Messages in this thread | | | Subject | Re: [PATCH bpf-next v3 1/2] bpf: Add bpf_lsm_set_bprm_opts helper | From | Daniel Borkmann <> | Date | Tue, 17 Nov 2020 23:41:43 +0100 |
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On 11/17/20 3:13 AM, KP Singh wrote: > From: KP Singh <kpsingh@google.com> > > The helper allows modification of certain bits on the linux_binprm > struct starting with the secureexec bit which can be updated using the > BPF_LSM_F_BPRM_SECUREEXEC flag. > > secureexec can be set by the LSM for privilege gaining executions to set > the AT_SECURE auxv for glibc. When set, the dynamic linker disables the > use of certain environment variables (like LD_PRELOAD). > > Signed-off-by: KP Singh <kpsingh@google.com> > --- > include/uapi/linux/bpf.h | 18 ++++++++++++++++++ > kernel/bpf/bpf_lsm.c | 27 +++++++++++++++++++++++++++ > scripts/bpf_helpers_doc.py | 2 ++ > tools/include/uapi/linux/bpf.h | 18 ++++++++++++++++++ > 4 files changed, 65 insertions(+) > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > index 162999b12790..bfa79054d106 100644 > --- a/include/uapi/linux/bpf.h > +++ b/include/uapi/linux/bpf.h > @@ -3787,6 +3787,18 @@ union bpf_attr { > * *ARG_PTR_TO_BTF_ID* of type *task_struct*. > * Return > * Pointer to the current task. > + * > + * long bpf_lsm_set_bprm_opts(struct linux_binprm *bprm, u64 flags) > + *
small nit: should have no extra newline (same for the tools/ copy)
> + * Description > + * Set or clear certain options on *bprm*: > + * > + * **BPF_LSM_F_BPRM_SECUREEXEC** Set the secureexec bit > + * which sets the **AT_SECURE** auxv for glibc. The bit > + * is cleared if the flag is not specified. > + * Return > + * **-EINVAL** if invalid *flags* are passed. > + * > */ > #define __BPF_FUNC_MAPPER(FN) \ > FN(unspec), \ > @@ -3948,6 +3960,7 @@ union bpf_attr { > FN(task_storage_get), \ > FN(task_storage_delete), \ > FN(get_current_task_btf), \ > + FN(lsm_set_bprm_opts), \ > /* */ > > /* integer value in 'imm' field of BPF_CALL instruction selects which helper > @@ -4119,6 +4132,11 @@ enum bpf_lwt_encap_mode { > BPF_LWT_ENCAP_IP, > }; > > +/* Flags for LSM helpers */ > +enum { > + BPF_LSM_F_BPRM_SECUREEXEC = (1ULL << 0), > +}; > + > #define __bpf_md_ptr(type, name) \ > union { \ > type name; \ > diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c > index 553107f4706a..cd85482228a0 100644 > --- a/kernel/bpf/bpf_lsm.c > +++ b/kernel/bpf/bpf_lsm.c > @@ -7,6 +7,7 @@ > #include <linux/filter.h> > #include <linux/bpf.h> > #include <linux/btf.h> > +#include <linux/binfmts.h> > #include <linux/lsm_hooks.h> > #include <linux/bpf_lsm.h> > #include <linux/kallsyms.h> > @@ -51,6 +52,30 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, > return 0; > } > > +/* Mask for all the currently supported BPRM option flags */ > +#define BPF_LSM_F_BRPM_OPTS_MASK BPF_LSM_F_BPRM_SECUREEXEC > + > +BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags) > +{ > +
ditto
Would have fixed up these things on the fly while applying, but one small item I wanted to bring up here given uapi which will then freeze: it would be cleaner to call the helper just bpf_bprm_opts_set() or so given it's implied that we attach to lsm here and we don't use _lsm in the naming for the others either. Similarly, I'd drop the _LSM from the flag/mask.
> + if (flags & ~BPF_LSM_F_BRPM_OPTS_MASK) > + return -EINVAL; > + > + bprm->secureexec = (flags & BPF_LSM_F_BPRM_SECUREEXEC); > + return 0; > +} > + > +BTF_ID_LIST_SINGLE(bpf_lsm_set_bprm_opts_btf_ids, struct, linux_binprm) > + > +const static struct bpf_func_proto bpf_lsm_set_bprm_opts_proto = { > + .func = bpf_lsm_set_bprm_opts, > + .gpl_only = false, > + .ret_type = RET_INTEGER, > + .arg1_type = ARG_PTR_TO_BTF_ID, > + .arg1_btf_id = &bpf_lsm_set_bprm_opts_btf_ids[0], > + .arg2_type = ARG_ANYTHING, > +}; > + > static const struct bpf_func_proto * > bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) > { > @@ -71,6 +96,8 @@ bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) > return &bpf_task_storage_get_proto; > case BPF_FUNC_task_storage_delete: > return &bpf_task_storage_delete_proto; > + case BPF_FUNC_lsm_set_bprm_opts: > + return &bpf_lsm_set_bprm_opts_proto; > default: > return tracing_prog_func_proto(func_id, prog); > }
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