On 11/16/20 3:01 PM, KP Singh wrote:
From: KP Singh <kpsingh@xxxxxxxxxx>
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@xxxxxxxxxx>
[...]
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
@@ -4119,6 +4128,11 @@ 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..4d04fc490a14 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 +52,23 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
return 0;
}
+BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags)
+{
This should also reject invalid flags. I'd rather change this helper from RET_VOID
to RET_INTEGER and throw -EINVAL for everything other than BPF_LSM_F_BPRM_SECUREEXEC
passed in here including zero so it can be extended in future.
+ 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_VOID,
+ .arg1_type = ARG_PTR_TO_BTF_ID,
+ .arg1_btf_id = &bpf_lsm_set_bprm_opts_btf_ids[0],
+ .arg2_type = ARG_ANYTHING,
+};
+
