Re: [PATCH bpf-next v2 2/4] bpf: Limit the number of kprobes when attaching program to multiple kprobes

[Hou Tao <houtao@huaweicloud.com>]

Hi,

On 12/14/2023 7:32 AM, Andrii Nakryiko wrote:
> On Wed, Dec 13, 2023 at 3:24 AM Hou Tao <houtao@huaweicloud.com> wrote:
>> From: Hou Tao <houtao1@huawei.com>
>>
>> An abnormally big cnt may also be assigned to kprobe_multi.cnt when
>> attaching multiple kprobes. It will trigger the following warning in
>> kvmalloc_node():
>>
>>         if (unlikely(size > INT_MAX)) {
>>             WARN_ON_ONCE(!(flags & __GFP_NOWARN));
>>             return NULL;
>>         }
>>
>> Fix the warning by limiting the maximal number of kprobes in
>> bpf_kprobe_multi_link_attach().
>>
>> Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
>> Signed-off-by: Hou Tao <houtao1@huawei.com>
>> ---
>>  kernel/trace/bpf_trace.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
>> index 2d1201f7b554..944678529f5c 100644
>> --- a/kernel/trace/bpf_trace.c
>> +++ b/kernel/trace/bpf_trace.c
>> @@ -43,6 +43,7 @@
>>         rcu_dereference_protected(p, lockdep_is_held(&bpf_event_mutex))
>>
>>  #define MAX_UPROBE_MULTI_CNT (1U << 20)
>> +#define MAX_KPROBE_MULTI_CNT (1U << 20)
>>
>>  #ifdef CONFIG_MODULES
>>  struct bpf_trace_module {
>> @@ -2970,7 +2971,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>>                 return -EINVAL;
>>
>>         cnt = attr->link_create.kprobe_multi.cnt;
>> -       if (!cnt)
>> +       if (!cnt || cnt > MAX_KPROBE_MULTI_CNT)
>>                 return -EINVAL;
> let's return -E2BIG for `cnt > MAX` cases? Same in another patch

Good point. Will do in v3.
>>         size = cnt * sizeof(*addrs);
>> --
>> 2.29.2
>>