netdev - Re: [PATCH v6 bpf-next 02/13] bpf: add BPF token delegation mount options to BPF FS

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Message-ID: <CAEf4BzakCJHvPibso_bsPhYdXo9YyHuwPiLebLdvq0DonAFJ+Q@mail.gmail.com>
Date: Wed, 11 Oct 2023 17:30:17 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Hou Tao <houtao@...weicloud.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org, netdev@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-security-module@...r.kernel.org, 
	keescook@...omium.org, brauner@...nel.org, lennart@...ttering.net, 
	kernel-team@...a.com, sargun@...gun.me
Subject: Re: [PATCH v6 bpf-next 02/13] bpf: add BPF token delegation mount
 options to BPF FS

On Tue, Oct 10, 2023 at 12:09 AM Hou Tao <houtao@...weicloud.com> wrote:
>
>
>
> On 9/28/2023 6:57 AM, Andrii Nakryiko wrote:
> > Add few new mount options to BPF FS that allow to specify that a given
> > BPF FS instance allows creation of BPF token (added in the next patch),
> > and what sort of operations are allowed under BPF token. As such, we get
> > 4 new mount options, each is a bit mask
> >   - `delegate_cmds` allow to specify which bpf() syscall commands are
> >     allowed with BPF token derived from this BPF FS instance;
> >   - if BPF_MAP_CREATE command is allowed, `delegate_maps` specifies
> >     a set of allowable BPF map types that could be created with BPF token;
> >   - if BPF_PROG_LOAD command is allowed, `delegate_progs` specifies
> >     a set of allowable BPF program types that could be loaded with BPF token;
> >   - if BPF_PROG_LOAD command is allowed, `delegate_attachs` specifies
> >     a set of allowable BPF program attach types that could be loaded with
> >     BPF token; delegate_progs and delegate_attachs are meant to be used
> >     together, as full BPF program type is, in general, determined
> >     through both program type and program attach type.
> >
> > Currently, these mount options accept the following forms of values:
> >   - a special value "any", that enables all possible values of a given
> >   bit set;
> >   - numeric value (decimal or hexadecimal, determined by kernel
> >   automatically) that specifies a bit mask value directly;
> >   - all the values for a given mount option are combined, if specified
> >   multiple times. E.g., `mount -t bpf nodev /path/to/mount -o
> >   delegate_maps=0x1 -o delegate_maps=0x2` will result in a combined 0x3
> >   mask.
> >
> SNIP
> >       return 0;
> > @@ -740,10 +786,14 @@ static int populate_bpffs(struct dentry *parent)
> >  static int bpf_fill_super(struct super_block *sb, struct fs_context *fc)
> >  {
> >       static const struct tree_descr bpf_rfiles[] = { { "" } };
> > -     struct bpf_mount_opts *opts = fc->fs_private;
> > +     struct bpf_mount_opts *opts = sb->s_fs_info;
> >       struct inode *inode;
> >       int ret;
> >
> > +     /* Mounting an instance of BPF FS requires privileges */
> > +     if (fc->user_ns != &init_user_ns && !capable(CAP_SYS_ADMIN))
> > +             return -EPERM;
> > +
> >       ret = simple_fill_super(sb, BPF_FS_MAGIC, bpf_rfiles);
> >       if (ret)
> >               return ret;
> > @@ -765,7 +815,10 @@ static int bpf_get_tree(struct fs_context *fc)
> >
> >  static void bpf_free_fc(struct fs_context *fc)
> >  {
> > -     kfree(fc->fs_private);
> > +     struct bpf_mount_opts *opts = fc->s_fs_info;
> > +
> > +     if (opts)
> > +             kfree(opts);
> >  }
> >
>
> The NULL check is not needed here, use kfree(fc->s_fs_info) will be enough.

yep, dropped the check


> >  static const struct fs_context_operations bpf_context_ops = {
> > @@ -787,17 +840,32 @@ static int bpf_init_fs_context(struct fs_context *fc)
> >
> >       opts->mode = S_IRWXUGO;
> >
> > -     fc->fs_private = opts;
> > +     /* start out with no BPF token delegation enabled */
> > +     opts->delegate_cmds = 0;
> > +     opts->delegate_maps = 0;
> > +     opts->delegate_progs = 0;
> > +     opts->delegate_attachs = 0;
> > +
> > +     fc->s_fs_info = opts;
> >       fc->ops = &bpf_context_ops;
> >       return 0;
> >  }
> >
> > +static void bpf_kill_super(struct super_block *sb)
> > +{
> > +     struct bpf_mount_opts *opts = sb->s_fs_info;
> > +
> > +     kill_litter_super(sb);
> > +     kfree(opts);
> > +}
> > +
> >  static struct file_system_type bpf_fs_type = {
> >       .owner          = THIS_MODULE,
> >       .name           = "bpf",
> >       .init_fs_context = bpf_init_fs_context,
> >       .parameters     = bpf_fs_parameters,
> > -     .kill_sb        = kill_litter_super,
> > +     .kill_sb        = bpf_kill_super,
> > +     .fs_flags       = FS_USERNS_MOUNT,
> >  };
> >
> >  static int __init bpf_init(void)
>
>