Re: [RFC PATCH ghak90 (was ghak32) V3 09/10] debug audit: read container ID of a process

[Paul Moore <paul@paul-moore.com>]

On Wed, Jun 6, 2018 at 1:02 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> Add support for reading the audit container identifier from the proc
> filesystem.
>
> This is a read from the proc entry of the form
> /proc/PID/audit_containerid where PID is the process ID of the task
> whose audit container identifier is sought.
>
> The read expects up to a u64 value (unset: 18446744073709551615).
>
> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> ---
>  fs/proc/base.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 318dff4..ca8bfe2 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1303,6 +1303,21 @@ static ssize_t proc_sessionid_read(struct file * file, char __user * buf,
>         .llseek         = generic_file_llseek,
>  };
>
> +static ssize_t proc_contid_read(struct file *file, char __user *buf,
> +                                 size_t count, loff_t *ppos)
> +{
> +       struct inode *inode = file_inode(file);
> +       struct task_struct *task = get_proc_task(inode);
> +       ssize_t length;
> +       char tmpbuf[TMPBUFLEN*2];
> +
> +       if (!task)
> +               return -ESRCH;
> +       length = scnprintf(tmpbuf, TMPBUFLEN*2, "%llu", audit_get_contid(task));
> +       put_task_struct(task);
> +       return simple_read_from_buffer(buf, count, ppos, tmpbuf, length);
> +}

While I still remain very nervous about opening the audit container ID
up for abuse by making it accessible, I understand that this would
make things a lot easier us (e.g. testing) and perhaps the container
engines as well.  In order to limit the potential for abuse, what do
you think about restricting read access to those processes which have
CAP_AUDIT_CONTROL, similar to what we do for setting the audit
container ID?

>  static ssize_t proc_contid_write(struct file *file, const char __user *buf,
>                                    size_t count, loff_t *ppos)
>  {
> @@ -1333,6 +1348,7 @@ static ssize_t proc_contid_write(struct file *file, const char __user *buf,
>  }
>
>  static const struct file_operations proc_contid_operations = {
> +       .read           = proc_contid_read,
>         .write          = proc_contid_write,
>         .llseek         = generic_file_llseek,
>  };
> @@ -3030,7 +3046,7 @@ static int proc_pid_patch_state(struct seq_file *m, struct pid_namespace *ns,
>  #ifdef CONFIG_AUDITSYSCALL
>         REG("loginuid",   S_IWUSR|S_IRUGO, proc_loginuid_operations),
>         REG("sessionid",  S_IRUGO, proc_sessionid_operations),
> -       REG("audit_containerid", S_IWUSR, proc_contid_operations),
> +       REG("audit_containerid", S_IWUSR|S_IRUSR, proc_contid_operations),
>  #endif
>  #ifdef CONFIG_FAULT_INJECTION
>         REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations),
> @@ -3422,7 +3438,7 @@ static int proc_tid_comm_permission(struct inode *inode, int mask)
>  #ifdef CONFIG_AUDITSYSCALL
>         REG("loginuid",  S_IWUSR|S_IRUGO, proc_loginuid_operations),
>         REG("sessionid",  S_IRUGO, proc_sessionid_operations),
> -       REG("audit_containerid", S_IWUSR, proc_contid_operations),
> +       REG("audit_containerid", S_IWUSR|S_IRUSR, proc_contid_operations),
>  #endif
>  #ifdef CONFIG_FAULT_INJECTION
>         REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations),

--
paul moore
www.paul-moore.com