On 8/2/20 10:11 PM, Andrii Nakryiko wrote:
On Sun, Aug 2, 2020 at 7:23 PM Yonghong Song <yhs@xxxxxx> wrote:
On 8/2/20 6:25 PM, Andrii Nakryiko wrote:
On Sat, Aug 1, 2020 at 9:22 PM Yonghong Song <yhs@xxxxxx> 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@xxxxxx>
---
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.
I don't know either, but I'd assume that we didn't think about 100%
strictness when originally implementing this. So I'd go with a very
strict check for this new functionality.
Agreed. This should be fine as the functionality is new.
+ 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.
yep, good catch
link = kzalloc(sizeof(*link), GFP_USER | __GFP_NOWARN);
if (!link)
return -ENOMEM;
[...]
