diff --git a/net/netfilter/nf_log.c b/net/netfilter/nf_log.c
index 4264570475788be388e603c1bc70330c812d0eb3..2c47f9ec35117c73a8add4724ca8db5f0e50f0ec 100644
--- a/net/netfilter/nf_log.c
+++ b/net/netfilter/nf_log.c
@@ -424,6 +424,10 @@ static int nf_log_proc_dostring(struct ctl_table *table, int write,
 	if (write) {
 		struct ctl_table tmp = *table;
 
+		/* proc_dostring() can append to existing strings, so we need to
+		 * initialize it as an empty string.
+		 */
+		buf[0] = '\0';
 		tmp.data = buf;
 		r = proc_dostring(&tmp, write, buffer, lenp, ppos);
 		if (r)