![Jann Horn](/assets/img/avatar_default.png)
Check whether inputs from userspace are too long (explicit length field too
big or string not null-terminated) to avoid out-of-bounds reads.
As far as I can tell, this can at worst lead to very limited kernel heap
memory disclosure or oopses.
This bug can be triggered by an unprivileged user even if the xt_bpf module
is not loaded: iptables is available in network namespaces, and the xt_bpf
module can be autoloaded.
Triggering the bug with a classic BPF filter with fake length 0x1000 causes
the following KASAN report:
==================================================================
BUG: KASAN: slab-out-of-bounds in bpf_prog_create+0x84/0xf0
Read of size 32768 at addr ffff8801eff2c494 by task test/4627
CPU: 0 PID: 4627 Comm: test Not tainted 4.15.0-rc1+ #1
[...]
Call Trace:
dump_stack+0x5c/0x85
print_address_description+0x6a/0x260
kasan_report+0x254/0x370
? bpf_prog_create+0x84/0xf0
memcpy+0x1f/0x50
bpf_prog_create+0x84/0xf0
bpf_mt_check+0x90/0xd6 [xt_bpf]
[...]
Allocated by task 4627:
kasan_kmalloc+0xa0/0xd0
__kmalloc_node+0x47/0x60
xt_alloc_table_info+0x41/0x70 [x_tables]
[...]
The buggy address belongs to the object at ffff8801eff2c3c0
which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 212 bytes inside of
2048-byte region [ffff8801eff2c3c0, ffff8801eff2cbc0)
[...]
==================================================================
Fixes: e6f30c7317
("netfilter: x_tables: add xt_bpf match")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
165 lines
3.9 KiB
C
165 lines
3.9 KiB
C
/* Xtables module to match packets using a BPF filter.
|
|
* Copyright 2013 Google Inc.
|
|
* Written by Willem de Bruijn <willemb@google.com>
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License version 2 as
|
|
* published by the Free Software Foundation.
|
|
*/
|
|
|
|
#include <linux/module.h>
|
|
#include <linux/syscalls.h>
|
|
#include <linux/skbuff.h>
|
|
#include <linux/filter.h>
|
|
#include <linux/bpf.h>
|
|
|
|
#include <linux/netfilter/xt_bpf.h>
|
|
#include <linux/netfilter/x_tables.h>
|
|
|
|
MODULE_AUTHOR("Willem de Bruijn <willemb@google.com>");
|
|
MODULE_DESCRIPTION("Xtables: BPF filter match");
|
|
MODULE_LICENSE("GPL");
|
|
MODULE_ALIAS("ipt_bpf");
|
|
MODULE_ALIAS("ip6t_bpf");
|
|
|
|
static int __bpf_mt_check_bytecode(struct sock_filter *insns, __u16 len,
|
|
struct bpf_prog **ret)
|
|
{
|
|
struct sock_fprog_kern program;
|
|
|
|
if (len > XT_BPF_MAX_NUM_INSTR)
|
|
return -EINVAL;
|
|
|
|
program.len = len;
|
|
program.filter = insns;
|
|
|
|
if (bpf_prog_create(ret, &program)) {
|
|
pr_info("bpf: check failed: parse error\n");
|
|
return -EINVAL;
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
static int __bpf_mt_check_fd(int fd, struct bpf_prog **ret)
|
|
{
|
|
struct bpf_prog *prog;
|
|
|
|
prog = bpf_prog_get_type(fd, BPF_PROG_TYPE_SOCKET_FILTER);
|
|
if (IS_ERR(prog))
|
|
return PTR_ERR(prog);
|
|
|
|
*ret = prog;
|
|
