2022-01-02 11:22:00

by SeongJae Park

Subject: [PATCH for-v5.15.x] mm/damon/dbgfs: fix 'struct pid' leaks in 'dbgfs_target_ids_write()'

commit ebb3f994dd92f8fb4d70c7541091216c1e10cb71 upstream.

DAMON debugfs interface increases the reference counts of 'struct pid's
for targets from the 'target_ids' file write callback
('dbgfs_target_ids_write()'), but decreases the counts only in DAMON
monitoring termination callback ('dbgfs_before_terminate()').

Therefore, when 'target_ids' file is repeatedly written without DAMON
monitoring start/termination, the reference count is not decreased and
therefore memory for the 'struct pid' cannot be freed. This commit
fixes this issue by decreasing the reference counts when 'target_ids' is
written.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 4bc05954d007 ("mm/damon: implement a debugfs-based user space interface")
Signed-off-by: SeongJae Park <[email protected]>
Cc: <[email protected]> # 5.15.x
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
---
This is a backport of a DAMON fix that merged in the mainline, for
v5.15.x stable series.

mm/damon/dbgfs.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index d3bc110430f9..36624990b577 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -185,6 +185,7 @@ static ssize_t dbgfs_target_ids_write(struct file *file,
const char __user *buf, size_t count, loff_t *ppos)
{
struct damon_ctx *ctx = file->private_data;
+ struct damon_target *t, *next_t;
char *kbuf, *nrs;
unsigned long *targets;
ssize_t nr_targets;
@@ -224,6 +225,13 @@ static ssize_t dbgfs_target_ids_write(struct file *file,
goto unlock_out;
}

+ /* remove previously set targets */
+ damon_for_each_target_safe(t, next_t, ctx) {
+ if (targetid_is_pid(ctx))
+ put_pid((struct pid *)t->id);
+ damon_destroy_target(t);
+ }
+
err = damon_set_targets(ctx, targets, nr_targets);
if (err) {
if (targetid_is_pid(ctx))
--
2.17.1

2022-01-03 09:46:14

by Greg Kroah-Hartman

Subject: Re: [PATCH for-v5.15.x] mm/damon/dbgfs: fix 'struct pid' leaks in 'dbgfs_target_ids_write()'

On Sun, Jan 02, 2022 at 11:21:41AM +0000, SeongJae Park wrote:
> commit ebb3f994dd92f8fb4d70c7541091216c1e10cb71 upstream.
>
> DAMON debugfs interface increases the reference counts of 'struct pid's
> for targets from the 'target_ids' file write callback
> ('dbgfs_target_ids_write()'), but decreases the counts only in DAMON
> monitoring termination callback ('dbgfs_before_terminate()').
>
> Therefore, when 'target_ids' file is repeatedly written without DAMON
> monitoring start/termination, the reference count is not decreased and
> therefore memory for the 'struct pid' cannot be freed. This commit
> fixes this issue by decreasing the reference counts when 'target_ids' is
> written.
>
> Link: https://lkml.kernel.org/r/[email protected]
> Fixes: 4bc05954d007 ("mm/damon: implement a debugfs-based user space interface")
> Signed-off-by: SeongJae Park <[email protected]>
> Cc: <[email protected]> # 5.15.x
> Signed-off-by: Andrew Morton <[email protected]>
> Signed-off-by: Linus Torvalds <[email protected]>
> ---
> This is a backport of a DAMON fix that merged in the mainline, for
> v5.15.x stable series.

Now queued up, thanks.

greg k-h