Received-SPF: pass (google.com: domain of linux-nfs-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Jeff Moyer <jmoyer@redhat.com>
To:     Frederick Lawler <fred@cloudflare.com>
Cc:     linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-aio@kvack.org, linux-fsdevel@vger.kernel.org,
        linux-cachefs@redhat.com, linux-cifs@vger.kernel.org,
        samba-technical@lists.samba.org, linux-mm@kvack.org,
        linux-nfs@vger.kernel.org, linux-unionfs@vger.kernel.org,
        linux-security-module@vger.kernel.org, netdev@vger.kernel.org,
        keyrings@vger.kernel.org, selinux@vger.kernel.org,
        serge@hallyn.com, amir73il@gmail.com, kernel-team@cloudflare.com
Subject: Re: [PATCH v2] cred: Propagate security_prepare_creds() error code
References: <20220525183703.466936-1-fred@cloudflare.com>
Date:   Thu, 26 May 2022 16:43:44 -0400
In-Reply-To: <20220525183703.466936-1-fred@cloudflare.com> (Frederick Lawler's
        message of "Wed, 25 May 2022 13:37:03 -0500")
Message-ID: <x49o7zkvxbz.fsf@segfault.boston.devel.redhat.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Frederick Lawler <fred@cloudflare.com> writes:

> While experimenting with the security_prepare_creds() LSM hook, we
> noticed that our EPERM error code was not propagated up the callstack.
> Instead ENOMEM is always returned.  As a result, some tools may send a
> confusing error message to the user:
>
> $ unshare -rU
> unshare: unshare failed: Cannot allocate memory
>
> A user would think that the system didn't have enough memory, when
> instead the action was denied.
>
> This problem occurs because prepare_creds() and prepare_kernel_cred()
> return NULL when security_prepare_creds() returns an error code. Later,
> functions calling prepare_creds() and prepare_kernel_cred() return
> ENOMEM because they assume that a NULL meant there was no memory
> allocated.
>
> Fix this by propagating an error code from security_prepare_creds() up
> the callstack.
>
> Signed-off-by: Frederick Lawler <fred@cloudflare.com>

The fs/aio.c part looks ok to me.  We should probably also update the
man page for io_submit, though, to document the conditions under which
EPERM can be returned.

Acked-by: Jeff Moyer <jmoyer@redhat.com>