New: Self-contradictory description of inheritable capability set

https://bugzilla.kernel.org/show_bug.cgi?id=216667

Bug ID: 216667
Summary: Self-contradictory description of inheritable
capability set
Product: Documentation
Version: unspecified
Hardware: All
OS: Linux
Status: NEW
Severity: normal
Priority: P1
Component: man-pages
Assignee: [email protected]
Reporter: [email protected]
Regression: No

man capabilities says about the inheritable capset of a process:

I understand this to mean that any capability in the inheritable set will stay inheritable across an execve (i.e. the inheritable set will not shrink across execve).

The same manpage says in the next paragraph:

This seems to say the exact opposite of how I read the previous paragraph.

I am probably misunderstanding something basic here, but I am unlikely to be the only person who does so, so I think it bears making this part clearer.

(When I try to look at the rest of the manpage to get more clarity, I fail:
- the section that describes capability transformations across execve() seems
to say that inheritable capset stays constant,
- the description of ambient capabilities implies that inheritable
capabilities differ from ambient insofar ambient ones are more "durable" across execve().)

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Monthero Ronald ([email protected]) changed:

What |Removed |Added
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CC| |[email protected]

--- Comment #1 from Monthero Ronald ([email protected]) ---

It's to make a distinction between a root user and non root user for the process. The first part of the paragraph below is for root user and the later part is for execve run as non root user. And on other hand applications ( using execve) that run with few elevated capability flags can use ambient capabilities. The statement you quoted from man page - Inheritable section below:
---
Inheritable
This is a set of capabilities preserved across an execve(2).
Inheritable capabilities remain inheritable when executing
any program, and inheritable capabilities are added to the
permitted set when executing a program that has the correspond‐
ing bits set in the file inheritable set.

Because inheritable capabilities are not generally preserved
across execve(2) when running as a non-root user, applications
that wish to run helper programs with elevated capabilities
should consider using ambient capabilities, described below.
---

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--- Comment #2 from Monthero Ronald ([email protected]) --- If curious you can also check the process capabilities set and decode their capabilities set flags for - permitted, inherited and ambient as below. The capabilities set can differ based on process , user and privileges

Example:

test$ ps alx | grep docker
4 0 2068 1 20 0 1834532 76808 - Ssl ? 0:16
/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
0 1000 70187 65976 20 0 17868 2504 pipe_r S+ pts/7 0:00 grep
--color=auto docker
test$
test$ egrep Cap /proc/2068/status
CapInh: 0000000000000000
CapPrm: 000001ffffffffff
CapEff: 000001ffffffffff
CapBnd: 000001ffffffffff
CapAmb: 0000000000000000
test$

Decode the capability flags for this process

test$ capsh --decode=000001ffffffffff 0x000001ffffffffff=cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_linux_immutable,cap_net_bind_service,cap_net_broadcast,cap_net_admin,cap_net_raw,cap_ipc_lock,cap_ipc_owner,cap_sys_module,cap_sys_rawio,cap_sys_chroot,cap_sys_ptrace,cap_sys_pacct,cap_sys_admin,cap_sys_boot,cap_sys_nice,cap_sys_resource,cap_sys_time,cap_sys_tty_config,cap_mknod,cap_lease,cap_audit_write,cap_audit_control,cap_setfcap,cap_mac_override,cap_mac_admin,cap_syslog,cap_wake_alarm,cap_block_suspend,cap_audit_read,cap_perfmon,cap_bpf,cap_checkpoint_restore test$

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--- Comment #3 from Alejandro Colomar ([email protected]) ---
If you still feel some wording could be improved, I encourage you to send a patch, according to the ./CONTRIBUTING file in the repo.

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Alejandro Colomar ([email protected]) changed:

What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |NEEDINFO

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--- Comment #4 from Monthero Ronald ([email protected]) --- imho the current info of capabilities seem congruous.

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