[PATCH bpf-next v1 07/19] bpf: create anonymous bpf iterator

Yonghong Song
2020-04-27T20:13:30Z

A new bpf command BPF_ITER_CREATE is added.

The anonymous bpf iterator is seq_file based.
The seq_file private data are referenced by targets.
The bpf_iter infrastructure allocated additional space
at seq_file->private after the space used by targets
to store some meta data, e.g.,
prog: prog to run
session_id: an unique id for each opened seq_file
seq_num: how many times bpf programs are queried in this session
has_last: indicate whether or not bpf_prog has been called after
all valid objects have been processed

A map between file and prog/link is established to help
fops->release(). When fops->release() is called, just based on
inode and file, bpf program cannot be located since target
seq_priv_size not available. This map helps retrieve the prog
whose reference count needs to be decremented.

Signed-off-by: Yonghong Song <yhs@fb.com>
---
include/linux/bpf.h | 3 +
include/uapi/linux/bpf.h | 6 ++
kernel/bpf/bpf_iter.c | 162 ++++++++++++++++++++++++++++++++-
kernel/bpf/syscall.c | 27 ++++++
tools/include/uapi/linux/bpf.h | 6 ++
5 files changed, 203 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 4fc39d9b5cd0..0f0cafc65a04 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1112,6 +1112,8 @@ struct bpf_link *bpf_link_get_from_fd(u32 ufd);
int bpf_obj_pin_user(u32 ufd, const char __user *pathname);
int bpf_obj_get_user(const char __user *pathname, int flags);

+#define BPF_DUMP_SEQ_NET_PRIVATE BIT(0)
+
struct bpf_iter_reg {
const char *target;
const char *target_func_name;
@@ -1133,6 +1135,7 @@ int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx);
int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
int bpf_iter_link_replace(struct bpf_link *link, struct bpf_prog *old_prog,
struct bpf_prog *new_prog);
+int bpf_iter_new_fd(struct bpf_link *link);

int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value);
int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index f39b9fec37ab..576651110d16 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -113,6 +113,7 @@ enum bpf_cmd {
BPF_MAP_DELETE_BATCH,
BPF_LINK_CREATE,
BPF_LINK_UPDATE,
+ BPF_ITER_CREATE,
};

enum bpf_map_type {
@@ -590,6 +591,11 @@ union bpf_attr {
__u32 old_prog_fd;
} link_update;

+ struct { /* struct used by BPF_ITER_CREATE command */
+ __u32 link_fd;
+ __u32 flags;
+ } iter_create;
+
} __attribute__((aligned(8)));

/* The description below is an attempt at providing documentation to eBPF
diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index fc1ce5ee5c3f..1f4e778d1814 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -2,6 +2,7 @@
/* Copyright (c) 2020 Facebook */

#include <linux/fs.h>
+#include <linux/anon_inodes.h>
#include <linux/filter.h>
#include <linux/bpf.h>

@@ -19,6 +20,19 @@ struct bpf_iter_link {
struct bpf_iter_target_info *tinfo;
};

+struct extra_priv_data {
+ struct bpf_prog *prog;
+ u64 session_id;
+ u64 seq_num;
+ bool has_last;
+};
+
+struct anon_file_prog_assoc {
+ struct list_head list;
+ struct file *file;
+ struct bpf_prog *prog;
+};
+
static struct list_head targets;
static struct mutex targets_mutex;
static bool bpf_iter_inited = false;
@@ -26,6 +40,50 @@ static bool bpf_iter_inited = false;
/* protect bpf_iter_link.link->prog upddate */
static struct mutex bpf_iter_mutex;

+/* Since at anon seq_file release function, the prog cannot
+ * be retrieved since target seq_priv_size is not available.
+ * Keep a list of <anon_file, prog> mapping, so that
+ * at file release stage, the prog can be released properly.
+ */
+static struct list_head anon_iter_info;
+static struct mutex anon_iter_info_mutex;
+
+/* incremented on every opened seq_file */
+static atomic64_t session_id;
+
+static u32 get_total_priv_dsize(u32 old_size)
+{
+ return roundup(old_size, 8) + sizeof(struct extra_priv_data);
+}
+
+static void *get_extra_priv_dptr(void *old_ptr, u32 old_size)
+{
+ return old_ptr + roundup(old_size, 8);
+}
+
+static int anon_iter_release(struct inode *inode, struct file *file)
+{
+ struct anon_file_prog_assoc *finfo;
+
+ mutex_lock(&anon_iter_info_mutex);
+ list_for_each_entry(finfo, &anon_iter_info, list) {
+ if (finfo->file == file) {
+ bpf_prog_put(finfo->prog);
+ list_del(&finfo->list);
+ kfree(finfo);
+ break;
+ }
+ }
+ mutex_unlock(&anon_iter_info_mutex);
+
+ return seq_release_private(inode, file);
+}
+
+static const struct file_operations anon_bpf_iter_fops = {
+ .read = seq_read,
+ .release = anon_iter_release,
+};
+
int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
{
struct bpf_iter_target_info *tinfo;
@@ -37,6 +95,8 @@ int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
INIT_LIST_HEAD(&targets);
mutex_init(&targets_mutex);
mutex_init(&bpf_iter_mutex);
+ INIT_LIST_HEAD(&anon_iter_info);
+ mutex_init(&anon_iter_info_mutex);
bpf_iter_inited = true;
}

