Re: [Linux-cachefs] [PATCH v3] cred: Propagate security_prepare_creds() error code

[Eric Biggers]

On Wed, Jun 08, 2022 at 10:09:42AM -0500, Frederick Lawler wrote:
> diff --git a/fs/aio.c b/fs/aio.c
> index 3c249b938632..5abbe88c3ca7 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -1620,6 +1620,8 @@ static void aio_fsync_work(struct work_struct *work)
>  static int aio_fsync(struct fsync_iocb *req, const struct iocb *iocb,
>                    bool datasync)
>  {
> +     int err;
> +
>       if (unlikely(iocb->aio_buf || iocb->aio_offset || iocb->aio_nbytes ||
>                       iocb->aio_rw_flags))
>               return -EINVAL;
> @@ -1628,8 +1630,11 @@ static int aio_fsync(struct fsync_iocb *req, const 
> struct iocb *iocb,
>               return -EINVAL;
>  
>       req->creds = prepare_creds();
> -     if (!req->creds)
> -             return -ENOMEM;
> +     if (IS_ERR(req->creds)) {
> +             err = PTR_ERR(req->creds);
> +             req->creds = NULL;
> +             return err;
> +     }

This part is a little ugly.  How about doing:

        creds = prepare_creds();
        if (IS_ERR(creds))
                return PTR_ERR(creds);
        req->creds = creds;

> diff --git a/fs/exec.c b/fs/exec.c
> index 0989fb8472a1..02624783e40e 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1468,15 +1468,19 @@ EXPORT_SYMBOL(finalize_exec);
>   */
>  static int prepare_bprm_creds(struct linux_binprm *bprm)
>  {
> +     int err = -ERESTARTNOINTR;
>       if (mutex_lock_interruptible(&current->signal->cred_guard_mutex))
> -             return -ERESTARTNOINTR;
> +             return err;
>  
>       bprm->cred = prepare_exec_creds();
> -     if (likely(bprm->cred))
> -             return 0;
> +     if (IS_ERR(bprm->cred)) {
> +             err = PTR_ERR(bprm->cred);
> +             bprm->cred = NULL;
> +             mutex_unlock(&current->signal->cred_guard_mutex);
> +             return err;
> +     }
>  
> -     mutex_unlock(&current->signal->cred_guard_mutex);
> -     return -ENOMEM;
> +     return 0;
>  }

Similarly:

static int prepare_bprm_creds(struct linux_binprm *bprm)
{
        struct cred *cred;

        if (mutex_lock_interruptible(&current->signal->cred_guard_mutex))
                return -ERESTARTNOINTR;

        cred = prepare_exec_creds();
        if (IS_ERR(cred)) {
                mutex_unlock(&current->signal->cred_guard_mutex);
                return PTR_ERR(cred);
        }
        bprm->cred = cred;
        return 0;
}

> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> index eec72ca962e2..6cf75aa83b6c 100644
> --- a/kernel/nsproxy.c
> +++ b/kernel/nsproxy.c
> @@ -311,6 +311,7 @@ static void put_nsset(struct nsset *nsset)
>  
>  static int prepare_nsset(unsigned flags, struct nsset *nsset)
>  {
> +     int err = -ENOMEM;
>       struct task_struct *me = current;
>  
>       nsset->nsproxy = create_new_namespaces(0, me, current_user_ns(), 
> me->fs);
> @@ -324,6 +325,12 @@ static int prepare_nsset(unsigned flags, struct nsset 
> *nsset)
>       if (!nsset->cred)
>               goto out;
>  
> +     if (IS_ERR(nsset->cred)) {
> +             err = PTR_ERR(nsset->cred);
> +             nsset->cred = NULL;
> +             goto out;
> +     }

Why is the NULL check above being kept?

Also, drivers/crypto/ccp/sev-dev.c needs to be updated.

- Eric

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