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mm/damon/dbgfs: fix 'struct pid' leaks in 'dbgfs_target_ids_write()'

PATCH In review SeongJae Park 2 participants 2 messages Jan 2, 2022 – Jan 3, 2022

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Stable branch Memory management DAMON
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SeongJae Park

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PATCH 1/1 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] open here
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(+)
mm/damon/dbgfs.c +8 -0
index d3bc110430f9..36624990b577 100644
@@ -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))
Signature · 1 line
2.17.1
maintainer
#1 lore raw
Quoted 19 lines · SeongJae Park

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] open here
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]>
Quoted 3 lines

---
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