@@ -61,7 +121,20 @@ int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
struct bpf_prog *bpf_iter_get_prog(struct seq_file *seq, u32 priv_data_size,
u64 *session_id, u64 *seq_num, bool is_last)
{
- return NULL;
+ struct extra_priv_data *extra_data;
+
+ if (seq->file->f_op != &anon_bpf_iter_fops)
+ return NULL;
+
+ extra_data = get_extra_priv_dptr(seq->private, priv_data_size);
+ if (extra_data->has_last)
+ return NULL;
+
+ *session_id = extra_data->session_id;
+ *seq_num = extra_data->seq_num++;
+ extra_data->has_last = is_last;
+
+ return extra_data->prog;
}

int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx)
@@ -150,3 +223,90 @@ int bpf_iter_link_replace(struct bpf_link *link, struct bpf_prog *old_prog,
mutex_unlock(&bpf_iter_mutex);
return ret;
}
+
+static void init_seq_file(void *priv_data, struct bpf_iter_target_info *tinfo,
+ struct bpf_prog *prog)
+{
+ struct extra_priv_data *extra_data;
+
+ if (tinfo->target_feature & BPF_DUMP_SEQ_NET_PRIVATE)
+ set_seq_net_private((struct seq_net_private *)priv_data,
+ current->nsproxy->net_ns);
+
+ extra_data = get_extra_priv_dptr(priv_data, tinfo->seq_priv_size);
+ extra_data->session_id = atomic64_add_return(1, &session_id);
+ extra_data->prog = prog;
+ extra_data->seq_num = 0;
+ extra_data->has_last = false;
+}
+
+static int prepare_seq_file(struct file *file, struct bpf_iter_link *link)
+{
+ struct anon_file_prog_assoc *finfo;
+ struct bpf_iter_target_info *tinfo;
+ struct bpf_prog *prog;
+ u32 total_priv_dsize;
+ void *priv_data;
+
+ finfo = kmalloc(sizeof(*finfo), GFP_USER | __GFP_NOWARN);
+ if (!finfo)
+ return -ENOMEM;
+
+ mutex_lock(&bpf_iter_mutex);
+ prog = link->link.prog;
+ bpf_prog_inc(prog);
+ mutex_unlock(&bpf_iter_mutex);
+
+ tinfo = link->tinfo;
+ total_priv_dsize = get_total_priv_dsize(tinfo->seq_priv_size);
+ priv_data = __seq_open_private(file, tinfo->seq_ops, total_priv_dsize);
+ if (!priv_data) {
+ bpf_prog_sub(prog, 1);
+ kfree(finfo);
+ return -ENOMEM;
+ }
+
+ init_seq_file(priv_data, tinfo, prog);
+
+ finfo->file = file;
+ finfo->prog = prog;
+
+ mutex_lock(&anon_iter_info_mutex);
+ list_add(&finfo->list, &anon_iter_info);
+ mutex_unlock(&anon_iter_info_mutex);
+ return 0;
+}
+
+int bpf_iter_new_fd(struct bpf_link *link)
+{
+ struct file *file;
+ int err, fd;
+
+ if (link->ops != &bpf_iter_link_lops)
+ return -EINVAL;
+
+ fd = get_unused_fd_flags(O_CLOEXEC);
+ if (fd < 0)
+ return fd;
+
+ file = anon_inode_getfile("bpf_iter", &anon_bpf_iter_fops,
+ NULL, O_CLOEXEC);
+ if (IS_ERR(file)) {
+ err = PTR_ERR(file);
+ goto free_fd;
+ }
+
+ err = prepare_seq_file(file,
+ container_of(link, struct bpf_iter_link, link));
+ if (err)
+ goto free_file;
+
+ fd_install(fd, file);
+ return fd;
+
+free_file:
+ fput(file);
+free_fd:
+ put_unused_fd(fd);
+ return err;
+}
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index b7af4f006f2e..458f7000887a 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3696,6 +3696,30 @@ static int link_update(union bpf_attr *attr)
return ret;
}

+#define BPF_ITER_CREATE_LAST_FIELD iter_create.flags
+
+static int bpf_iter_create(union bpf_attr *attr)
+{
+ struct bpf_link *link;
+ int err;
+
+ if (CHECK_ATTR(BPF_ITER_CREATE))
+ return -EINVAL;
+
+ if (attr->iter_create.flags)
+ return -EINVAL;
+
+ link = bpf_link_get_from_fd(attr->iter_create.link_fd);
+ if (IS_ERR(link))
+ return PTR_ERR(link);
+
+ err = bpf_iter_new_fd(link);
+ if (err < 0)
+ bpf_link_put(link);
+
+ return err;
+}
+
SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
{
union bpf_attr attr;
@@ -3813,6 +3837,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
case BPF_LINK_UPDATE:
err = link_update(&attr);
break;
+ case BPF_ITER_CREATE:
+ err = bpf_iter_create(&attr);
+ break;
default:
err = -EINVAL;
break;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index f39b9fec37ab..576651110d16 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -113,6 +113,7 @@ enum bpf_cmd {
BPF_MAP_DELETE_BATCH,
BPF_LINK_CREATE,
BPF_LINK_UPDATE,
+ BPF_ITER_CREATE,
};

enum bpf_map_type {
@@ -590,6 +591,11 @@ union bpf_attr {
__u32 old_prog_fd;
} link_update;

+ struct { /* struct used by BPF_ITER_CREATE command */
+ __u32 link_fd;
+ __u32 flags;
+ } iter_create;
+
} __attribute__((aligned(8)));

/* The description below is an attempt at providing documentation to eBPF
--
2.24.1