On 1/25/23 16:15, Vladislav Odintsov wrote:
> Hi,
>
> I’m a bit confused about linux unix socket files permissions, created by ovs
> daemons.
>
> From source code [0] I see it sets 0770 fchmod on file descriptor prior to
> socket bind(), assuming that sock file when creates will inherit FD’s
> permissions. So, I expect that after unix socket files created, they have
> rwxrwx--- permissions.
>
> However if running, for instance, ovsdb-server as root, it seems that this
> fchmod() call has no effect. Instead default root umask (0022) seems to be
> used:
>
> # ovsdb-server --remote punix:///var/run/openvswitch/ovs.sock
> /etc/openvswitch/ovs.db
> # ls -l /var/run/openvswitch/ovs.sock
> srwxr-x--- 1 root root 0 Jan 25 17:48 /var/run/openvswitch/ovs.sock
The requested mode and umask are both effective.
The result is (mode & ~umask). In your case:
0770 & ~0022 = 0750, i.e. rwxr-x---
>
> If switch user to non-root (default umask 0002):
>
> $ ovsdb-server --remote punix://$(pwd)/ovs.sock --unixctl=$(pwd)/ctl.sock
> ./ovs.db
> $ ls -l ovs.sock
> srwxrwx--- 1 vlodintsov vlodintsov 0 Jan 25 17:42 ovs.sock
0770 & ~0002 = 0770
>
> If running as root, passing desired user as an argument to ovsdb-server, it
> still has the same as just root behaviour:
>
> # ovsdb-server --remote punix:///var/run/openvswitch/ovs.sock
> /etc/openvswitch/ovs.db --user openvswitch:openvswitch
> # ls -l /var/run/openvswitch/ovs.sock
> srwxr-x--- 1 openvswitch openvswitch 0 Jan 25 17:47
> /var/run/openvswitch/ovs.sock
>
>
> This line of code [0] is quite old (about 8 years), so what am I doing wrong?
> Is it possible to make socket writable by group without extenal call chmod
> 0770 <path_to_socket> ?
Process has inherited umask from the current shell, i.e. the parent
process. umask is not a property of a user, it is typically set for
a shell session in bashrc or /etc/profile.
OVS has no way to know what is the desired umask for the user we're
switching to. So, it remains the same as it was.
Changing the umask for a current shell before starting the process
should help, e.g.
(umask 0002 && \
ovsdb-server --remote punix:$(pwd)/ovs.sock /etc/openvswitch/ovs.db \
--user openvswitch:openvswitch)
Best regards, Ilya Maximets.
>
> 0: https://github.com/openvswitch/ovs/blob/v2.17.5/lib/socket-util-unix.c#L264
>
> Regards,
> Vladislav Odintsov
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