In the Linux kernel, the following vulnerability has been resolved: bpf: Preserve unique-field state across nested structs btf_find_struct

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

bpf: Preserve unique-field state across nested structs

btf_find_struct_field() initializes a fresh seen mask for every recursive
descent. Unique special fields in different levels of the same aggregate
therefore do not see one another. The duplicate fields can reach
btf_parse_fields(), where they trigger an invariant WARN_ON_ONCE(). A
crafted user BTF can consequently trigger the warning before map creation
checks capabilities.

Initialize the seen mask once in btf_find_field() and pass the same pointer
through struct, datasec, and nested-struct walks. This gives the entire field
traversal one shared uniqueness state.