Hash-chain cycle in link_elf_lookup_symbol causes kernel infinite-loop DoS

Summary

link_elf_lookup_symbol (link_elf.c:812-838): while(symnum!=STN_UNDEF) follows ef->chains[symnum] (attacker-controlled module buffer); bounds check at :813 only rejects symnum>=nchains, no cycle detection; crafted 2-cycle (chains[1]=2,chains[2]=1) with bucket[0]=1 -> infinite loop pinning CPU. Reached during relocate_file for every global-symbol relocation. Root-only defense-in-depth.