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.
> 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)
