[PATCH v6 bpf-next 3/4] bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling

[Paul Moore]

On Thu, Jul 30, 2026 at 7:45 PM David Windsor <dwindsor at gmail.com> wrote:
>
> Add bpf_init_inode_xattr() kfunc for BPF LSM programs to atomically set
> xattrs via the inode_init_security hook using security_lsmxattr_add().
> The hook now passes its xattr state as a single struct lsm_xattrs
> object, which the kfunc takes directly.
>
> This kfunc is only callable from inode_init_security; the verifier
> rejects attempts to call it elsewhere.
>
> A previous attempt [1] required a kmalloc string output protocol for
> the xattr name. Since commit 6bcdfd2cac55 ("security: Allow all LSMs to
> provide xattrs for inode_init_security hook") [2], the xattr name is no
> longer allocated; it is a static constant.
>
> Link: https://kernsec.org/pipermail/linux-security-module-archive/2022-October/034878.html [1]
> Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6bcdfd2cac55 [2]
> Suggested-by: Song Liu <song at kernel.org>
> Signed-off-by: David Windsor <dwindsor at gmail.com>
> ---
>  fs/bpf_fs_kfuncs.c | 41 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 41 insertions(+)
>
> diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
> index f1863a891db6..7b55073934e0 100644
> --- a/fs/bpf_fs_kfuncs.c
> +++ b/fs/bpf_fs_kfuncs.c
> @@ -11,7 +11,9 @@
>  #include <linux/file.h>
>  #include <linux/kernfs.h>
>  #include <linux/mm.h>
> +#include <linux/security.h>
>  #include <linux/xattr.h>
> +#include <uapi/linux/lsm.h>
>
>  __bpf_kfunc_start_defs();
>
> @@ -379,6 +381,44 @@ __bpf_kfunc struct inode *bpf_real_data_inode(struct file *file)
>         return d_real_inode(file_dentry(file));
>  }
>
> +/**
> + * bpf_init_inode_xattr - set an xattr on a new inode from inode_init_security
> + * @xattrs: inode_init_security xattr state from the hook context
> + * @name__str: xattr name (e.g., "bpf.file_label")
> + * @value_p: dynptr containing the xattr value
> + *
> + * Only callable from lsm/inode_init_security programs.
> + *
> + * Return: 0 on success, -EOPNOTSUPP if the filesystem does not accept
> + *         xattrs at inode creation, negative error on other failures.
> + */
> +__bpf_kfunc int bpf_init_inode_xattr(struct lsm_xattrs *xattrs,
> +                                    const char *name__str,
> +                                    const struct bpf_dynptr *value_p)
> +{
> +       struct bpf_dynptr_kern *value_ptr = (struct bpf_dynptr_kern *)value_p;
> +       const void *value;
> +       u32 value_len;
> +
> +       if (!name__str)
> +               return -EINVAL;
> +       if (strncmp(name__str, XATTR_BPF_LSM_SUFFIX,
> +                   sizeof(XATTR_BPF_LSM_SUFFIX) - 1))
> +               return -EPERM;
> +
> +       if (!xattrs->xattrs)
> +               return -EOPNOTSUPP;
> +
> +       value_len = __bpf_dynptr_size(value_ptr);
> +       value = __bpf_dynptr_data(value_ptr, value_len);
> +       if (!value)
> +               return -EINVAL;
> +
> +       return security_lsmxattr_add(xattrs, LSM_ID_BPF,
> +                                    name__str + sizeof(XATTR_BPF_LSM_SUFFIX) - 1,
> +                                    value, value_len);
> +}
> +

Based on our discussion in the v5 patchset, I was expecting to see
this under security/; did something happen, or was there some
confusion?

-- 
paul-moore.com