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libbpf: Don't take direct pointers into BTF data from st_ops

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In struct bpf_struct_ops, we have take a pointer to a BTF type name, and
a struct btf_type. This was presumably done for convenience, but can
actually result in subtle and confusing bugs given that BTF data can be
invalidated before a program is loaded. For example, in sched_ext, we
may sometimes resize a data section after a skeleton has been opened,
but before the struct_ops scheduler map has been loaded. This may cause
the BTF data to be realloc'd, which can then cause a UAF when loading
the program because the struct_ops map has pointers directly into the
BTF data.

We're already storing the BTF type_id in struct bpf_struct_ops. Because
type_id is stable, we can therefore just update the places where we were
looking at those pointers to instead do the lookups we need from the
type_id.

Fixes: 590a008882 ("bpf: libbpf: Add STRUCT_OPS support")
Signed-off-by: David Vernet <void@manifault.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240724171459.281234-1-void@manifault.com
This commit is contained in:
David Vernet 2024-07-24 12:14:58 -05:00 committed by Andrii Nakryiko
parent 8efffab4e5
commit 04a94133f1
1 changed files with 13 additions and 10 deletions
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23
tools/lib/bpf/libbpf.c
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@ -496,8 +496,6 @@ struct bpf_program {
};
struct bpf_struct_ops {
const char *tname;
const struct btf_type *type;
struct bpf_program **progs;
__u32 *kern_func_off;
/* e.g. struct tcp_congestion_ops in bpf_prog's btf format */
@ -1083,11 +1081,14 @@ static int bpf_object_adjust_struct_ops_autoload(struct bpf_object *obj)
continue;
for (j = 0; j < obj->nr_maps; ++j) {
const struct btf_type *type;
map = &obj->maps[j];
if (!bpf_map__is_struct_ops(map))
continue;
vlen = btf_vlen(map->st_ops->type);
type = btf__type_by_id(obj->btf, map->st_ops->type_id);
vlen = btf_vlen(type);
for (k = 0; k < vlen; ++k) {
slot_prog = map->st_ops->progs[k];
if (prog != slot_prog)
@ -1121,8 +1122,8 @@ static int bpf_map__init_kern_struct_ops(struct bpf_map *map)
int err;
st_ops = map->st_ops;
type = st_ops->type;
tname = st_ops->tname;
type = btf__type_by_id(btf, st_ops->type_id);
tname = btf__name_by_offset(btf, type->name_off);
err = find_struct_ops_kern_types(obj, tname, &mod_btf,
&kern_type, &kern_type_id,
&kern_vtype, &kern_vtype_id,
@ -1423,8 +1424,6 @@ static int init_struct_ops_maps(struct bpf_object *obj, const char *sec_name,
memcpy(st_ops->data,
data->d_buf + vsi->offset,
type->size);
st_ops->tname = tname;
st_ops->type = type;
st_ops->type_id = type_id;
pr_debug("struct_ops init: struct %s(type_id=%u) %s found at offset %u\n",
@ -8445,11 +8444,13 @@ static int bpf_object__resolve_externs(struct bpf_object *obj,
static void bpf_map_prepare_vdata(const struct bpf_map *map)
{
const struct btf_type *type;
struct bpf_struct_ops *st_ops;
__u32 i;
st_ops = map->st_ops;
for (i = 0; i < btf_vlen(st_ops->type); i++) {
type = btf__type_by_id(map->obj->btf, st_ops->type_id);
for (i = 0; i < btf_vlen(type); i++) {
struct bpf_program *prog = st_ops->progs[i];
void *kern_data;
int prog_fd;
@ -9712,6 +9713,7 @@ static struct bpf_map *find_struct_ops_map_by_offset(struct bpf_object *obj,
static int bpf_object__collect_st_ops_relos(struct bpf_object *obj,
Elf64_Shdr *shdr, Elf_Data *data)
{
const struct btf_type *type;
const struct btf_member *member;
struct bpf_struct_ops *st_ops;
struct bpf_program *prog;
@ -9771,13 +9773,14 @@ static int bpf_object__collect_st_ops_relos(struct bpf_object *obj,
}
insn_idx = sym->st_value / BPF_INSN_SZ;
member = find_member_by_offset(st_ops->type, moff * 8);
type = btf__type_by_id(btf, st_ops->type_id);
member = find_member_by_offset(type, moff * 8);
if (!member) {
pr_warn("struct_ops reloc %s: cannot find member at moff %u\n",
map->name, moff);
return -EINVAL;
}
member_idx = member - btf_members(st_ops->type);
member_idx = member - btf_members(type);
name = btf__name_by_offset(btf, member->name_off);
if (!resolve_func_ptr(btf, member->type, NULL)) {