![Alexei Starovoitov](/assets/img/avatar_default.png)
Normally the program attachment place (like sockets, qdiscs) takes
care of rcu protection and calls bpf_prog_put() after a grace period.
The programs stored inside prog_array may not be attached anywhere,
so prog_array needs to take care of preserving rcu protection.
Otherwise bpf_tail_call() will race with bpf_prog_put().
To solve that introduce bpf_prog_put_rcu() helper function and use
it in 3 places where unattached program can decrement refcnt:
closing program fd, deleting/replacing program in prog_array.
Fixes: 04fd61ab36
("bpf: allow bpf programs to tail-call other bpf programs")
Reported-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
258 lines
6.5 KiB
C
258 lines
6.5 KiB
C
/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of version 2 of the GNU General Public
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* License as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*/
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#include <linux/bpf.h>
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#include <linux/err.h>
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#include <linux/vmalloc.h>
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#include <linux/slab.h>
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#include <linux/mm.h>
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#include <linux/filter.h>
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/* Called from syscall */
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static struct bpf_map *array_map_alloc(union bpf_attr *attr)
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{
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struct bpf_array *array;
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u32 elem_size, array_size;
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/* check sanity of attributes */
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if (attr->max_entries == 0 || attr->key_size != 4 ||
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attr->value_size == 0)
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return ERR_PTR(-EINVAL);
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elem_size = round_up(attr->value_size, 8);
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/* check round_up into zero and u32 overflow */
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if (elem_size == 0 ||
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attr->max_entries > (U32_MAX - sizeof(*array)) / elem_size)
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return ERR_PTR(-ENOMEM);
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array_size = sizeof(*array) + attr->max_entries * elem_size;
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/* allocate all map elements and zero-initialize them */
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array = kzalloc(array_size, GFP_USER | __GFP_NOWARN);
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if (!array) {
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array = vzalloc(array_size);
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if (!array)
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return ERR_PTR(-ENOMEM);
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}
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/* copy mandatory map attributes */
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array->map.key_size = attr->key_size;
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array->map.value_size = attr->value_size;
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array->map.max_entries = attr->max_entries;
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array->elem_size = elem_size;
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return &array->map;
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}
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/* Called from syscall or from eBPF program */
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static void *array_map_lookup_elem(struct bpf_map *map, void *key)
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{
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struct bpf_array *array = container_of(map, struct bpf_array, map);
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u32 index = *(u32 *)key;
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if (index >= array->map.max_entries)
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return NULL;
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return array->value + array->elem_size * index;
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}
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/* Called from syscall */
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static int array_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
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{
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struct bpf_array *array = container_of(map, struct bpf_array, map);
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u32 index = *(u32 *)key;
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u32 *next = (u32 *)next_key;
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if (index >= array->map.max_entries) {
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*next = 0;
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return 0;
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}
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if (index == array->map.max_entries - 1)
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return -ENOENT;
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*next = index + 1;
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return 0;
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}
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/* Called from syscall or from eBPF program */
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static int array_map_update_elem(struct bpf_map *map, void *key, void *value,
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u64 map_flags)
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{
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struct bpf_array *array = container_of(map, struct bpf_array, map);
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u32 index = *(u32 *)key;
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if (map_flags > BPF_EXIST)
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/* unknown flags */
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return -EINVAL;
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if (index >= array->map.max_entries)
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/* all elements were pre-allocated, cannot insert a new one */
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return -E2BIG;
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if (map_flags == BPF_NOEXIST)
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/* all elements already exist */
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return -EEXIST;
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memcpy(array->value + array->elem_size * index, value, array->elem_size);
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return 0;
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}
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/* Called from syscall or from eBPF program */
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static int array_map_delete_elem(struct bpf_map *map, void *key)
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{
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return -EINVAL;
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}
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/* Called when map->refcnt goes to zero, either from workqueue or from syscall */
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static void array_map_free(struct bpf_map *map)
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{
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struct bpf_array *array = container_of(map, struct bpf_array, map);
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/* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
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* so the programs (can be more than one that used this map) were
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* disconnected from events. Wait for outstanding programs to complete
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* and free the array
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*/
