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selinux: convert policy read-write lock to RCU

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Convert the policy read-write lock to RCU.  This is significantly
simplified by the earlier work to encapsulate the policy data
structures and refactor the policy load and boolean setting logic.
Move the latest_granting sequence number into the selinux_policy
structure so that it can be updated atomically with the policy.
Since removing the policy rwlock and moving latest_granting reduces
the selinux_ss structure to nothing more than a wrapper around the
selinux_policy pointer, get rid of the extra layer of indirection.

At present this change merely passes a hardcoded 1 to
rcu_dereference_check() in the cases where we know we do not need to
take rcu_read_lock(), with the preceding comment explaining why.
Alternatively we could pass fsi->mutex down from selinuxfs and
apply a lockdep check on it instead.

Based in part on earlier attempts to convert the policy rwlock
to RCU by Kaigai Kohei [1] and by Peter Enderborg [2].

[1] https://lore.kernel.org/selinux/6e2f9128-e191-ebb3-0e87-74bfccb0767f@tycho.nsa.gov/
[2] https://lore.kernel.org/selinux/20180530141104.28569-1-peter.enderborg@sony.com/

Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Reviewed-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Stephen Smalley
2020-08-19 15:45:16 -04:00
committed by Paul Moore
parent c76a2f9ecd
commit 1b8b31a2e6
4 changed files with 280 additions and 218 deletions
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487
security/selinux/ss/services.c
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5
security/selinux/ss/services.h
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@@ -26,12 +26,7 @@ struct selinux_policy {
struct sidtab *sidtab;
struct policydb policydb;
struct selinux_map map;
};
struct selinux_ss {
rwlock_t policy_rwlock;
u32 latest_granting;
struct selinux_policy *policy;
} __randomize_layout;
void services_compute_xperms_drivers(struct extended_perms *xperms,