return 0;
|
|
}
|
|
|
|
static int __bpf_mt_check_path(const char *path, struct bpf_prog **ret)
|
|
{
|
|
mm_segment_t oldfs = get_fs();
|
|
int retval, fd;
|
|
|
|
if (strnlen(path, XT_BPF_PATH_MAX) == XT_BPF_PATH_MAX)
|
|
return -EINVAL;
|
|
|
|
set_fs(KERNEL_DS);
|
|
fd = bpf_obj_get_user(path, 0);
|
|
set_fs(oldfs);
|
|
if (fd < 0)
|
|
return fd;
|
|
|
|
retval = __bpf_mt_check_fd(fd, ret);
|
|
sys_close(fd);
|
|
return retval;
|
|
}
|
|
|
|
static int bpf_mt_check(const struct xt_mtchk_param *par)
|
|
{
|
|
struct xt_bpf_info *info = par->matchinfo;
|
|
|
|
return __bpf_mt_check_bytecode(info->bpf_program,
|
|
info->bpf_program_num_elem,
|
|
&info->filter);
|
|
}
|
|
|
|
static int bpf_mt_check_v1(const struct xt_mtchk_param *par)
|
|
{
|
|
struct xt_bpf_info_v1 *info = par->matchinfo;
|
|
|
|
if (info->mode == XT_BPF_MODE_BYTECODE)
|
|
return __bpf_mt_check_bytecode(info->bpf_program,
|
|
info->bpf_program_num_elem,
|
|
&info->filter);
|
|
else if (info->mode == XT_BPF_MODE_FD_ELF)
|
|
return __bpf_mt_check_fd(info->fd, &info->filter);
|
|
else if (info->mode == XT_BPF_MODE_PATH_PINNED)
|
|
return __bpf_mt_check_path(info->path, &info->filter);
|
|
else
|
|
return -EINVAL;
|
|
}
|
|
|
|
static bool bpf_mt(const struct sk_buff *skb, struct xt_action_param *par)
|
|
{
|
|
const struct xt_bpf_info *info = par->matchinfo;
|
|
|
|
return BPF_PROG_RUN(info->filter, skb);
|
|
}
|
|
|
|
static bool bpf_mt_v1(const struct sk_buff *skb, struct xt_action_param *par)
|
|
{
|
|
const struct xt_bpf_info_v1 *info = par->matchinfo;
|
|
|
|
return !!bpf_prog_run_save_cb(info->filter, (struct sk_buff *) skb);
|
|
}
|
|
|
|
static void bpf_mt_destroy(const struct xt_mtdtor_param *par)
|
|
{
|
|
const struct xt_bpf_info *info = par->matchinfo;
|
|
|
|
bpf_prog_destroy(info->filter);
|
|
}
|
|
|
|
static void bpf_mt_destroy_v1(const struct xt_mtdtor_param *par)
|
|
{
|
|
const struct xt_bpf_info_v1 *info = par->matchinfo;
|
|
|
|
bpf_prog_destroy(info->filter);
|
|
}
|
|
|
|
static struct xt_match bpf_mt_reg[] __read_mostly = {
|
|
{
|
|
.name = "bpf",
|
|
.revision = 0,
|
|
.family = NFPROTO_UNSPEC,
|
|
.checkentry = bpf_mt_check,
|
|
.match = bpf_mt,
|
|
.destroy = bpf_mt_destroy,
|
|
.matchsize = sizeof(struct xt_bpf_info),
|
|
.usersize = offsetof(struct xt_bpf_info, filter),
|
|
.me = THIS_MODULE,
|
|
},
|
|
{
|
|
.name = "bpf",
|
|
.revision = 1,
|
|
.family = NFPROTO_UNSPEC,
|
|
.checkentry = bpf_mt_check_v1,
|
|
.match = bpf_mt_v1,
|
|
.destroy = bpf_mt_destroy_v1,
|
|
.matchsize = sizeof(struct xt_bpf_info_v1),
|
|
.usersize = offsetof(struct xt_bpf_info_v1, filter),
|
|
.me = THIS_MODULE,
|
|
},
|
|
};
|
|
|
|
static int __init bpf_mt_init(void)
|
|
{
|
|
return xt_register_matches(bpf_mt_reg, ARRAY_SIZE(bpf_mt_reg));
|
|
}
|
|
|
|
static void __exit bpf_mt_exit(void)
|
|
{
|
|
xt_unregister_matches(bpf_mt_reg, ARRAY_SIZE(bpf_mt_reg));
|
|
}
|
|
|
|
module_init(bpf_mt_init);
|
|
module_exit(bpf_mt_exit);
|