bpf: prevent leak of lsm program after failed attach

In the Linux kernel, the following vulnerability has been resolved:

bpf: prevent leak of lsm program after failed attach

In [0], we added the ability to bpf_prog_attach LSM programs to cgroups,

but in our validation to make sure the prog is meant to be attached to

BPF_LSM_CGROUP, we return too early if the check fails. This results in

lack of decrementing prog's refcnt (through bpf_prog_put)

leaving the LSM program alive past the point of the expected lifecycle.

This fix allows for the decrement to take place.

[0] https://lore.kernel.org/all/[email protected]/