Re: [PATCH ghak81 RFC V1 3/5] audit: use inline function to get audit context

[Paul Moore]

On Fri, May 4, 2018 at 4:54 PM, Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> Recognizing that the audit context is an internal audit value, use an
> access function to retrieve the audit context pointer for the task
> rather than reaching directly into the task struct to get it.
>
> Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> ---
>  include/linux/audit.h                | 16 ++++++++---
>  include/net/xfrm.h                   |  2 +-
>  kernel/audit.c                       |  4 +--
>  kernel/audit_watch.c                 |  2 +-
>  kernel/auditsc.c                     | 52 ++++++++++++++++++------------------
>  net/bridge/netfilter/ebtables.c      |  2 +-
>  net/core/dev.c                       |  2 +-
>  net/netfilter/x_tables.c             |  2 +-
>  net/netlabel/netlabel_user.c         |  2 +-
>  security/integrity/ima/ima_api.c     |  2 +-
>  security/integrity/integrity_audit.c |  2 +-
>  security/lsm_audit.c                 |  2 +-
>  security/selinux/hooks.c             |  4 +--
>  security/selinux/selinuxfs.c         |  6 ++---
>  security/selinux/ss/services.c       | 12 ++++-----
>  15 files changed, 60 insertions(+), 52 deletions(-)
>
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index 5f86f7c..93e4c61 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -235,26 +235,30 @@ extern void __audit_inode_child(struct inode *parent,
>  extern void __audit_seccomp(unsigned long syscall, long signr, int code);
>  extern void __audit_ptrace(struct task_struct *t);
>
> +static inline struct audit_context *audit_context(struct task_struct *task)
> +{
> +       return task->audit_context;
> +}

Another case where I think I agree with everything here on principle,
especially when one considers it in the larger context of the audit
container ID work.  However, I think we might be able to somply this a
bit by eliminating the parameter to the new audit_context() helper and
making it always reference the current task_struct.  Based on this
patch it would appear that this change would work for all callers
except for audit_take_context() and __audit_syscall_entry(), both of
which are contained within the core audit code and are enough of a
special case that I think it is acceptable for them to access the
context directly.  I'm trying to think of reasons why a non-audit
kernel subsystem would ever need to access the audit context of a
process other than current and I can't think of any ... removing the
task_struct pointer might help prevent mistakes/abuse in the future.

> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 6e3ceb9..a4bbdcc 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -836,7 +836,7 @@ static inline struct audit_context *audit_take_context(struct task_struct *tsk,
>                                                       int return_valid,
>                                                       long return_code)
>  {
> -       struct audit_context *context = tsk->audit_context;
> +       struct audit_context *context = audit_context(tsk);
>
>         if (!context)
>                 return NULL;
> @@ -1510,7 +1510,7 @@ void __audit_syscall_entry(int major, unsigned long a1, unsigned long a2,
>                            unsigned long a3, unsigned long a4)
>  {
>         struct task_struct *tsk = current;
> -       struct audit_context *context = tsk->audit_context;
> +       struct audit_context *context = audit_context(tsk);
>         enum audit_state     state;
>
>         if (!audit_enabled || !context)

-- 
paul moore
www.paul-moore.com