On Jul 7, 2026 David Windsor <[email protected]> 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 <[email protected]> > Signed-off-by: David Windsor <[email protected]> > --- > fs/bpf_fs_kfuncs.c | 36 ++++++++++++++++++++++++++++++++++++ > 1 file changed, 36 insertions(+) > > diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c > index 768aca2dc0f0..ad0025f2264a 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(); > > @@ -374,6 +376,39 @@ __bpf_kfunc struct inode *bpf_real_inode(struct dentry > *dentry) > return d_real_inode(dentry); > } > > +/** > + * 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, negative error on failure. > + */ > +__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; > + > + 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, value, > + value_len); > +}
I'm sorry David, now that I'm seeing this function again, especially with the LSM specific bits extracted into a LSM function, this absolutely belongs somewhere under security/. It's only callable from within a BPF LSM callback and all it does outside of some BPF pointer boilerplate is call right back into a LSM helper function. If the BPF maintainers aren't willing to accept that, then we will all need to find another way. > __bpf_kfunc_end_defs(); > > BTF_KFUNCS_START(bpf_fs_kfunc_set_ids) > @@ -385,6 +420,7 @@ 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_inode, KF_SLEEPABLE | KF_RET_NULL) > +BTF_ID_FLAGS(func, bpf_init_inode_xattr) > BTF_KFUNCS_END(bpf_fs_kfunc_set_ids) > > static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id) > -- > 2.53.0 -- paul-moore.com
