As discussed with Linus and Andy, we need to reset the stack rlimit
before we do memory layouts when execing a privilege-gaining (e.g.
setuid) program. To do this, we need to know the results of the
bprm_secureexec hook before memory layouts. As it turns out, this
can be made _mostly_ trivial by collapsing bprm_secureexec into
bprm_set_creds.
The LSMs using bprm_secureexec nearly always save state between
bprm_set_creds and bprm_secureexec. In the face of multiple calls to
bprm_set_creds (via prepare_binprm() calls from binfmt_script, etc),
all LSMs except commoncap only pay attention to the first call, so
that aligns well with collapsing bprm_secureexec into bprm_set_creds.
The commoncaps, though, needs to check the _last_ bprm_set_creds, so
this series just swaps one bprm flag for another (cap_effective is no
longer needed to save state between bprm_set_creds and bprm_secureexec,
but we do need to keep a separate state, so we add the cap_elevated flag).
Once secureexec is available to setup_new_exec() before the memory
layout, we can add an rlimit sanity-check for setuid execs. (With no
need to clean up since we're past the point of no return.)
Along the way, this fixes comments, renames a variable, and consolidates
dumpability and pdeath_signal clearing, which includes some commit log
archeology to examine the subtle differences between what we had and
what we need.
Several folks have looked at this already (thank you!) but I'd appreciate
any other eyes on this to make sure it isn't broken in some special
way. Looking at the diffstat, even after all my long comments, this is
a net reduction in lines. :)
Given this crosses a bunch of areas, I think this is likely best to go
via the -mm tree, which is where nearly all of my prior exec work has
lived too. It's also after rc2 at this point, so I'd be slightly nervous
to see this land directly in Linus's tree, but I leave that decision up
to Linus. :) Regardless, very little has changed between v3 and v4, so I
think this is ready to go.
Thanks!
-Kees
----------------------------------------------------------------
Kees Cook (15):
exec: Rename bprm->cred_prepared to called_set_creds
exec: Correct comments about "point of no return"
binfmt: Introduce secureexec flag
apparmor: Refactor to remove bprm_secureexec hook
selinux: Refactor to remove bprm_secureexec hook
smack: Refactor to remove bprm_secureexec hook
commoncap: Refactor to remove bprm_secureexec hook
commoncap: Move cap_elevated calculation into bprm_set_creds
LSM: drop bprm_secureexec hook
exec: Use secureexec for setting dumpability
exec: Use secureexec for clearing pdeath_signal
smack: Remove redundant pdeath_signal clearing
exec: Consolidate dumpability logic
exec: Use sane stack rlimit under secureexec
exec: Consolidate pdeath_signal clearing
fs/binfmt_elf.c | 2 +-
fs/binfmt_elf_fdpic.c | 2 +-
fs/binfmt_flat.c | 2 +-
fs/exec.c | 56 ++++++++++++++++++++++++++++----------
include/linux/binfmts.h | 24 ++++++++++++----
include/linux/lsm_hooks.h | 14 ++++------
include/linux/security.h | 7 -----
security/apparmor/domain.c | 24 ++--------------
security/apparmor/include/domain.h | 1 -
security/apparmor/include/file.h | 3 --
security/apparmor/lsm.c | 1 -
security/commoncap.c | 50 ++++++++--------------------------
security/security.c | 5 ----
security/selinux/hooks.c | 26 ++++--------------
security/smack/smack_lsm.c | 34 ++---------------------
security/tomoyo/tomoyo.c | 2 +-
16 files changed, 91 insertions(+), 162 deletions(-)
v4:
- add {Ack,Review,Test}ed-bys
- reorder patches to move trivial refactoring to the front
- move secureexec flag set earlier in the series to setup_new_exec(); amluto
v3:
- collapse brpm_secureexec into bprm_set_creds; ebiederm.
- continue to improve various comments
v2:
- fix missed current_security() uses in LSMs.
- research/consolidate dumpability setting logic
- research/consolidate pdeath_signal clearing logic
- split up logical steps a little more for easier review (and bisection)
- fix some old broken comments
