Messages in this thread | | | From | Francis Laniel <> | Subject | Re: [RFC PATCH v1 0/2] Add capabilities file to sysfs | Date | Tue, 28 Dec 2021 14:34:24 +0100 |
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Hi.
Le lundi 27 décembre 2021, 23:22:41 CET Casey Schaufler a écrit : > On 12/27/2021 12:54 PM, 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/capabilities. > > This should be /sys/kernel/security/capabilities.
I began to write code to move this under /sys/kernel/security/capabilities but I realized this directory is linked to CONFIG_SECURITYFS. This option is not required to be able to run container [1]. Also, kernel/capability.c is always compiled, so I think it is better if this file (i.e. the one which prints capabilities to user) does not depend on any CONFIG_.
What do you think of it? Does this sound acceptable for you?
> > 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 underlying kernel attribute is read-only and its content is the > > capability number associated with the capability name: > > root@vm-amd64:~# cat /sys/kernel/capabilities > > 0 CAP_CHOWN > > 1 CAP_DAC_OVERRIDE > > ... > > 39 CAP_BPF > > > > 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. > > > > Francis Laniel (2): > > capability: Add cap_strings. > > kernel/ksysfs.c: Add capabilities attribute. > > > > include/uapi/linux/capability.h | 1 + > > kernel/capability.c | 45 +++++++++++++++++++++++++++++++++ > > kernel/ksysfs.c | 18 +++++++++++++ > > 3 files changed, 64 insertions(+) > > > > 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
Best regards. --- [1] https://github.com/moby/moby/blob/ 10aecb0e652d346130a37e5b4383eca28f594c21/contrib/check-config.sh
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