bpf: Fix security_bpf_map_create error handling

Commit 5816bf4273ed ("lsm,selinux: Add LSM blob support for BPF objects") made the LSM hook wrappers for BPF object creation clean up the LSM state internally upon denial, e.g. security_bpf_map_create() internally calls security_bpf_map_free() when the bpf_map_create hook returns an error. map_create() however still routes a denial to its free_map_sec label, which invokes security_bpf_map_free() a second time, so the bpf_map_free hook fires twice for a single denied map. In-tree LSMs are unaffected in practice since the blob kfree() inside security_bpf_map_free() is NULL-safe and idempotent and none of them implement bpf_map_free, but a BPF LSM program attached to that hook observes double invocations. Route the denial to free_map instead.

DBDaniel Borkmann committed 4 months ago