Commit d1a374a1 authored by Kumar Kartikeya Dwivedi's avatar Kumar Kartikeya Dwivedi Committed by Daniel Borkmann
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bpf: Limit maximum modifier chain length in btf_check_type_tags 



On processing a module BTF of module built for an older kernel, we might
sometimes find that some type points to itself forming a loop. If such a
type is a modifier, btf_check_type_tags's while loop following modifier
chain will be caught in an infinite loop.

Fix this by defining a maximum chain length and bailing out if we spin
any longer than that.

Fixes: eb596b09 ("bpf: Ensure type tags precede modifiers in BTF")
Reported-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20220615042151.2266537-1-memxor@gmail.com
parent 3046a827

kernel/bpf/btf.c

+5 −0
Original line number Diff line number Diff line
@@ -4815,6 +4815,7 @@ static int btf_check_type_tags(struct btf_verifier_env *env, 
	n = btf_nr_types(btf);

	for (i = start_id; i < n; i++) {

		const struct btf_type *t;

		int chain_limit = 32;

		u32 cur_id = i;



		t = btf_type_by_id(btf, i);
@@ -4827,6 +4828,10 @@ static int btf_check_type_tags(struct btf_verifier_env *env, 


		in_tags = btf_type_is_type_tag(t);

		while (btf_type_is_modifier(t)) {

			if (!chain_limit--) {

				btf_verifier_log(env, "Max chain length or cycle detected");

				return -ELOOP;

			}

			if (btf_type_is_type_tag(t)) {

				if (!in_tags) {

					btf_verifier_log(env, "Type tags don't precede modifiers");