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kernel-ark/include/linux/netfilter.h
Neil Horman 16fcec35e7 [NETFILTER]: Fix/improve deadlock condition on module removal netfilter 
So I've had a deadlock reported to me.  I've found that the sequence of
events goes like this:

1) process A (modprobe) runs to remove ip_tables.ko

2) process B (iptables-restore) runs and calls setsockopt on a netfilter socket,
increasing the ip_tables socket_ops use count

3) process A acquires a file lock on the file ip_tables.ko, calls remove_module
in the kernel, which in turn executes the ip_tables module cleanup routine,
which calls nf_unregister_sockopt

4) nf_unregister_sockopt, seeing that the use count is non-zero, puts the
calling process into uninterruptible sleep, expecting the process using the
socket option code to wake it up when it exits the kernel

4) the user of the socket option code (process B) in do_ipt_get_ctl, calls
ipt_find_table_lock, which in this case calls request_module to load
ip_tables_nat.ko

5) request_module forks a copy of modprobe (process C) to load the module and
blocks until modprobe exits.

6) Process C. forked by request_module process the dependencies of
ip_tables_nat.ko, of which ip_tables.ko is one.

7) Process C attempts to lock the request module and all its dependencies, it
blocks when it attempts to lock ip_tables.ko (which was previously locked in
step 3)

Theres not really any great permanent solution to this that I can see, but I've
developed a two part solution that corrects the problem

Part 1) Modifies the nf_sockopt registration code so that, instead of using a
use counter internal to the nf_sockopt_ops structure, we instead use a pointer
to the registering modules owner to do module reference counting when nf_sockopt
calls a modules set/get routine.  This prevents the deadlock by preventing set 4
from happening.

Part 2) Enhances the modprobe utilty so that by default it preforms non-blocking
remove operations (the same way rmmod does), and add an option to explicity
request blocking operation.  So if you select blocking operation in modprobe you
can still cause the above deadlock, but only if you explicity try (and since
root can do any old stupid thing it would like....  :)  ).

