This was relaxed in https://github.com/MariaDB/server/commit/27e6fd9a5968 where the setuid is only tried if mariadbd --user is specified.

This isn't the case with systemd service files (which set the user) https://github.com/MariaDB/server/blob/10.5/support-files/mariadb.service.in#L50 where
the CAP_IPC_LOCK capability gives the user the memlock rather than setuid.

So maybe it is safe to drop the mysqld_t setgid setuid from the policy for the common case of a user running systemd service which also works if they are using memlock.

While we are looking at the list, assuming sys_resource maps to CAP_SYS_RESOURCE that would only be raising the rlimit nofile, which is done in the systemd service.
in the server code this is capped anyway - https://github.com/MariaDB/server/blob/10.5/mysys/my_file.c#L42

sys_nice - seems to be related to a innodb setpriority(PRIO_PROCESS, tid, -20), which isn't fatal if it doesn't succeed. no other CAP_SYS_NICE are used.
Maybe we should have https://www.freedesktop.org/software/systemd/man/systemd.exec.html#LimitNICE= instead. Advice welcome.

allow mysqld_t self:shm create_shm_perms - not required in 10.5+ - shm no longer used for large pages - anon mmap is used.

rw_fifo_file_perms - one test case created a fifo - mysql-test/main/log_errchk.test, the server has some code to handle if log files externally created are fifos, but it doesn't create them itself.
galera code mentions fifo's a lot, however its an internal structure. Script https://github.com/MariaDB/server/blob/10.5/scripts/wsrep_sst_mariabackup.sh#L454 mentios fifos, however this
appears to just be using pv to rate limit.

https://github.com/MariaDB/server/pull/1553 is probably needed too.

I see https://github.com/fedora-selinux/selinux-policy/blob/rawhide/policy/modules/contrib/mysql.te#L106 probably covers https://github.com/MariaDB/server/pull/1131.




On Fri, Mar 12, 2021 at 10:14 PM Sergei Golubchik <serg@mariadb.org> wrote:
Hi, Lukas!

> I found that setuid/setgid is used inside mysqld_safe_helper
> (mariadbd-safe-helper).
> Are there any other cases when MariaDB uses these functions?

Yes, in the server. If the server is started with --memlock it does

  mlockall(MCL_CURRENT)

to prevent itself from being swapped. This needs root, and the server
uses setuid/setgid to drop root privileges after mlockall.

Regards,
Sergei
VP of MariaDB Server Engineering
and security@mariadb.org

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