Commit e4414b01 authored by Jiri Olsa's avatar Jiri Olsa Committed by Daniel Borkmann
Browse files

bpf: Check the helper function is valid in get_helper_proto 

kernel test robot reported verifier bug [1] where the helper func
pointer could be NULL due to disabled config option.

As Alexei suggested we could check on that in get_helper_proto
directly. Marking tail_call helper func with BPF_PTR_POISON,
because it is unused by design.

  [1] https://lore.kernel.org/oe-lkp/202507160818.68358831-lkp@intel.com



Reported-by: default avatarkernel test robot <oliver.sang@intel.com>
Reported-by: default avatar <syzbot+a9ed3d9132939852d0df@syzkaller.appspotmail.com>
Suggested-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarPaul Chaignon <paul.chaignon@gmail.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20250814200655.945632-1-jolsa@kernel.org
Closes: https://lore.kernel.org/oe-lkp/202507160818.68358831-lkp@intel.com
parent 2b986b9e

kernel/bpf/core.c

+4 −1
Original line number Diff line number Diff line
@@ -3024,7 +3024,10 @@ EXPORT_SYMBOL_GPL(bpf_event_output); 


/* Always built-in helper functions. */

const struct bpf_func_proto bpf_tail_call_proto = {

	.func		= NULL,

	/* func is unused for tail_call, we set it to pass the

	 * get_helper_proto check

	 */

	.func		= BPF_PTR_POISON,

	.gpl_only	= false,

	.ret_type	= RET_VOID,

	.arg1_type	= ARG_PTR_TO_CTX,

kernel/bpf/verifier.c

+1 −1
Original line number Diff line number Diff line
@@ -11354,7 +11354,7 @@ static int get_helper_proto(struct bpf_verifier_env *env, int func_id, 
		return -EINVAL;









	*ptr = env->ops->get_func_proto(func_id, env->prog);









	return *ptr ? 0 : -EINVAL;









	return *ptr && (*ptr)->func ? 0 : -EINVAL;









}

















static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,