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
2007-09-11 11:28:26 +02:00

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#ifndef __LINUX_NETFILTER_H
#define __LINUX_NETFILTER_H
#ifdef __KERNEL__
#include <linux/init.h>
#include <linux/types.h>
#include <linux/skbuff.h>
#include <linux/net.h>
#include <linux/if.h>
#include <linux/wait.h>
#include <linux/list.h>
#endif
#include <linux/compiler.h>
/* Responses from hook functions. */
#define NF_DROP 0
#define NF_ACCEPT 1
#define NF_STOLEN 2
#define NF_QUEUE 3
#define NF_REPEAT 4
#define NF_STOP 5
#define NF_MAX_VERDICT NF_STOP
/* we overload the higher bits for encoding auxiliary data such as the queue
* number. Not nice, but better than additional function arguments. */
#define NF_VERDICT_MASK 0x0000ffff
#define NF_VERDICT_BITS 16
#define NF_VERDICT_QMASK 0xffff0000
#define NF_VERDICT_QBITS 16
#define NF_QUEUE_NR(x) (((x << NF_VERDICT_QBITS) & NF_VERDICT_QMASK) | NF_QUEUE)
/* only for userspace compatibility */
#ifndef __KERNEL__
/* Generic cache responses from hook functions.
<= 0x2000 is used for protocol-flags. */
#define NFC_UNKNOWN 0x4000
#define NFC_ALTERED 0x8000
#endif
#ifdef __KERNEL__
#ifdef CONFIG_NETFILTER
extern void netfilter_init(void);
/* Largest hook number + 1 */
#define NF_MAX_HOOKS 8
struct sk_buff;
struct net_device;
typedef unsigned int nf_hookfn(unsigned int hooknum,
struct sk_buff **skb,
const struct net_device *in,
const struct net_device *out,
int (*okfn)(struct sk_buff *));
struct nf_hook_ops
{
struct list_head list;
/* User fills in from here down. */
nf_hookfn *hook;
struct module *owner;
int pf;
int hooknum;
/* Hooks are ordered in ascending priority. */
int priority;
};
struct nf_sockopt_ops
{
struct list_head list;
int pf;
/* Non-inclusive ranges: use 0/0/NULL to never get called. */
int set_optmin;
int set_optmax;
int (*set)(struct sock *sk, int optval, void __user *user, unsigned int len);
int (*compat_set)(struct sock *sk, int optval,
void __user *user, unsigned int len);
int get_optmin;
int get_optmax;
int (*get)(struct sock *sk, int optval, void __user *user, int *len);
int (*compat_get)(struct sock *sk, int optval,
void __user *user, int *len);
/* Use the module struct to lock set/get code in place */
struct module *owner;
};
/* Each queued (to userspace) skbuff has one of these. */
struct nf_info
{
/* The ops struct which sent us to userspace. */
struct nf_hook_ops *elem;
/* If we're sent to userspace, this keeps housekeeping info */
int pf;
unsigned int hook;
struct net_device *indev, *outdev;
int (*okfn)(struct sk_buff *);
};
/* Function to register/unregister hook points. */
int nf_register_hook(struct nf_hook_ops *reg);
void nf_unregister_hook(struct nf_hook_ops *reg);
int nf_register_hooks(struct nf_hook_ops *reg, unsigned int n);
void nf_unregister_hooks(struct nf_hook_ops *reg, unsigned int n);
/* Functions to register get/setsockopt ranges (non-inclusive). You
need to check permissions yourself! */
int nf_register_sockopt(struct nf_sockopt_ops *reg);
void nf_unregister_sockopt(struct nf_sockopt_ops *reg);
#ifdef CONFIG_SYSCTL
/* Sysctl registration */
struct ctl_table_header *nf_register_sysctl_table(struct ctl_table *path,
struct ctl_table *table);
void nf_unregister_sysctl_table(struct ctl_table_header *header,
struct ctl_table *table);
extern struct ctl_table nf_net_netfilter_sysctl_path[];
extern struct ctl_table nf_net_ipv4_netfilter_sysctl_path[];
#endif /* CONFIG_SYSCTL */
extern struct list_head nf_hooks[NPROTO][NF_MAX_HOOKS];
/* those NF_LOG_* defines and struct nf_loginfo are legacy definitios that will
* disappear once iptables is replaced with pkttables. Please DO NOT use them
* for any new code! */
#define NF_LOG_TCPSEQ 0x01 /* Log TCP sequence numbers */
#define NF_LOG_TCPOPT 0x02 /* Log TCP options */
#define NF_LOG_IPOPT 0x04 /* Log IP options */
