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Subject[patch 0/5] futex: More robustness tweaks
While looking for the minimal functional fix for the futex CVE, I
found a few things which can be done simpler and therefor make the
code more robust.


Change the ordering:

- Lookup waiters first. If waiters exist wake up the top priority
waiter with all sanity checks applied. That allows us to catch
manipulation of the user space value.

- Only if there are no waiters, do the atomic release

2) futex_lock_pi_atomic()

Its a maze of retry hoops and loops. Reduce it to simple and
userstandable states.

That requires to split out the lookup and validation functions from
lookup_pi_state(), but that turns out to be an overall win on

The overall cleanup results in less code and 488 bytes text size
reduction on x8664.


futex.c | 385 ++++++++++++++++++++++++++++------------------------------------
1 file changed, 171 insertions(+), 214 deletions(-)

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