src: fix broken output handling

In 948fa3b ("Extend accounting capabilities to support quotas"), the
error handling of snprintf is incorrect since this function may
return -1 on error. Add a new SNPRINTF_CHECK() macro to offload the
complicated handling of snprintf.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/internal.h b/src/internal.h
index 2106401..f0cc2e1 100644
--- a/src/internal.h
+++ b/src/internal.h
@@ -21,4 +21,15 @@
 #	endif
 #endif
 
+#define SNPRINTF_CHECK(ret, rem, offset, len)			\
+do {								\
+	if (ret < 0)						\
+		return ret;					\
+	len += ret;						\
+	if (ret > rem)						\
+		ret = rem;					\
+	offset += ret;						\
+	rem -= ret;						\
+} while (0)
+
 #endif