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bpf: Update verification logic for LSM programs

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The current logic checks if the name of the BTF type passed in
attach_btf_id starts with "bpf_lsm_", this is not sufficient as it also
allows attachment to non-LSM hooks like the very function that performs
this check, i.e. bpf_lsm_verify_prog.

In order to ensure that this verification logic allows attachment to
only LSM hooks, the LSM_HOOK definitions in lsm_hook_defs.h are used to
generate a BTF_ID set. Upon verification, the attach_btf_id of the
program being attached is checked for presence in this set.

Fixes: 9e4e01dfd3 ("bpf: lsm: Implement attach, detach and execution")
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201105230651.2621917-1-kpsingh@chromium.org
This commit is contained in:
KP Singh 2020-11-05 23:06:51 +00:00 committed by Alexei Starovoitov
parent d3bec0138b
commit 6f64e47783
1 changed files with 7 additions and 3 deletions
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10
kernel/bpf/bpf_lsm.c
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@ -13,6 +13,7 @@
#include <linux/bpf_verifier.h>
#include <net/bpf_sk_storage.h>
#include <linux/bpf_local_storage.h>
#include <linux/btf_ids.h>
/* For every LSM hook that allows attachment of BPF programs, declare a nop
* function where a BPF program can be attached.
@ -26,7 +27,11 @@ noinline RET bpf_lsm_##NAME(__VA_ARGS__) \
#include <linux/lsm_hook_defs.h>
#undef LSM_HOOK
#define BPF_LSM_SYM_PREFX "bpf_lsm_"
#define LSM_HOOK(RET, DEFAULT, NAME, ...) BTF_ID(func, bpf_lsm_##NAME)
BTF_SET_START(bpf_lsm_hooks)
#include <linux/lsm_hook_defs.h>
#undef LSM_HOOK
BTF_SET_END(bpf_lsm_hooks)
int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
const struct bpf_prog *prog)
@ -37,8 +42,7 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
return -EINVAL;
}
if (strncmp(BPF_LSM_SYM_PREFX, prog->aux->attach_func_name,
sizeof(BPF_LSM_SYM_PREFX) - 1)) {
if (!btf_id_set_contains(&bpf_lsm_hooks, prog->aux->attach_btf_id)) {
bpf_log(vlog, "attach_btf_id %u points to wrong type name %s\n",
prog->aux->attach_btf_id, prog->aux->attach_func_name);
return -EINVAL;