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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: eb596b0905 ("bpf: Ensure type tags precede modifiers in BTF")
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20220615042151.2266537-1-memxor@gmail.com
This commit is contained in:
Kumar Kartikeya Dwivedi 2022-06-15 09:51:51 +05:30 committed by Daniel Borkmann
parent 3046a82731
commit d1a374a1ae
1 changed files with 5 additions and 0 deletions
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5
kernel/bpf/btf.c
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@ -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");