[PATCH 0/2] reftable/stack: stop dying on exhausted entropy pool

Hi,

this small patch series fixes the issue reported by Randall [1], where
an exhausted entropy pool can cause us to die when writing a new table
to the reftable stack. I _think_ that this is only an issue with the
OpenSSL backend of `csprng_bytes()`:

  - `arc4random_buf()` never returns an error.

  - `getrandom()` pulls from "/dev/urandom" by default.

  - `getentropy()` seems to block when there is not enough randomness
    available.

  - `GtlGenRandom()` I cannot really tell.

  - The fallback reads from "/dev/urandom", which also returns bytes in
    case the entropy pool is drained.

So OpenSSL's `RAND_bytes()` seems to be the only one that returns an
error when the entropy pool is empty. I did wonder whether we even need
to introduce the new flag in the first place, or whether we cannot just
use `RAND_pseudo_bytes()` unconditionally. But I'm a bit uneasy about it
given that OpenSSL has this doc:

    RAND_pseudo_bytes() puts num pseudo-random bytes into buf.
    Pseudo-random byte sequences generated by RAND_pseudo_bytes() will
    be unique if they are of sufficient length, but are not necessarily
    unpredictable. They can be used for non-cryptographic purposes and
    for certain purposes in cryptographic protocols, but usually not for
    key generation etc.

It might be too easy to accidentally rely on `csprng_bytes()` where it
actually requires strong cryptographic data, so I was erring on the side
of caution.

Thanks!

---
Patrick Steinhardt (2):
      wrapper: allow generating insecure random bytes
      reftable/stack: accept insecure random bytes

 builtin/gc.c                        |  2 +-
 reftable/stack.c                    |  4 ++--
 t/helper/test-csprng.c              |  2 +-
 t/unit-tests/t-reftable-readwrite.c |  6 +++---
 wrapper.c                           | 24 ++++++++++++++----------
 wrapper.h                           | 16 ++++++++++++----
 6 files changed, 33 insertions(+), 21 deletions(-)


---
base-commit: b74ff38af58464688b211140b90ec90598d340c6
change-id: 20250107-b4-pks-reftable-csprng-9ed4e8dd83c4