,6 +1736,7 @@ int security_file_send_sigiotask(struct task_struct *tsk,
    int security_file_receive(struct file *file);
    int security_dentry_open(struct file *file, const struct cred *cred);
    int security_task_create(unsigned long clone_flags);
    +void security_task_free(struct task_struct *task);
    int security_cred_alloc_blank(struct cred *cred, gfp_t gfp);
    void security_cred_free(struct cred *cred);
    int security_prepare_creds(struct cred *new, const struct cred *old, gfp_t gfp);
    @@ -2232,6 +2237,9 @@ static inline int security_task_create(unsigned long clone_flags)
    return 0;
    }

    +static inline int security_task_free(struct task_struct *task)
    +{ }
    +
    static inline int security_cred_alloc_blank(struct cred *cred, gfp_t gfp)
    {
    return 0;
    diff --git a/kernel/fork.c b/kernel/fork.c
    index b6cce14..7fbc5e3 100644
    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -183,6 +183,7 @@ void __put_task_struct(struct task_struct *tsk)
    WARN_ON(atomic_read(&tsk->usage));
    WARN_ON(tsk == current);

    + security_task_free(tsk);
    exit_creds(tsk);
    delayacct_tsk_free(tsk);
    put_signal_struct(tsk->signal);
    diff --git a/security/capability.c b/security/capability.c
    index 4aeb699..3649d4b 100644
    --- a/security/capability.c
    +++ b/security/capability.c
    @@ -353,6 +353,9 @@ static int cap_task_create(unsigned long clone_flags)
    return 0;
    }

    +static void cap_task_free(struct task_struct *task)
    +{ }
    +
    static int cap_cred_alloc_blank(struct cred *cred, gfp_t gfp)
    {
    return 0;
    @@ -936,6 +939,7 @@ void __init security_fixup_ops(struct security_operations *ops)
    set_to_cap_if_null(ops, file_receive);
    set_to_cap_if_null(ops, dentry_open);
    set_to_cap_if_null(ops, task_create);
    + set_to_cap_if_null(ops, task_free);
    set_to_cap_if_null(ops, cred_alloc_blank);
    set_to_cap_if_null(ops, cred_free);
    set_to_cap_if_null(ops, cred_prepare);
    diff --git a/security/security.c b/security/security.c
    index e8c87b8..103c35f 100644
    --- a/security/security.c
    +++ b/security/security.c
    @@ -691,6 +691,11 @@ int security_task_create(unsigned long clone_flags)
    return security_ops->task_create(clone_flags);
    }

    +void security_task_free(struct task_struct *task)
    +{
    + security_ops->task_free(task);
    +}
    +
    int security_cred_alloc_blank(struct cred *cred, gfp_t gfp)
    {
    return security_ops->cred_alloc_blank(cred, gfp);
    --
    1.7.1

    --
    Kees Cook
    Ubuntu Security Team


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