Re: [PATCH bpf-next v3 1/2] bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling

On Mon, Jun 22, 2026 at 7:57 PM Alexei Starovoitov
<[email protected]> wrote:
>
> On Thu Jun 18, 2026 at 1:34 PM PDT, David Windsor wrote:
> > +
> > +static int __bpf_init_inode_xattr(struct xattr_ctx *xattr_ctx,
> > +                               const char *name__str,
> > +                               const struct bpf_dynptr *value_p)
> > +{
> > +     struct bpf_dynptr_kern *value_ptr = (struct bpf_dynptr_kern *)value_p;
> > +     size_t name_len;
> > +     void *xattr_value;
> > +     struct xattr *xattr;
> > +     struct xattr *xattrs;
> > +     int *xattr_count;
> > +     const void *value;
> > +     u32 value_len;
> > +
> > +     if (!xattr_ctx || !name__str)
> > +             return -EINVAL;
> > +
> > +     xattrs = xattr_ctx->xattrs;
> > +     xattr_count = xattr_ctx->xattr_count;
> > +     if (!xattrs || !xattr_count)
> > +             return -EINVAL;
> > +     if (bpf_xattrs_used(xattr_ctx) >= BPF_LSM_INODE_INIT_XATTRS)
> > +             return -ENOSPC;
>
> This check is good to have, but it's enough. No need to duplicate it.
> More below.
>

> > +
> >  static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)
> >  {
> >       if (!btf_id_set8_contains(&bpf_fs_kfunc_set_ids, kfunc_id) ||
> > -         prog->type == BPF_PROG_TYPE_LSM)
> > +         prog->type == BPF_PROG_TYPE_LSM) {
> > +             /* bpf_init_inode_xattr only attaches to inode_init_security. */
> > +             if (kfunc_id == bpf_init_inode_xattr_btf_ids[0] &&
> > +                 prog->aux->attach_btf_id != bpf_lsm_inode_init_security_btf_ids[0])
> > +                     return -EACCES;
>
> This is unnecessary. Only one hook will have xattr_ctx type.
> The normal verifier type enforcement will do its work.
>

Good point, thanks.

> > diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> > index 1a721fc4bef5..b41b02173e24 100644
> > --- a/kernel/bpf/trampoline.c
> > +++ b/kernel/bpf/trampoline.c
> > @@ -859,6 +859,9 @@ static int bpf_trampoline_add_prog(struct bpf_trampoline *tr,
> >       }
> >       if (cnt >= BPF_MAX_TRAMP_LINKS)
> >               return -E2BIG;
> > +     if (node->link->prog->aux->attach_limit &&
> > +         tr->progs_cnt[kind] >= node->link->prog->aux->attach_limit)
> > +             return -E2BIG;
>
> No need. The check inside kfunc is enough.
>

Paul wanted this check because it occurs at bpf prog attach time,
whereas the one in the kfunc is at inode creation time.


> >       if (!hlist_unhashed(&node->tramp_hlist))
> >               /* prog already linked */
> >               return -EBUSY;
> > diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
> > index 40efde233f3a..d7c44c5c0e30 100644
> > --- a/security/bpf/hooks.c
> > +++ b/security/bpf/hooks.c
> > @@ -30,6 +30,7 @@ static int __init bpf_lsm_init(void)
> >
> >  struct lsm_blob_sizes bpf_lsm_blob_sizes __ro_after_init = {
> >       .lbs_inode = sizeof(struct bpf_storage_blob),
> > +     .lbs_xattr_count = BPF_LSM_INODE_INIT_XATTRS,
> >  };
> >
> >  DEFINE_LSM(bpf) = {
> > diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
> > index b59e3f121b8a..e0a05162accc 100644
> > --- a/security/integrity/evm/evm_main.c
> > +++ b/security/integrity/evm/evm_main.c
> > @@ -1062,14 +1062,16 @@ static int evm_inode_copy_up_xattr(struct dentry *src, const char *name)
> >   * evm_inode_init_security - initializes security.evm HMAC value
> >   */
> >  int evm_inode_init_security(struct inode *inode, struct inode *dir,
> > -                         const struct qstr *qstr, struct xattr *xattrs,
> > -                         int *xattr_count)
> > +                         const struct qstr *qstr,
> > +                         struct xattr_ctx *xattr_ctx)
>
> the rest looks good.
> Pls split the patch. Introduce xattr_ctx first across the LSMs.
> Then another patch with a new kfunc.
>
> pw-bot: cr