#define NF_LOG_UID 0x08 /* Log UID owning local socket */
#define NF_LOG_MASK 0x0f
#define NF_LOG_TYPE_LOG 0x01
#define NF_LOG_TYPE_ULOG 0x02
struct nf_loginfo {
u_int8_t type;
union {
struct {
u_int32_t copy_len;
u_int16_t group;
u_int16_t qthreshold;
} ulog;
struct {
u_int8_t level;
u_int8_t logflags;
} log;
} u;
};
typedef void nf_logfn(unsigned int pf,
unsigned int hooknum,
const struct sk_buff *skb,
const struct net_device *in,
const struct net_device *out,
const struct nf_loginfo *li,
const char *prefix);
struct nf_logger {
struct module *me;
nf_logfn *logfn;
char *name;
};
/* Function to register/unregister log function. */
int nf_log_register(int pf, struct nf_logger *logger);
void nf_log_unregister(struct nf_logger *logger);
void nf_log_unregister_pf(int pf);
/* Calls the registered backend logging function */
void nf_log_packet(int pf,
unsigned int hooknum,
const struct sk_buff *skb,
const struct net_device *in,
const struct net_device *out,
struct nf_loginfo *li,
const char *fmt, ...);
int nf_hook_slow(int pf, unsigned int hook, struct sk_buff **pskb,
struct net_device *indev, struct net_device *outdev,
int (*okfn)(struct sk_buff *), int thresh);
/**
* nf_hook_thresh - call a netfilter hook
*
* Returns 1 if the hook has allowed the packet to pass. The function
* okfn must be invoked by the caller in this case. Any other return
* value indicates the packet has been consumed by the hook.
*/
static inline int nf_hook_thresh(int pf, unsigned int hook,
struct sk_buff **pskb,
struct net_device *indev,
struct net_device *outdev,
int (*okfn)(struct sk_buff *), int thresh,
int cond)
{
if (!cond)
return 1;
#ifndef CONFIG_NETFILTER_DEBUG
if (list_empty(&nf_hooks[pf][hook]))
return 1;
#endif
return nf_hook_slow(pf, hook, pskb, indev, outdev, okfn, thresh);
}
static inline int nf_hook(int pf, unsigned int hook, struct sk_buff **pskb,
struct net_device *indev, struct net_device *outdev,
int (*okfn)(struct sk_buff *))
{
return nf_hook_thresh(pf, hook, pskb, indev, outdev, okfn, INT_MIN, 1);
}
/* Activate hook; either okfn or kfree_skb called, unless a hook
returns NF_STOLEN (in which case, it's up to the hook to deal with
the consequences).
Returns -ERRNO if packet dropped. Zero means queued, stolen or
accepted.
*/
/* RR:
> I don't want nf_hook to return anything because people might forget
> about async and trust the return value to mean "packet was ok".
AK:
Just document it clearly, then you can expect some sense from kernel
coders :)
*/
/* This is gross, but inline doesn't cut it for avoiding the function
call in fast path: gcc doesn't inline (needs value tracking?). --RR */
/* HX: It's slightly less gross now. */
#define NF_HOOK_THRESH(pf, hook, skb, indev, outdev, okfn, thresh) \
({int __ret; \
if ((__ret=nf_hook_thresh(pf, hook, &(skb), indev, outdev, okfn, thresh, 1)) == 1)\
__ret = (okfn)(skb); \
__ret;})
#define NF_HOOK_COND(pf, hook, skb, indev, outdev, okfn, cond) \
({int __ret; \
if ((__ret=nf_hook_thresh(pf, hook, &(skb), indev, outdev, okfn, INT_MIN, cond)) == 1)\
__ret = (okfn)(skb); \
__ret;})
#define NF_HOOK(pf, hook, skb, indev, outdev, okfn) \
NF_HOOK_THRESH(pf, hook, skb, indev, outdev, okfn, INT_MIN)
/* Call setsockopt() */
int nf_setsockopt(struct sock *sk, int pf, int optval, char __user *opt,
int len);
int nf_getsockopt(struct sock *sk, int pf, int optval, char __user *opt,
int *len);
int compat_nf_setsockopt(struct sock *sk, int pf, int optval,
char __user *opt, int len);
int compat_nf_getsockopt(struct sock *sk, int pf, int optval,
char __user *opt, int *len);
/* Packet queuing */
struct nf_queue_handler {
int (*outfn)(struct sk_buff *skb, struct nf_info *info,
unsigned int queuenum, void *data);
void *data;
char *name;
};
extern int nf_register_queue_handler(int pf,
struct nf_queue_handler *qh);
