[PATCH 6.1.y 0/2] bpf: backport CVE-2024-41045 and CVE-2024-42239 fixes

[Artem Dinaburg <artem@trailofbits.com>]

Hi Greg, Sasha, and bpf maintainers,

These patches are the small, ordered backport for CVE-2024-41045 and
CVE-2024-42239 on 6.1.y. The second patch depends on the first, so I kept
the upstream ordering instead of folding either change into the other.

The first patch is already present in 6.6.y. The 6.6.y backport of the
second patch is queued (6.6.158-rc1). Both patches are already present in
6.12.y, 6.18.y, and 7.2.y. Could you please queue this series for 6.1.y?

AI assistance: An LLM helped identify, adapt, and validate these backports;
I reviewed the resulting code and validation evidence.

Thanks,
Artem Dinaburg

Series:
  1. bpf: Fail bpf_timer_cancel when callback is being cancelled
  2. bpf: Defer work in bpf_timer_cancel_and_free