tree 3f16cb7859ad7367d2459ae9abf553f9a55c4772
parent b634987fedd4f92bebb0588387c3269c7a5e5f67
author Willy Tarreau <w@1wt.eu> 1670518079 +0100
committer Willy Tarreau <w@1wt.eu> 1670522099 +0100
encoding latin1

MINOR: pools: make DEBUG_UAF a runtime setting

Since the massive pools cleanup that happened in 2.6, the pools
architecture was made quite more hierarchical and many alternate code
blocks could be moved to runtime flags set by -dM. One of them had not
been converted by then, DEBUG_UAF. It's not much more difficult actually,
since it only acts on a pair of functions indirection on the slow path
(OS-level allocator) and a default setting for the cache activation.

This patch adds the "uaf" setting to the options permitted in -dM so
that it now becomes possible to set or unset UAF at boot time without
recompiling. This is particularly convenient, because every 3 months on
average, developers ask a user to recompile haproxy with DEBUG_UAF to
understand a bug. Now it will not be needed anymore, instead the user
will only have to disable pools and enable uaf using -dMuaf. Note that
-dMuaf only disables previously enabled pools, but it remains possible
to re-enable caching by specifying the cache after, like -dMuaf,cache.
A few tests with this mode show that it can be an interesting combination
which catches significantly less UAF but will do so with much less
overhead, so it might be compatible with some high-traffic deployments.

The change is very small and isolated. It could be helpful to backport
this at least to 2.7 once confirmed not to cause build issues on exotic
systems, and even to 2.6 a bit later as this has proven to be useful
over time, and could be even more if it did not require a rebuild. If
a backport is desired, the following patches are needed as well:

  CLEANUP: pools: move the write before free to the uaf-only function
  CLEANUP: pool: only include pool-os from pool.c not pool.h
  REORG: pool: move all the OS specific code to pool-os.h
  CLEANUP: pools: get rid of CONFIG_HAP_POOLS
  DEBUG: pool: show a few examples in -dMhelp