From: Christian Brauner <[email protected]> The fs kfuncs are currently exclusive to LSM programs. A binfmt_misc load program needs a subset of them to do anything interesting: to compute an interpreter relative to the binary's location it wants bpf_path_d_path() on bprm->file->f_path, and matching on per-binary metadata wants bpf_get_file_xattr() and friends.
Register the fs kfunc set for struct_ops programs as well and extend the filter to admit binfmt_misc_ops programs. The xattr setters stay exclusive to LSM programs: a binary type handler decides how to run a binary, it has no business modifying filesystem state. This only takes effect in builds that have the fs kfunc set at all, i.e. CONFIG_BPF_LSM. Without it a binfmt_misc handler is limited to bprm fields and the file-backed dynptr, which are provided by the common kfunc set. Link: https://lore.kernel.org/[email protected] Signed-off-by: Christian Brauner (Amutable) <[email protected]> --- fs/bpf_fs_kfuncs.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c index 768aca2dc..aa1fe988b 100644 --- a/fs/bpf_fs_kfuncs.c +++ b/fs/bpf_fs_kfuncs.c @@ -1,6 +1,7 @@ // SPDX-License-Identifier: GPL-2.0 /* Copyright (c) 2024 Google LLC. */ +#include <linux/binfmt_misc.h> #include <linux/bpf.h> #include <linux/bpf_lsm.h> #include <linux/btf.h> @@ -387,10 +388,20 @@ BTF_ID_FLAGS(func, bpf_remove_dentry_xattr, KF_SLEEPABLE) BTF_ID_FLAGS(func, bpf_real_inode, KF_SLEEPABLE | KF_RET_NULL) BTF_KFUNCS_END(bpf_fs_kfunc_set_ids) +/* Side-effecting kfuncs that stay exclusive to LSM programs. */ +BTF_SET_START(bpf_fs_kfunc_lsm_only_ids) +BTF_ID(func, bpf_set_dentry_xattr) +BTF_ID(func, bpf_remove_dentry_xattr) +BTF_SET_END(bpf_fs_kfunc_lsm_only_ids) + 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) + if (!btf_id_set8_contains(&bpf_fs_kfunc_set_ids, kfunc_id)) + return 0; + if (prog->type == BPF_PROG_TYPE_LSM) + return 0; + if (bpf_prog_is_binfmt_misc_ops(prog) && + !btf_id_set_contains(&bpf_fs_kfunc_lsm_only_ids, kfunc_id)) return 0; return -EACCES; } @@ -433,7 +444,13 @@ static const struct btf_kfunc_id_set bpf_fs_kfunc_set = { static int __init bpf_fs_kfuncs_init(void) { - return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fs_kfunc_set); + int ret; + + ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fs_kfunc_set); + if (ret || !IS_ENABLED(CONFIG_BINFMT_MISC_BPF)) + return ret; + return register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, + &bpf_fs_kfunc_set); } late_initcall(bpf_fs_kfuncs_init); -- 2.51.2
