linux/kernel/bpf/arraymap.c
Alexei Starovoitov abf2e7d6e2 bpf: add missing rcu protection when releasing programs from prog_array
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>
2015-05-31 00:27:51 -07:00

258 lines
6.5 KiB
C

/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of version 2 of the GNU General Public
* License as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*/
#include <linux/bpf.h>
#include <linux/err.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/filter.h>
/* Called from syscall */
static struct bpf_map *array_map_alloc(union bpf_attr *attr)
{
struct bpf_array *array;
u32 elem_size, array_size;
/* check sanity of attributes */
if (attr->max_entries == 0 || attr->key_size != 4 ||
attr->value_size == 0)
return ERR_PTR(-EINVAL);
elem_size = round_up(attr->value_size, 8);
/* check round_up into zero and u32 overflow */
if (elem_size == 0 ||
attr->max_entries > (U32_MAX - sizeof(*array)) / elem_size)
return ERR_PTR(-ENOMEM);
array_size = sizeof(*array) + attr->max_entries * elem_size;
/* allocate all map elements and zero-initialize them */
array = kzalloc(array_size, GFP_USER | __GFP_NOWARN);
if (!array) {
array = vzalloc(array_size);
if (!array)
return ERR_PTR(-ENOMEM);
}
/* copy mandatory map attributes */
array->map.key_size = attr->key_size;
array->map.value_size = attr->value_size;
array->map.max_entries = attr->max_entries;
array->elem_size = elem_size;
return &array->map;
}
/* Called from syscall or from eBPF program */
static void *array_map_lookup_elem(struct bpf_map *map, void *key)
{
struct bpf_array *array = container_of(map, struct bpf_array, map);
u32 index = *(u32 *)key;
if (index >= array->map.max_entries)
return NULL;
return array->value + array->elem_size * index;
}
/* Called from syscall */
static int array_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
{
struct bpf_array *array = container_of(map, struct bpf_array, map);
u32 index = *(u32 *)key;
u32 *next = (u32 *)next_key;
if (index >= array->map.max_entries) {
*next = 0;
return 0;
}
if (index == array->map.max_entries - 1)
return -ENOENT;
*next = index + 1;
return 0;
}
/* Called from syscall or from eBPF program */
static int array_map_update_elem(struct bpf_map *map, void *key, void *value,
u64 map_flags)
{
struct bpf_array *array = container_of(map, struct bpf_array, map);
u32 index = *(u32 *)key;
if (map_flags > BPF_EXIST)
/* unknown flags */
return -EINVAL;
if (index >= array->map.max_entries)
/* all elements were pre-allocated, cannot insert a new one */
return -E2BIG;
if (map_flags == BPF_NOEXIST)
/* all elements already exist */
return -EEXIST;
memcpy(array->value + array->elem_size * index, value, array->elem_size);
return 0;
}
/* Called from syscall or from eBPF program */
static int array_map_delete_elem(struct bpf_map *map, void *key)
{
return -EINVAL;
}
/* Called when map->refcnt goes to zero, either from workqueue or from syscall */
static void array_map_free(struct bpf_map *map)
{
struct bpf_array *array = container_of(map, struct bpf_array, map);
/* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
* so the programs (can be more than one that used this map) were
* disconnected from events. Wait for outstanding programs to complete
* and free the array
*/
synchronize_rcu();
kvfree(array);
}
static const struct bpf_map_ops array_ops = {
.map_alloc = array_map_alloc,
.map_free = array_map_free,
.map_get_next_key = array_map_get_next_key,
.map_lookup_elem = array_map_lookup_elem,
.map_update_elem = array_map_update_elem,
.map_delete_elem = array_map_delete_elem,
};
static struct bpf_map_type_list array_type __read_mostly = {
.ops = &array_ops,
.type = BPF_MAP_TYPE_ARRAY,
};
static int __init register_array_map(void)
{
bpf_register_map_type(&array_type);
return 0;
}
late_initcall(register_array_map);
static struct bpf_map *prog_array_map_alloc(union bpf_attr *attr)
{
/* only bpf_prog file descriptors can be stored in prog_array map */
if (attr->value_size != sizeof(u32))
return ERR_PTR(-EINVAL);
return array_map_alloc(attr);
}
static void prog_array_map_free(struct bpf_map *map)
{
struct bpf_array *array = container_of(map, struct bpf_array, map);
int i;
synchronize_rcu();
/* make sure it's empty */
for (i = 0; i < array->map.max_entries; i++)
BUG_ON(array->prog[i] != NULL);
kvfree(array);
}
static void *prog_array_map_lookup_elem(struct bpf_map *map, void *key)
{
return NULL;
}
/* only called from syscall */
static int prog_array_map_update_elem(struct bpf_map *map, void *key,
void *value, u64 map_flags)
{
struct bpf_array *array = container_of(map, struct bpf_array, map);
struct bpf_prog *prog, *old_prog;
u32 index = *(u32 *)key, ufd;
if (map_flags != BPF_ANY)
return -EINVAL;
if (index >= array->map.max_entries)
return -E2BIG;
ufd = *(u32 *)value;
prog = bpf_prog_get(ufd);
if (IS_ERR(prog))
return PTR_ERR(prog);
if (!bpf_prog_array_compatible(array, prog)) {
bpf_prog_put(prog);
return -EINVAL;
}
old_prog = xchg(array->prog + index, prog);
if (old_prog)
bpf_prog_put_rcu(old_prog);
return 0;
}
static int prog_array_map_delete_elem(struct bpf_map *map, void *key)
{
struct bpf_array *array = container_of(map, struct bpf_array, map);
struct bpf_prog *old_prog;
u32 index = *(u32 *)key;
if (index >= array->map.max_entries)
return -E2BIG;
old_prog = xchg(array->prog + index, NULL);
if (old_prog) {
bpf_prog_put_rcu(old_prog);
return 0;
} else {
return -ENOENT;
}
}
/* decrement refcnt of all bpf_progs that are stored in this map */
void bpf_prog_array_map_clear(struct bpf_map *map)
{
struct bpf_array *array = container_of(map, struct bpf_array, map);
int i;
for (i = 0; i < array->map.max_entries; i++)
prog_array_map_delete_elem(map, &i);
}
static const struct bpf_map_ops prog_array_ops = {
.map_alloc = prog_array_map_alloc,
.map_free = prog_array_map_free,
.map_get_next_key = array_map_get_next_key,
.map_lookup_elem = prog_array_map_lookup_elem,
.map_update_elem = prog_array_map_update_elem,
.map_delete_elem = prog_array_map_delete_elem,
};
static struct bpf_map_type_list prog_array_type __read_mostly = {
.ops = &prog_array_ops,
.type = BPF_MAP_TYPE_PROG_ARRAY,
};
static int __init register_prog_array_map(void)
{
bpf_register_map_type(&prog_array_type);
return 0;
}
late_initcall(register_prog_array_map);