From b53deef054e58fe4f37c66211b8ece9f8fc1aa13 Mon Sep 17 00:00:00 2001 From: Florian Westphal <fw@strlen.de> Date: Fri, 17 Sep 2021 18:50:17 +0200 Subject: [PATCH] netfilter: log: work around missing softdep backend module iptables/nftables has two types of log modules: 1. backend, e.g. nf_log_syslog, which implement the functionality 2. frontend, e.g. xt_LOG or nft_log, which call the functionality provided by backend based on nf_tables or xtables rule set. Problem is that the request_module() call to load the backed in nf_logger_find_get() might happen with nftables transaction mutex held in case the call path is via nf_tables/nft_compat. This can cause deadlocks (see 'Fixes' tags for details). The chosen solution as to let modprobe deal with this by adding 'pre: ' soft dep tag to xt_LOG (to load the syslog backend) and xt_NFLOG (to load nflog backend). Eric reports that this breaks on systems with older modprobe that doesn't support softdeps. Another, similar issue occurs when someone either insmods xt_(NF)LOG directly or unloads the backend module (possible if no log frontend is in use): because the frontend module is already loaded, modprobe is not invoked again so the softdep isn't evaluated. Add a workaround: If nf_logger_find_get() returns -ENOENT and call is not via nft_compat, load the backend explicitly and try again. Else, let nft_compat ask for deferred request_module via nf_tables infra. Softdeps are kept in-place, so with newer modprobe the dependencies are resolved from userspace. Fixes: cefa31a9d461 ("netfilter: nft_log: perform module load from nf_tables") Fixes: a38b5b56d6f4 ("netfilter: nf_log: add module softdeps") Reported-and-tested-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> --- net/netfilter/nft_compat.c | 17 ++++++++++++++++- net/netfilter/xt_LOG.c | 10 +++++++++- net/netfilter/xt_NFLOG.c | 10 +++++++++- 3 files changed, 34 insertions(+), 3 deletions(-) diff --git a/net/netfilter/nft_compat.c b/net/netfilter/nft_compat.c index 272bcdb1392df..f69cc73c58130 100644 --- a/net/netfilter/nft_compat.c +++ b/net/netfilter/nft_compat.c @@ -19,6 +19,7 @@ #include <linux/netfilter_bridge/ebtables.h> #include <linux/netfilter_arp/arp_tables.h> #include <net/netfilter/nf_tables.h> +#include <net/netfilter/nf_log.h> /* Used for matches where *info is larger than X byte */ #define NFT_MATCH_LARGE_THRESH 192 @@ -257,8 +258,22 @@ nft_target_init(const struct nft_ctx *ctx, const struct nft_expr *expr, nft_compat_wait_for_destructors(); ret = xt_check_target(&par, size, proto, inv); - if (ret < 0) + if (ret < 0) { + if (ret == -ENOENT) { + const char *modname = NULL; + + if (strcmp(target->name, "LOG") == 0) + modname = "nf_log_syslog"; + else if (strcmp(target->name, "NFLOG") == 0) + modname = "nfnetlink_log"; + + if (modname && + nft_request_module(ctx->net, "%s", modname) == -EAGAIN) + return -EAGAIN; + } + return ret; + } /* The standard target cannot be used */ if (!target->target) diff --git a/net/netfilter/xt_LOG.c b/net/netfilter/xt_LOG.c index 2ff75f7637b09..f39244f9c0ed9 100644 --- a/net/netfilter/xt_LOG.c +++ b/net/netfilter/xt_LOG.c @@ -44,6 +44,7 @@ log_tg(struct sk_buff *skb, const struct xt_action_param *par) static int log_tg_check(const struct xt_tgchk_param *par) { const struct xt_log_info *loginfo = par->targinfo; + int ret; if (par->family != NFPROTO_IPV4 && par->family != NFPROTO_IPV6) return -EINVAL; @@ -58,7 +59,14 @@ static int log_tg_check(const struct xt_tgchk_param *par) return -EINVAL; } - return nf_logger_find_get(par->family, NF_LOG_TYPE_LOG); + ret = nf_logger_find_get(par->family, NF_LOG_TYPE_LOG); + if (ret != 0 && !par->nft_compat) { + request_module("%s", "nf_log_syslog"); + + ret = nf_logger_find_get(par->family, NF_LOG_TYPE_LOG); + } + + return ret; } static void log_tg_destroy(const struct xt_tgdtor_param *par) diff --git a/net/netfilter/xt_NFLOG.c b/net/netfilter/xt_NFLOG.c index fb57932080598..e660c3710a109 100644 --- a/net/netfilter/xt_NFLOG.c +++ b/net/netfilter/xt_NFLOG.c @@ -42,13 +42,21 @@ nflog_tg(struct sk_buff *skb, const struct xt_action_param *par) static int nflog_tg_check(const struct xt_tgchk_param *par) { const struct xt_nflog_info *info = par->targinfo; + int ret; if (info->flags & ~XT_NFLOG_MASK) return -EINVAL; if (info->prefix[sizeof(info->prefix) - 1] != '\0') return -EINVAL; - return nf_logger_find_get(par->family, NF_LOG_TYPE_ULOG); + ret = nf_logger_find_get(par->family, NF_LOG_TYPE_ULOG); + if (ret != 0 && !par->nft_compat) { + request_module("%s", "nfnetlink_log"); + + ret = nf_logger_find_get(par->family, NF_LOG_TYPE_ULOG); + } + + return ret; } static void nflog_tg_destroy(const struct xt_tgdtor_param *par) -- 2.39.5