test failure in 2.19.4: dh_invalid

[thmo]

With 2.19.4, on Fedora 39, we sometimes see this test failure:

[...]
curve25519_scalar:
Curve25519 scalarmult ran 18 tests in 1.99 msec all ok
dh_invalid:
/usr/include/c++/13/bits/stl_vector.h:1125: std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](size_type) [with _Tp = unsigned char; _Alloc = Botan::secure_allocator<unsigned char>; reference = unsigned char&; size_type = long unsigned int]: Assertion '__n < this->size()' failed.

Happens sporadically on different architectures, see e.g. these (identical) build tasks: https://koji.fedoraproject.org/koji/taskinfo?taskID=115893347 and https://koji.fedoraproject.org/koji/taskinfo?taskID=115892174

Any idea what could be causing this?

[randombit]

Have you seen this occur with any prior versions?

The only change between 2.19.3 and 2.19.4 that seems even possibly related was the change in gcd from #3912

We haven't seen any similar problems on master, but possibly something went wrong with the backport.

[thmo]

Have you seen this occur with any prior versions?

Not that I am aware of. The last FTBFS was #3896 (and we have that as patch.)

Interestingly I only see the issue on F39, but maybe I was lucky.

[thmo]

FWIW, in a local rebuild (also on F39), the assertion failed at a different test:

ecdsa_verify_wycheproof:
/usr/include/c++/13/bits/stl_vector.h:1125: std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](size_type) [with _Tp = unsigned char; _Alloc = Botan::secure_allocator<unsigned char>; reference = unsigned char&; size_type = long unsigned int]: Assertion '__n < this->size()' failed.

[thmo]

If you have suggestions, I can try that. Unfortunately the issue is not reproducible reliably, and I never saw it (yet) when running a single test of the test suite.