linux-kernel - Re: [PATCH] drivers: binderfs: fix memory leak in binderfs_fill

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Date:   Fri, 12 Aug 2022 21:48:40 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Christian Brauner <brauner@...nel.org>
Cc:     Dongliang Mu <dzm91@...t.edu.cn>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Carlos Llamas <cmllamas@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        syzkaller <syzkaller@...glegroups.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers: binderfs: fix memory leak in binderfs_fill_super

On Fri, Aug 12, 2022 at 9:41 PM Christian Brauner <brauner@...nel.org> wrote:
>
> On Fri, Aug 12, 2022 at 09:21:24PM +0800, Dongliang Mu wrote:
> > From: Dongliang Mu <mudongliangabcd@...il.com>
> >
> > In binderfs_fill_super, if s_root is not successfully initialized by
> > d_make_root, the previous allocated s_sb_info will not be freed since
> > generic_shutdown_super first checks if sb->s_root and then does
> > put_super operation. The put_super operation calls binderfs_put_super
> > to deallocate s_sb_info and put ipc_ns. This will lead to memory leak
> > in binderfs_fill_super.
> >
> > Fix this by invoking binderfs_put_super at error sites before s_root
> > is successfully initialized.
> >
> > Fixes: 095cf502b31e ("binderfs: port to new mount api")
> > Reported-by: syzkaller <syzkaller@...glegroups.com>
> > Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
> > ---
>
> Seems right but where's the full syzbot link to the issue?
> Also, wouldn't (untested) sm like the below be better?:

I originally would like to change the order to object initialization,
but I am not sure if they can be exchanged since many *_fill_super are
ended with d_make_root.

If you are sure about this exchange, I can resubmit a v2 patch.

>
> diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
> index 588d753a7a19..4582b043d21e 100644
> --- a/drivers/android/binderfs.c
> +++ b/drivers/android/binderfs.c
> @@ -692,6 +692,15 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
>         sb->s_magic = BINDERFS_SUPER_MAGIC;
>         sb->s_op = &binderfs_super_ops;
>         sb->s_time_gran = 1;
> +       sb->s_fs_info = NULL;
> +
> +       inode = new_inode(sb);
> +       if (!inode)
> +               return -ENOMEM;
> +
> +       sb->s_root = d_make_root(inode);
> +       if (!sb->s_root)
> +               return -ENOMEM;
>
>         sb->s_fs_info = kzalloc(sizeof(struct binderfs_info), GFP_KERNEL);
>         if (!sb->s_fs_info)
> @@ -709,10 +718,6 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
>         info->mount_opts.max = ctx->max;
>         info->mount_opts.stats_mode = ctx->stats_mode;
>
> -       inode = new_inode(sb);
> -       if (!inode)
> -               return -ENOMEM;
> -
>         inode->i_ino = FIRST_INODE;
>         inode->i_fop = &simple_dir_operations;
>         inode->i_mode = S_IFDIR | 0755;
> @@ -720,10 +725,6 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
>         inode->i_op = &binderfs_dir_inode_operations;
>         set_nlink(inode, 2);
>
> -       sb->s_root = d_make_root(inode);
> -       if (!sb->s_root)
> -               return -ENOMEM;
> -
>         ret = binderfs_binder_ctl_create(sb);
>         if (ret)
>                 return ret;
>
> >  drivers/android/binderfs.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
> > index 588d753a7a19..20f5bc77495f 100644
> > --- a/drivers/android/binderfs.c
> > +++ b/drivers/android/binderfs.c
> > @@ -710,8 +710,10 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
> >       info->mount_opts.stats_mode = ctx->stats_mode;
> >
> >       inode = new_inode(sb);
> > -     if (!inode)
> > +     if (!inode) {
> > +             binderfs_put_super(sb);
> >               return -ENOMEM;
> > +     }
> >
> >       inode->i_ino = FIRST_INODE;
> >       inode->i_fop = &simple_dir_operations;
> > @@ -721,8 +723,10 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
> >       set_nlink(inode, 2);
> >
> >       sb->s_root = d_make_root(inode);
> > -     if (!sb->s_root)
> > +     if (!sb->s_root) {
> > +             binderfs_put_super(sb);
> >               return -ENOMEM;
> > +     }
> >
> >       ret = binderfs_binder_ctl_create(sb);
> >       if (ret)
> > --
> > 2.25.1
> >