linux-kernel - Re: [RFC PATCH v3 0/2] Add capabilities file to sysfs

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Message-ID: <6086103.nWTFFhADWI@machine>
Date:   Thu, 20 Jan 2022 19:14:16 +0100
From:   Francis Laniel <flaniel@...ux.microsoft.com>
To:     linux-kernel@...r.kernel.org,
        Casey Schaufler <casey@...aufler-ca.com>
Cc:     linux-security-module@...r.kernel.org,
        Serge Hallyn <serge@...lyn.com>
Subject: Re: [RFC PATCH v3 0/2] Add capabilities file to sysfs

Le jeudi 20 janvier 2022, 19:09:50 CET Casey Schaufler a écrit :
> On 1/20/2022 10:01 AM, Francis Laniel wrote:
> > Hi.
> > 
> > 
> > First, I hope you are fine and the same for your relatives.
> > 
> > Capabilities are used to check if a thread has the right to perform a
> > given
> > action [1].
> > For example, a thread with CAP_BPF set can use the bpf() syscall.
> > 
> > Capabilities are used in the container world.
> > In terms of code, several projects related to container maintain code
> > where the capabilities are written alike include/uapi/linux/capability.h
> > [2][3][4][5]. For these projects, their codebase should be updated when a
> > new capability is added to the kernel.
> > Some other projects rely on <sys/capability.h> [6].
> > In this case, this header file should reflect the capabilities offered by
> > the kernel.
> > 
> > So, in this series, I added a new file to sysfs:
> > /sys/kernel/security/capabilities.
> > The goal of this file is to be used by "container world" software to know
> > kernel capabilities at run time instead of compile time.
> > 
> > The "file" is read-only and its content is the capability number
> > associated with the capability name:
> > root@...amd64:~# cat /sys/kernel/security/capabilities
> > 0       CAP_CHOWN
> > 1       CAP_DAC_OVERRIDE
> > ...
> > 40      CAP_CHECKPOINT_RESTORE
> > 
> > The kernel already exposes the last capability number under:
> > /proc/sys/kernel/cap_last_cap
> > So, I think there should not be any issue exposing all the capabilities it
> > offers.
> > If there is any, please share it as I do not want to introduce issue with
> > this series.
> > 
> > Also, if you see any way to improve this series please share it as it
> > would
> > increase this contribution quality.
> > 
> > Change since v2:
> > * Use a char * for cap_string instead of an array, each line of this char
> > *
> > contains the capability number and its name.
> > * Move the file under /sys/kernel/security instead of /sys/kernel.
> > 
> > Francis Laniel (2):
> >    capability: Add cap_string.
> >    security/inode.c: Add capabilities file.
> >   
> >   include/uapi/linux/capability.h |  1 +
> >   kernel/capability.c             | 45 +++++++++++++++++++++++++++++++++
> >   security/inode.c                | 16 ++++++++++++
> >   3 files changed, 62 insertions(+)
> 
> For the series:
> 
> Acked-by: Casey Schaufler <casey@...aufler-ca.com>

Thank you!
I will wait to get some comments on the v3 and send a v4 with your tag added!

> > Best regards and thank you in advance for your reviews.
> > ---
> > [1] man capabilities
> > [2]
> > https://github.com/containerd/containerd/blob/1a078e6893d07fec10a4940a566
> > 4fab21d6f7d1e/pkg/cap/cap_linux.go#L135 [3]
> > https://github.com/moby/moby/commit/485cf38d48e7111b3d1f584d5e9eab46a902a
> > abc#diff-2e04625b209932e74c617de96682ed72fbd1bb0d0cb9fb7c709cf47a86b6f9c1
> > moby relies on containerd code.
> > [4]
> > https://github.com/syndtr/gocapability/blob/42c35b4376354fd554efc7ad35e0b
> > 7f94e3a0ffb/capability/enum.go#L47 [5]
> > https://github.com/opencontainers/runc/blob/00f56786bb220b55b41748231880b
> > a0e6380519a/libcontainer/capabilities/capabilities.go#L12 runc relies on
> > syndtr package.
> > [6]
> > https://github.com/containers/crun/blob/fafb556f09e6ffd4690c452ff51856b88
> > 0c089f1/src/libcrun/linux.c#L35