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

SeongJae Park
2022-09-02T18:12:35Z

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