[PATCH] tracing: fix kstrdup leak on repeated trigger keywords

[Tang Bin]

parse_assignment() overwrites
attrs->keys_str/vals_str/sort_key_str/name/clock with a fresh kstrdup()
without freeing a previously assigned value. A hist trigger string with
repeated keywords (e.g. 'keys=pid:keys=comm') leaks the earlier allocation
each time. kfree() the old pointer before reassigning (attrs is kzalloc'd
so the first call sees NULL).

Fixes: b527b638fd63 ("tracing: Simplify assignment parsing for hist triggers")
Signed-off-by: Tang Bin <tangbin@xxxxxxxxxxxxxxxxxxxx>
---
 kernel/trace/trace_events_hist.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 8af97fd4e..4ce857072 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1481,6 +1481,7 @@ static int parse_assignment(struct trace_array *tr,
 
 	if ((len = str_has_prefix(str, "key=")) ||
 	    (len = str_has_prefix(str, "keys="))) {
+		kfree(attrs->keys_str);
 		attrs->keys_str = kstrdup(str + len, GFP_KERNEL);
 		if (!attrs->keys_str) {
 			ret = -ENOMEM;
@@ -1489,18 +1490,21 @@ static int parse_assignment(struct trace_array *tr,
 	} else if ((len = str_has_prefix(str, "val=")) ||
 		   (len = str_has_prefix(str, "vals=")) ||
 		   (len = str_has_prefix(str, "values="))) {
+		kfree(attrs->vals_str);
 		attrs->vals_str = kstrdup(str + len, GFP_KERNEL);
 		if (!attrs->vals_str) {
 			ret = -ENOMEM;
 			goto out;
 		}
 	} else if ((len = str_has_prefix(str, "sort="))) {
+		kfree(attrs->sort_key_str);
 		attrs->sort_key_str = kstrdup(str + len, GFP_KERNEL);
 		if (!attrs->sort_key_str) {
 			ret = -ENOMEM;
 			goto out;
 		}
 	} else if (str_has_prefix(str, "name=")) {
+		kfree(attrs->name);
 		attrs->name = kstrdup(str, GFP_KERNEL);
 		if (!attrs->name) {
 			ret = -ENOMEM;
@@ -1510,6 +1514,7 @@ static int parse_assignment(struct trace_array *tr,
 		str += len;
 
 		str = strstrip(str);
+		kfree(attrs->clock);
 		attrs->clock = kstrdup(str, GFP_KERNEL);
 		if (!attrs->clock) {
 			ret = -ENOMEM;
-- 
2.52.0.windows.1