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

> 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)

Paul Moore raised a concern about the location of this kfunc. As the LSM
maintainer, he stated that this kfunc must be placed in
security/bpf_lsm_kfuncs.c to be acceptable.

In the v6 discussion, he explained: "The new LSM kfunc must go in
security/bpf_lsm_kfuncs.c; if that isn't acceptable to the BPF developers
then David will need to find a new way that doesn't involve kfuncs."

Kumar Kartikeya Dwivedi disagreed with this placement requirement, arguing
that it should remain in fs/ with other kfuncs. This represents an
unresolved maintainer disagreement.

Should this kfunc be moved to security/bpf_lsm_kfuncs.c as the LSM
maintainer requested, or does this need further discussion between the BPF
and LSM maintainers before merging?

Reference: https://lore.kernel.org/all/CAHC9VhTS7rSnBqg00ZxNkcZyh_=EeJmn_4z3CTCCxreEEDtTtg@mail.gmail.com/

> +{
> +	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);
> +}
> +
>  __bpf_kfunc_end_defs();
>
>  BTF_KFUNCS_START(bpf_fs_kfunc_set_ids)
> @@ -390,6 +430,7 @@ BTF_ID_FLAGS(func, bpf_get_file_xattr, KF_SLEEPABLE)
>  BTF_ID_FLAGS(func, bpf_set_dentry_xattr, KF_SLEEPABLE)
>  BTF_ID_FLAGS(func, bpf_remove_dentry_xattr, KF_SLEEPABLE)
>  BTF_ID_FLAGS(func, bpf_real_data_inode, KF_SLEEPABLE | KF_RET_NULL)
> +BTF_ID_FLAGS(func, bpf_init_inode_xattr)
>  BTF_KFUNCS_END(bpf_fs_kfunc_set_ids)


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/30592505811