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Date: Sun, 2 Aug 2020 19:23:36 -0700
From: Yonghong Song <yhs@...com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
CC: bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 1/2] bpf: change uapi for bpf iterator map
elements
On 8/2/20 6:25 PM, Andrii Nakryiko wrote:
> On Sat, Aug 1, 2020 at 9:22 PM Yonghong Song <yhs@...com> wrote:
>>
>> Commit a5cbe05a6673 ("bpf: Implement bpf iterator for
>> map elements") added bpf iterator support for
>> map elements. The map element bpf iterator requires
>> info to identify a particular map. In the above
>> commit, the attr->link_create.target_fd is used
>> to carry map_fd and an enum bpf_iter_link_info
>> is added to uapi to specify the target_fd actually
>> representing a map_fd:
>> enum bpf_iter_link_info {
>> BPF_ITER_LINK_UNSPEC = 0,
>> BPF_ITER_LINK_MAP_FD = 1,
>>
>> MAX_BPF_ITER_LINK_INFO,
>> };
>>
>> This is an extensible approach as we can grow
>> enumerator for pid, cgroup_id, etc. and we can
>> unionize target_fd for pid, cgroup_id, etc.
>> But in the future, there are chances that
>> more complex customization may happen, e.g.,
>> for tasks, it could be filtered based on
>> both cgroup_id and user_id.
>>
>> This patch changed the uapi to have fields
>> __aligned_u64 iter_info;
>> __u32 iter_info_len;
>> for additional iter_info for link_create.
>> The iter_info is defined as
>> union bpf_iter_link_info {
>> struct {
>> __u32 map_fd;
>> } map;
>> };
>>
>> So future extension for additional customization
>> will be easier. The bpf_iter_link_info will be
>> passed to target callback to validate and generic
>> bpf_iter framework does not need to deal it any
>> more.
>>
>> Signed-off-by: Yonghong Song <yhs@...com>
>> ---
>> include/linux/bpf.h | 10 ++++---
>> include/uapi/linux/bpf.h | 15 +++++-----
>> kernel/bpf/bpf_iter.c | 52 +++++++++++++++-------------------
>> kernel/bpf/map_iter.c | 37 ++++++++++++++++++------
>> kernel/bpf/syscall.c | 2 +-
>> net/core/bpf_sk_storage.c | 37 ++++++++++++++++++------
>> tools/include/uapi/linux/bpf.h | 15 +++++-----
>> 7 files changed, 104 insertions(+), 64 deletions(-)
>>
>
> [...]
>
>> int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
>> {
>> + union bpf_iter_link_info __user *ulinfo;
>> struct bpf_link_primer link_primer;
>> struct bpf_iter_target_info *tinfo;
>> - struct bpf_iter_aux_info aux = {};
>> + union bpf_iter_link_info linfo;
>> struct bpf_iter_link *link;
>> - u32 prog_btf_id, target_fd;
>> + u32 prog_btf_id, linfo_len;
>> bool existed = false;
>> - struct bpf_map *map;
>> int err;
>>
>> + memset(&linfo, 0, sizeof(union bpf_iter_link_info));
>> +
>> + ulinfo = u64_to_user_ptr(attr->link_create.iter_info);
>> + linfo_len = attr->link_create.iter_info_len;
>> + if (ulinfo && linfo_len) {
>
> We probably want to be more strict here: if either pointer or len is
> non-zero, both should be present and valid. Otherwise we can have
> garbage in iter_info, as long as iter_info_len is zero.
yes, it is possible iter_info_len = 0 and iter_info is not null and
if this happens, iter_info will not be examined.
in kernel, we have places this is handled similarly. For example,
for cgroup bpf_prog query.
kernel/bpf/cgroup.c, function __cgroup_bpf_query
__u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
...
if (attr->query.prog_cnt == 0 || !prog_ids || !cnt)
return 0;
In the above case, it is possible prog_cnt = 0 and prog_ids != NULL,
or prog_ids == NULL and prog_cnt != 0, and we won't return error
to user space.
Not 100% sure whether we have convention here or not.
>
>> + err = bpf_check_uarg_tail_zero(ulinfo, sizeof(linfo),
>> + linfo_len);
>> + if (err)
>> + return err;
>> + linfo_len = min_t(u32, linfo_len, sizeof(linfo));
>> + if (copy_from_user(&linfo, ulinfo, linfo_len))
>> + return -EFAULT;
>> + }
>> +
>> prog_btf_id = prog->aux->attach_btf_id;
>> mutex_lock(&targets_mutex);
>> list_for_each_entry(tinfo, &targets, list) {
>> @@ -411,13 +425,6 @@ int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
>> if (!existed)
>> return -ENOENT;
>>
>> - /* Make sure user supplied flags are target expected. */
>> - target_fd = attr->link_create.target_fd;
>> - if (attr->link_create.flags != tinfo->reg_info->req_linfo)
>> - return -EINVAL;
>> - if (!attr->link_create.flags && target_fd)
>> - return -EINVAL;
>> -
>
> Please still ensure that no flags are specified.
Make sense. I also need to ensure target_fd is 0 since it is not used
any more.
>
>
>> link = kzalloc(sizeof(*link), GFP_USER | __GFP_NOWARN);
>> if (!link)
>> return -ENOMEM;
>> @@ -431,28 +438,15 @@ int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
>> return err;
>> }
>>
>
> [...]
>
>> -static int bpf_iter_check_map(struct bpf_prog *prog,
>> - struct bpf_iter_aux_info *aux)
>> +static int bpf_iter_attach_map(struct bpf_prog *prog,
>> + union bpf_iter_link_info *linfo,
>> + struct bpf_iter_aux_info *aux)
>> {
>> - struct bpf_map *map = aux->map;
>> + struct bpf_map *map;
>> + int err = -EINVAL;
>>
>> - if (map->map_type != BPF_MAP_TYPE_SK_STORAGE)
>> + if (!linfo->map.map_fd)
>> return -EINVAL;
>
> This could be -EBADF?
Good suggestion. Will do.
>
>>
>> - if (prog->aux->max_rdonly_access > map->value_size)
>> - return -EACCES;
>> + map = bpf_map_get_with_uref(linfo->map.map_fd);
>> + if (IS_ERR(map))
>> + return PTR_ERR(map);
>> +
>> + if (map->map_type != BPF_MAP_TYPE_SK_STORAGE)
>> + goto put_map;
>> +
>> + if (prog->aux->max_rdonly_access > map->value_size) {
>> + err = -EACCES;
>> + goto put_map;
>> + }
>
> [...]
>
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