Affected: Linux

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

bpf: copy_verifier_state() should copy 'loop_entry' field

The bpf_verifier_state.loop_entry state should be copied by copy_verifier_state(). Otherwise, .loop_entry values from unrelated states would poison env->cur_state.

Additionally, env->stack should not contain any states with .loop_entry != NULL. The states in env->stack are yet to be verified, while .loop_entry is set for states that reached an equivalent state. This means that env->cur_state->loop_entry should always be NULL after pop_stack().

See the selftest in the next commit for an example of the program that is not safe yet is accepted by verifier w/o this fix.

This change has some verification performance impact for selftests:

File Program Insns (A) Insns (B) Insns (DIFF) States (A) States (B) States (DIFF) ---------------------------------- ---------------------------- --------- --------- -------------- ---------- ---------- ------------- arena_htab.bpf.o arena_htab_llvm 717 426 -291 (-40.59%) 57 37 -20 (-35.09%) arena_htab_asm.bpf.o arena_htab_asm 597 445 -152 (-25.46%) 47 37 -10 (-21.28%) arena_list.bpf.o arena_list_del 309 279 -30 (-9.71%) 23 14 -9 (-39.13%) iters.bpf.o…