On Thu, 20 Feb 2025 11:15:28 +0800 Adrian Huang <[email protected]> wrote:
> From: Adrian Huang <[email protected]> > > 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 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 <[email protected]> Looks good to me. Acked-by: Masami Hiramatsu (Google) <[email protected]> Thank you, > --- > Changelog v2: > - Per Steven's suggestion: Add a comment to describe why to free memory > in s_next(). > - Per Steven's suggestion: Change the variable 'p' to 'v' in s_stop() > > --- > kernel/trace/trace_events.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c > index 4cb275316e51..513de9ceb80e 100644 > --- a/kernel/trace/trace_events.c > +++ b/kernel/trace/trace_events.c > @@ -1591,6 +1591,13 @@ s_next(struct seq_file *m, void *v, loff_t *pos) > return iter; > #endif > > + /* > + * The iter is allocated in s_start() and passed via the 'v' > + * parameter. To stop the iterator, NULL must be returned. But > + * the return value is what the 'v' parameter in s_stop() receives > + * and frees. Free iter here as it will no longer be used. > + */ > + kfree(iter); > return NULL; > } > > @@ -1667,9 +1674,9 @@ static int s_show(struct seq_file *m, void *v) > } > #endif > > -static void s_stop(struct seq_file *m, void *p) > +static void s_stop(struct seq_file *m, void *v) > { > - kfree(p); > + kfree(v); > t_stop(m, NULL); > } > > -- > 2.34.1 > -- Masami Hiramatsu (Google) <[email protected]>