extern int nf_unregister_queue_handler(int pf,
struct nf_queue_handler *qh);
extern void nf_unregister_queue_handlers(struct nf_queue_handler *qh);
extern void nf_reinject(struct sk_buff *skb,
struct nf_info *info,
unsigned int verdict);
/* FIXME: Before cache is ever used, this must be implemented for real. */
extern void nf_invalidate_cache(int pf);
/* Call this before modifying an existing packet: ensures it is
modifiable and linear to the point you care about (writable_len).
Returns true or false. */
extern int skb_make_writable(struct sk_buff **pskb, unsigned int writable_len);
static inline void nf_csum_replace4(__sum16 *sum, __be32 from, __be32 to)
{
__be32 diff[] = { ~from, to };
*sum = csum_fold(csum_partial((char *)diff, sizeof(diff), ~csum_unfold(*sum)));
}
static inline void nf_csum_replace2(__sum16 *sum, __be16 from, __be16 to)
{
nf_csum_replace4(sum, (__force __be32)from, (__force __be32)to);
}
extern void nf_proto_csum_replace4(__sum16 *sum, struct sk_buff *skb,
__be32 from, __be32 to, int pseudohdr);
static inline void nf_proto_csum_replace2(__sum16 *sum, struct sk_buff *skb,
__be16 from, __be16 to, int pseudohdr)
{
nf_proto_csum_replace4(sum, skb, (__force __be32)from,
(__force __be32)to, pseudohdr);
}
struct nf_afinfo {
unsigned short family;
__sum16 (*checksum)(struct sk_buff *skb, unsigned int hook,
unsigned int dataoff, u_int8_t protocol);
void (*saveroute)(const struct sk_buff *skb,
struct nf_info *info);
int (*reroute)(struct sk_buff **skb,
const struct nf_info *info);
int route_key_size;
};
extern struct nf_afinfo *nf_afinfo[];
static inline struct nf_afinfo *nf_get_afinfo(unsigned short family)
{
return rcu_dereference(nf_afinfo[family]);
}
static inline __sum16
nf_checksum(struct sk_buff *skb, unsigned int hook, unsigned int dataoff,
u_int8_t protocol, unsigned short family)
{
struct nf_afinfo *afinfo;
__sum16 csum = 0;
rcu_read_lock();
afinfo = nf_get_afinfo(family);
if (afinfo)
csum = afinfo->checksum(skb, hook, dataoff, protocol);
rcu_read_unlock();
return csum;
}
extern int nf_register_afinfo(struct nf_afinfo *afinfo);
extern void nf_unregister_afinfo(struct nf_afinfo *afinfo);
#define nf_info_reroute(x) ((void *)x + sizeof(struct nf_info))
#include <net/flow.h>
extern void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
static inline void
nf_nat_decode_session(struct sk_buff *skb, struct flowi *fl, int family)
{
#if defined(CONFIG_IP_NF_NAT_NEEDED) || defined(CONFIG_NF_NAT_NEEDED)
void (*decodefn)(struct sk_buff *, struct flowi *);
if (family == AF_INET && (decodefn = ip_nat_decode_session) != NULL)
decodefn(skb, fl);
#endif
}
#ifdef CONFIG_PROC_FS
#include <linux/proc_fs.h>
extern struct proc_dir_entry *proc_net_netfilter;
#endif
#else /* !CONFIG_NETFILTER */
#define NF_HOOK(pf, hook, skb, indev, outdev, okfn) (okfn)(skb)
#define NF_HOOK_COND(pf, hook, skb, indev, outdev, okfn, cond) (okfn)(skb)
static inline int nf_hook_thresh(int pf, unsigned int hook,
struct sk_buff **pskb,
struct net_device *indev,
struct net_device *outdev,
int (*okfn)(struct sk_buff *), int thresh,
int cond)
{
return okfn(*pskb);
}
static inline int nf_hook(int pf, unsigned int hook, struct sk_buff **pskb,
struct net_device *indev, struct net_device *outdev,
int (*okfn)(struct sk_buff *))
{
return 1;
}
struct flowi;
static inline void
nf_nat_decode_session(struct sk_buff *skb, struct flowi *fl, int family) {}
#endif /*CONFIG_NETFILTER*/
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
extern void (*ip_ct_attach)(struct sk_buff *, struct sk_buff *);
extern void nf_ct_attach(struct sk_buff *, struct sk_buff *);
extern void (*nf_ct_destroy)(struct nf_conntrack *);
#else
static inline void nf_ct_attach(struct sk_buff *new, struct sk_buff *skb) {}
#endif
#endif /*__KERNEL__*/
#endif /*__LINUX_NETFILTER_H*/
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