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synchronize_rcu();
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kvfree(array);
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}
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static const struct bpf_map_ops array_ops = {
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.map_alloc = array_map_alloc,
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.map_free = array_map_free,
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.map_get_next_key = array_map_get_next_key,
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.map_lookup_elem = array_map_lookup_elem,
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.map_update_elem = array_map_update_elem,
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.map_delete_elem = array_map_delete_elem,
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};
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static struct bpf_map_type_list array_type __read_mostly = {
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.ops = &array_ops,
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.type = BPF_MAP_TYPE_ARRAY,
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};
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static int __init register_array_map(void)
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{
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bpf_register_map_type(&array_type);
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return 0;
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}
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late_initcall(register_array_map);
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static struct bpf_map *prog_array_map_alloc(union bpf_attr *attr)
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{
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/* only bpf_prog file descriptors can be stored in prog_array map */
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if (attr->value_size != sizeof(u32))
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return ERR_PTR(-EINVAL);
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return array_map_alloc(attr);
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}
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static void prog_array_map_free(struct bpf_map *map)
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{
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struct bpf_array *array = container_of(map, struct bpf_array, map);
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int i;
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synchronize_rcu();
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/* make sure it's empty */
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for (i = 0; i < array->map.max_entries; i++)
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BUG_ON(array->prog[i] != NULL);
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kvfree(array);
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}
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static void *prog_array_map_lookup_elem(struct bpf_map *map, void *key)
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{
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return NULL;
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}
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/* only called from syscall */
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static int prog_array_map_update_elem(struct bpf_map *map, void *key,
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void *value, u64 map_flags)
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{
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struct bpf_array *array = container_of(map, struct bpf_array, map);
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struct bpf_prog *prog, *old_prog;
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u32 index = *(u32 *)key, ufd;
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if (map_flags != BPF_ANY)
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return -EINVAL;
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if (index >= array->map.max_entries)
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return -E2BIG;
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ufd = *(u32 *)value;
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prog = bpf_prog_get(ufd);
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if (IS_ERR(prog))
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return PTR_ERR(prog);
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if (!bpf_prog_array_compatible(array, prog)) {
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bpf_prog_put(prog);
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return -EINVAL;
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}
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old_prog = xchg(array->prog + index, prog);
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if (old_prog)
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bpf_prog_put_rcu(old_prog);
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return 0;
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}
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static int prog_array_map_delete_elem(struct bpf_map *map, void *key)
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{
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struct bpf_array *array = container_of(map, struct bpf_array, map);
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struct bpf_prog *old_prog;
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u32 index = *(u32 *)key;
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if (index >= array->map.max_entries)
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return -E2BIG;
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old_prog = xchg(array->prog + index, NULL);
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if (old_prog) {
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bpf_prog_put_rcu(old_prog);
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return 0;
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} else {
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return -ENOENT;
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}
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}
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/* decrement refcnt of all bpf_progs that are stored in this map */
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void bpf_prog_array_map_clear(struct bpf_map *map)
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{
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struct bpf_array *array = container_of(map, struct bpf_array, map);
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int i;
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for (i = 0; i < array->map.max_entries; i++)
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prog_array_map_delete_elem(map, &i);
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}
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static const struct bpf_map_ops prog_array_ops = {
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.map_alloc = prog_array_map_alloc,
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.map_free = prog_array_map_free,
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.map_get_next_key = array_map_get_next_key,
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.map_lookup_elem = prog_array_map_lookup_elem,
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.map_update_elem = prog_array_map_update_elem,
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.map_delete_elem = prog_array_map_delete_elem,
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};
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static struct bpf_map_type_list prog_array_type __read_mostly = {
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.ops = &prog_array_ops,
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.type = BPF_MAP_TYPE_PROG_ARRAY,
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};
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static int __init register_prog_array_map(void)
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{
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bpf_register_map_type(&prog_array_type);
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return 0;
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}
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late_initcall(register_prog_array_map);
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