[PATCH 5.14 087/172] netfilter: log: work around missing softdep backend module

Greg Kroah-Hartman
2021-10-04T13:34:31Z

From: Florian Westphal <fw@strlen.de>

[ Upstream commit b53deef054e58fe4f37c66211b8ece9f8fc1aa13 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.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 272bcdb1392d..f69cc73c5813 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 2ff75f7637b0..f39244f9c0ed 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 fb5793208059..e660c3710a10 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)
--
2.33.0