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netfilter: nft_log: perform module load from nf_tables

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modprobe calls from the nf_logger_find_get() API causes deadlock in very
special cases because they occur with the nf_tables transaction mutex held.

In the specific case of nf_log, deadlock is via:

 A nf_tables -> transaction mutex -> nft_log -> modprobe -> nf_log_syslog \
	    -> pernet_ops rwsem -> wait for C
 B netlink event -> rtnl_mutex -> nf_tables transaction mutex -> wait for A
 C close() -> ip6mr_sk_done -> rtnl_mutex -> wait for B

Earlier patch added NFLOG/xt_LOG module softdeps to avoid the need to load
the backend module during a transaction.

For nft_log we would have to add a softdep for both nfnetlink_log or
nf_log_syslog, since we do not know in advance which of the two backends
are going to be configured.

This defers the modprobe op until after the transaction mutex is released.

Tested-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2021-03-25 18:25:12 +01:00 committed by Pablo Neira Ayuso
parent a38b5b56d6
commit cefa31a9d4
4 changed files with 27 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/net/netfilter/nf_tables.h
View File

@ -1562,4 +1562,9 @@ void nf_tables_trans_destroy_flush_work(void);
int nf_msecs_to_jiffies64(const struct nlattr *nla, u64 *result);
__be64 nf_jiffies64_to_msecs(u64 input);
#ifdef CONFIG_MODULES
__printf(2, 3) int nft_request_module(struct net *net, const char *fmt, ...);
#else
static inline int nft_request_module(struct net *net, const char *fmt, ...) { return -ENOENT; }
#endif
#endif /* _NET_NF_TABLES_H */

3
net/netfilter/nf_log.c
View File

@ -170,9 +170,6 @@ int nf_logger_find_get(int pf, enum nf_log_type type)
return 0;
}
if (rcu_access_pointer(loggers[pf][type]) == NULL)
request_module("nf-logger-%u-%u", pf, type);
rcu_read_lock();
logger = rcu_dereference(loggers[pf][type]);
if (logger == NULL)

3
net/netfilter/nf_tables_api.c
View File

@ -586,7 +586,7 @@ struct nft_module_request {
};
#ifdef CONFIG_MODULES
static __printf(2, 3) int nft_request_module(struct net *net, const char *fmt,
__printf(2, 3) int nft_request_module(struct net *net, const char *fmt,
...)
{
char module_name[MODULE_NAME_LEN];
@ -620,6 +620,7 @@ static __printf(2, 3) int nft_request_module(struct net *net, const char *fmt,
return -EAGAIN;
}
EXPORT_SYMBOL_GPL(nft_request_module);
#endif
static void lockdep_nfnl_nft_mutex_not_held(void)

20
net/netfilter/nft_log.c
View File

@ -128,6 +128,20 @@ static const struct nla_policy nft_log_policy[NFTA_LOG_MAX + 1] = {
[NFTA_LOG_FLAGS] = { .type = NLA_U32 },
};
static int nft_log_modprobe(struct net *net, enum nf_log_type t)
{
switch (t) {
case NF_LOG_TYPE_LOG:
return nft_request_module(net, "%s", "nf_log_syslog");
case NF_LOG_TYPE_ULOG:
return nft_request_module(net, "%s", "nfnetlink_log");
case NF_LOG_TYPE_MAX:
break;
}
return -ENOENT;
}
static int nft_log_init(const struct nft_ctx *ctx,
const struct nft_expr *expr,
const struct nlattr * const tb[])
@ -197,8 +211,12 @@ static int nft_log_init(const struct nft_ctx *ctx,
return 0;
err = nf_logger_find_get(ctx->family, li->type);
if (err < 0)
if (err < 0) {
if (nft_log_modprobe(ctx->net, li->type) == -EAGAIN)
err = -EAGAIN;
goto err1;
}
return 0;