[PATCH 1/1] tracing: Fix memory leak when reading set_event file

From: Adrian Huang
Date: Wed Feb 19 2025 - 05:43:02 EST


From: Adrian Huang <ahuang12@xxxxxxxxxx>

kmemleak reports the following memory leak after reading set_event file:

# cat /sys/kernel/tracing/set_event

# cat /sys/kernel/debug/kmemleak
unreferenced object 0xff110001234449e0 (size 16):
comm "cat", pid 13645, jiffies 4294981880
hex dump (first 16 bytes):
01 00 00 00 00 00 00 00 a8 71 e7 84 ff ff ff ff .........q......
backtrace (crc c43abbc):
__kmalloc_cache_noprof+0x3ca/0x4b0
s_start+0x72/0x2d0
seq_read_iter+0x265/0x1080
seq_read+0x2c9/0x420
vfs_read+0x166/0xc30
ksys_read+0xf4/0x1d0
do_syscall_64+0x79/0x150
entry_SYSCALL_64_after_hwframe+0x76/0x7e

The issue can be reproduced regardless of whether set_event is empty or
not. Here is an example about the valid content of set_event.

# cat /sys/kernel/tracing/set_event
sched:sched_process_fork
sched:sched_switch
sched:sched_wakeup
*:*:mod:trace_events_sample

The root cause is that s_next() returns NULL when nothing is found.
This results in s_stop() attempting to free a NULL pointer because its
parameter p is NULL.

Fix the issue by freeing the memory appropriately when s_next() fails
to find anything.

Fixes: b355247df104 ("tracing: Cache ":mod:" events for modules not loaded yet")
Signed-off-by: Adrian Huang <ahuang12@xxxxxxxxxx>
---
kernel/trace/trace_events.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 4cb275316e51..c76353ad0a4e 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1591,6 +1591,7 @@ s_next(struct seq_file *m, void *v, loff_t *pos)
return iter;
#endif

+ kfree(iter);
return NULL;
}

--
2.34.1