sched_ext: bpf_iter_scx_dsq_new() should always initialize iterator

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: sched_ext: bpf_iter_scx_dsq_new() should always initialize iterator BPF programs may call next() and destroy() on BPF iterators even after new() returns an error value (e.g. bpf_for_each() macro ignores error returns from new()). bpf_iter_scx_dsq_new() could leave the iterator in an uninitialized state after an error return causing bpf_iter_scx_dsq_next() to dereference garbage data. Make bpf_iter_scx_dsq_new() always clear $kit->dsq so that next() and destroy() become noops.

References

• https://git.kernel.org/stable/c/0102989af4c334d1d98b2a0fd4d61a5152e39b72
• https://git.kernel.org/stable/c/255dd31bfc4a67a19b1fc2cd130a50284dadfe3a
• https://git.kernel.org/stable/c/428dc9fc0873989d73918d4a9cc22745b7bbc799