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/20211229124029.23348-1-sj@kernel.org
Fixes: 4bc05954d007 ("mm/damon: implement a debugfs-based user space interface")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[5.15+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index d3bc110..3662499 100644 (file)
--- 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))