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SubjectSystem-wide hard RLIMIT_STACK in 4.14.4+ w/ SELinux
Date
Hello,

Commit 04e35f4495dd560db30c25efca4eecae8ec8c375 "exec: avoid RLIMIT_STACK
races with prlimit()" that made it into 4.14.4 effectively changes the default
hard RLIMIT_STACK on machines with SELinux (seen on Fedora 27).

selinux_bprm_set_creds() sets bprm->secureexec for any SELinux domain
transition that does not have the "noatsecure" permission. The secureexec
logic thus kicks in for virtually every process launched by PID 1 systemd
(init_t), including gettys, display managers, etc.

I can see that 8 MiB "should be enough for everyone" using normal software,
but sadly the HPC stuff around here tends to need a little more (due to a
deficiency in gfortran).

Minimal example (the actual types are not too important):

# /bin/ulimit -Hs
unlimited
# runcon -r system_r -t sysadm_t runcon -t rpm_script_t /bin/ulimit -Hs
8192

Of course this can be somewhat worked around by adjusting the SELinux policy
(allowing blanket noatsecure permission for init_t and possibly others) or by
pam_limits (for components using PAM). Unfortunately, systemd's LimitSTACK= is
also broken (calls setrlimit before exec). Anyway, I wasn't expecting any of
that in connection with the 4.14.3->.4 upgrade.

--
Best regards,

Tomáš Trnka
Software for Chemistry & Materials

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