linux-kernel - Re: [PATCH] mm/damon/dbgfs: fix memory leak when using debugfs

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Date:   Fri, 2 Sep 2022 09:17:03 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     SeongJae Park <sj@...nel.org>, linux-kernel@...r.kernel.org,
        damon@...ts.linux.dev, linux-mm@...ck.org,
        stable <stable@...nel.org>
Subject: Re: [PATCH] mm/damon/dbgfs: fix memory leak when using
 debugfs_lookup()

On Fri,  2 Sep 2022 14:56:31 +0200 Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:

> When calling debugfs_lookup() the result must have dput() called on it,
> otherwise the memory will leak over time.  Fix this up by properly
> calling dput().
> 
> ...
>

Fixes: 75c1c2b53c78b, I assume.

> --- a/mm/damon/dbgfs.c
> +++ b/mm/damon/dbgfs.c
> @@ -915,6 +915,7 @@ static int dbgfs_rm_context(char *name)
>  		new_ctxs[j++] = dbgfs_ctxs[i];
>  	}
>  
> +	dput(dir);
>  	kfree(dbgfs_dirs);
>  	kfree(dbgfs_ctxs);
>  

dput() is also needed if either of the kmalloc_array() calls fail?
Maybe something like

--- a/mm/damon/dbgfs.c~a
+++ a/mm/damon/dbgfs.c
@@ -884,6 +884,7 @@ static int dbgfs_rm_context(char *name)
 	struct dentry *root, *dir, **new_dirs;
 	struct damon_ctx **new_ctxs;
 	int i, j;
+	int ret = 0;
 
 	if (damon_nr_running_ctxs())
 		return -EBUSY;
@@ -899,14 +900,12 @@ static int dbgfs_rm_context(char *name)
 	new_dirs = kmalloc_array(dbgfs_nr_ctxs - 1, sizeof(*dbgfs_dirs),
 			GFP_KERNEL);
 	if (!new_dirs)
-		return -ENOMEM;
+		goto out_dput;
 
 	new_ctxs = kmalloc_array(dbgfs_nr_ctxs - 1, sizeof(*dbgfs_ctxs),
 			GFP_KERNEL);
-	if (!new_ctxs) {
-		kfree(new_dirs);
-		return -ENOMEM;
-	}
+	if (!new_ctxs)
+		goto out_new_dirs;
 
 	for (i = 0, j = 0; i < dbgfs_nr_ctxs; i++) {
 		if (dbgfs_dirs[i] == dir) {
@@ -925,7 +924,13 @@ static int dbgfs_rm_context(char *name)
 	dbgfs_ctxs = new_ctxs;
 	dbgfs_nr_ctxs--;
 
-	return 0;
+	goto out_dput;
+
+out_new_dirs:
+	kfree(new_dirs);
+out_dput:
+	dput(dir);
+	return ret;
 }
 
 static ssize_t dbgfs_rm_context_write(struct file *file,
_