Re: [PATCH] mm/damon/dbgfs: fix memory leak when using debugfs_lookup()

[SeongJae Park <sj@kernel.org>]

Hi Andrew and Greg!

On Fri, 2 Sep 2022 09:17:03 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:

> On Fri,  2 Sep 2022 14:56:31 +0200 Greg Kroah-Hartman <gregkh@linuxfoundation.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().

Thank you for finding this bug and posting this patch, Greg!

> > 
> > ...
> >
> 
> Fixes: 75c1c2b53c78b, I assume.

Correct, Andrew.

Fixes: 75c1c2b53c78b ("mm/damon/dbgfs: support multiple contexts")
Cc: <stable@vger.kernel.org> # 5.15.x

> 
> > --- 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

Good catch.

> 
> --- 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;

Shouldn't we also do 'ret = -ENOMEM;' before 'godo 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;

ditto.

>  
>  	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,
> _


Thanks,
SJ