In the Linux kernel, the following vulnerability has been resolved: bpf: Require frozen map for...

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

bpf: Require frozen map for calculating map hash

Currently, bpf_map_get_info_by_fd calculates and caches the hash of the map regardless of the map's frozen state.

This leads to a TOCTOU bug where userspace can call BPF_OBJ_GET_INFO_BY_FD to cache the hash and then modify the map contents before freezing.

Therefore, a trusted loader can be tricked into verifying the stale hash while loading the modified contents.

Fix this by returning -EPERM if the map is not frozen when the hash is requested. This ensures the hash is only generated for the final, immutable state of the map.