[PATCH 2/3] extensions: libxt_NFLOG: dont truncate log prefix on print/save

[Kyle Bowman <kbowman@cloudflare.com>]

When parsing the rule, use a struct with a layout compatible to that of
struct xt_nflog_info, but with a buffer large enough to contain the
whole 128-character nft prefix.

We always send the nflog-group to the kernel since, for nft, log and
nflog targets are handled by the same kernel module, and are
distinguished by whether they define an nflog-group. Therefore, we must
send the group even if it is zero, or the kernel will configure the
target as a log, not an nflog.

Changes to nft_is_expr_compatible were made since only targets which
have an `nflog-group` are compatible. Since nflog targets are
distinguished by having an nflog-group, we ignore targets without one.

We also set the copy-len flag if the snap-len is set since without this,
iptables will mistake `nflog-size` for `nflog-range`.

Signed-off-by: Kyle Bowman <kbowman@cloudflare.com>
Signed-off-by: Alex Forster <aforster@cloudflare.com>
Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
---
 iptables/nft-shared.c | 58 +++++++++++++++++++++++++++++++++++++++++++
 iptables/nft.c        |  4 +++
 2 files changed, 62 insertions(+)

diff --git a/iptables/nft-shared.c b/iptables/nft-shared.c
index 4253b081..c164d140 100644
--- a/iptables/nft-shared.c
+++ b/iptables/nft-shared.c
@@ -20,8 +20,10 @@
 
 #include <xtables.h>
 
+#include <linux/netfilter/nf_log.h>
 #include <linux/netfilter/xt_comment.h>
 #include <linux/netfilter/xt_limit.h>
+#include <linux/netfilter/xt_NFLOG.h>
 
 #include <libmnl/libmnl.h>
 #include <libnftnl/rule.h>
@@ -595,6 +597,60 @@ static void nft_parse_limit(struct nft_xt_ctx *ctx, struct nftnl_expr *e)
 		ctx->h->ops->parse_match(match, ctx->cs);
 }
 
+static void nft_parse_log(struct nft_xt_ctx *ctx, struct nftnl_expr *e)
+{
+	struct xtables_target *target;
+	struct xt_entry_target *t;
+	size_t target_size;
+	/*
+	* In order to handle the longer log-prefix supported by nft, instead of
+	* using struct xt_nflog_info, we use a struct with a compatible layout, but
+	* a larger buffer for the prefix.
+	*/
+	struct xt_nflog_info_nft {
+		__u32 len;
+		__u16 group;
+		__u16 threshold;
+		__u16 flags;
+		__u16 pad;
+		char  prefix[NF_LOG_PREFIXLEN];
+	} info = {
+		.group     = nftnl_expr_get_u16(e, NFTNL_EXPR_LOG_GROUP),
+		.threshold = nftnl_expr_get_u16(e, NFTNL_EXPR_LOG_QTHRESHOLD),
+	};
+	if (nftnl_expr_is_set(e, NFTNL_EXPR_LOG_SNAPLEN)) {
+		info.len = nftnl_expr_get_u32(e, NFTNL_EXPR_LOG_SNAPLEN);
+		info.flags = XT_NFLOG_F_COPY_LEN;
+	}
+	if (nftnl_expr_is_set(e, NFTNL_EXPR_LOG_PREFIX)) {
+		snprintf(info.prefix, sizeof(info.prefix), "%s",
+				nftnl_expr_get_str(e, NFTNL_EXPR_LOG_PREFIX));
+	}
+
+	target = xtables_find_target("NFLOG", XTF_TRY_LOAD);
+	if (target == NULL)
+		return;
+
+	target_size = XT_ALIGN(sizeof(struct xt_entry_target)) +
+		XT_ALIGN(sizeof(struct xt_nflog_info_nft));
+
+	t = xtables_calloc(1, target_size);
+	t->u.target_size = target_size;
+	strcpy(t->u.user.name, target->name);
+	t->u.user.revision = target->revision;
+
+	target->t = t;
+
+	struct xt_nflog_info *info = xtables_malloc(sizeof(struct xt_nflog_info));
+	info->group = group;
+	info->len = snaplen;
+	info->threshold = qthreshold;
+
+	memcpy(&target->t->data, &info, sizeof(info));
+
+	ctx->h->ops->parse_target(target, ctx->cs);
+}
+
 static void nft_parse_lookup(struct nft_xt_ctx *ctx, struct nft_handle *h,
 			     struct nftnl_expr *e)
 {
@@ -644,6 +700,8 @@ void nft_rule_to_iptables_command_state(struct nft_handle *h,
 			nft_parse_limit(&ctx, expr);
 		else if (strcmp(name, "lookup") == 0)
 			nft_parse_lookup(&ctx, h, expr);
+		else if (strcmp(name, "log") == 0)
+			nft_parse_log(&ctx, expr);
 
 		expr = nftnl_expr_iter_next(iter);
 	}
diff --git a/iptables/nft.c b/iptables/nft.c
index aebbf674..e9875f28 100644
--- a/iptables/nft.c
+++ b/iptables/nft.c
@@ -3515,6 +3515,10 @@ static int nft_is_expr_compatible(struct nftnl_expr *expr, void *data)
 	    nftnl_expr_get_u32(expr, NFTNL_EXPR_LIMIT_FLAGS) == 0)
 		return 0;
 
+	if (!strcmp(name, "log") &&
+	    nftnl_expr_is_set(expr, NFTNL_EXPR_LOG_GROUP))
+		return 0;
+
 	return -1;
 }
 
-- 
2.20.1