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List:       git-commits-head
Subject:    mm/damon/dbgfs: fix 'struct pid' leaks in 'dbgfs_target_ids_write()'
From:       Linux Kernel Mailing List <linux-kernel () vger ! kernel ! org>
Date:       2021-12-31 17:51:13
Message-ID: git-mailbomb-linux-master-ebb3f994dd92f8fb4d70c7541091216c1e10cb71 () kernel ! org
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Commit:     ebb3f994dd92f8fb4d70c7541091216c1e10cb71
Parent:     f5c73297181c6b3ad76537bad98eaad6d29b9333
Refname:    refs/heads/master
Web:        https://git.kernel.org/torvalds/c/ebb3f994dd92f8fb4d70c7541091216c1e10cb71
Author:     SeongJae Park <sj@kernel.org>
AuthorDate: Thu Dec 30 20:12:34 2021 -0800
Committer:  Linus Torvalds <torvalds@linux-foundation.org>
CommitDate: Fri Dec 31 09:20:12 2021 -0800

    mm/damon/dbgfs: fix 'struct pid' leaks in 'dbgfs_target_ids_write()'
    
    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>
---
 mm/damon/dbgfs.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 4fbd729edc9e7..ad65436756aff 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -353,6 +353,7 @@ 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;
 	bool id_is_pid = true;
 	char *kbuf, *nrs;
 	unsigned long *targets;
@@ -397,8 +398,12 @@ static ssize_t dbgfs_target_ids_write(struct file *file,
 		goto unlock_out;
 	}
 
-	/* remove targets with previously-set primitive */
-	damon_set_targets(ctx, NULL, 0);
+	/* 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);
+	}
 
 	/* Configure the context for the address space type */
 	if (id_is_pid)
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