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bpf: Fix oob access in cgroup local storage

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Lonial reported that an out-of-bounds access in cgroup local storage
can be crafted via tail calls. Given two programs each utilizing a
cgroup local storage with a different value size, and one program
doing a tail call into the other. The verifier will validate each of
the indivial programs just fine. However, in the runtime context
the bpf_cg_run_ctx holds an bpf_prog_array_item which contains the
BPF program as well as any cgroup local storage flavor the program
uses. Helpers such as bpf_get_local_storage() pick this up from the
runtime context:

  ctx = container_of(current->bpf_ctx, struct bpf_cg_run_ctx, run_ctx);
  storage = ctx->prog_item->cgroup_storage[stype];

  if (stype == BPF_CGROUP_STORAGE_SHARED)
    ptr = &READ_ONCE(storage->buf)->data[0];
  else
    ptr = this_cpu_ptr(storage->percpu_buf);

For the second program which was called from the originally attached
one, this means bpf_get_local_storage() will pick up the former
program's map, not its own. With mismatching sizes, this can result
in an unintended out-of-bounds access.

To fix this issue, we need to extend bpf_map_owner with an array of
storage_cookie[] to match on i) the exact maps from the original
program if the second program was using bpf_get_local_storage(), or
ii) allow the tail call combination if the second program was not
using any of the cgroup local storage maps.

Fixes: 7d9c342789 ("bpf: Make cgroup storages shared between programs on the same cgroup")
Reported-by: Lonial Con <kongln9170@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20250730234733.530041-4-daniel@iogearbox.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2025-07-31 01:47:33 +02:00 committed by Alexei Starovoitov
parent 9621e60f59
commit abad3d0bad
2 changed files with 16 additions and 0 deletions
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1
include/linux/bpf.h
View File

@ -283,6 +283,7 @@ struct bpf_map_owner {
enum bpf_prog_type type;
bool jited;
bool xdp_has_frags;
u64 storage_cookie[MAX_BPF_CGROUP_STORAGE_TYPE];
const struct btf_type *attach_func_proto;
};

15
kernel/bpf/core.c
View File

@ -2378,7 +2378,9 @@ static bool __bpf_prog_map_compatible(struct bpf_map *map,
{
enum bpf_prog_type prog_type = resolve_prog_type(fp);
struct bpf_prog_aux *aux = fp->aux;
enum bpf_cgroup_storage_type i;
bool ret = false;
u64 cookie;
if (fp->kprobe_override)
return ret;
@ -2393,11 +2395,24 @@ static bool __bpf_prog_map_compatible(struct bpf_map *map,
map->owner->jited = fp->jited;
map->owner->xdp_has_frags = aux->xdp_has_frags;
map->owner->attach_func_proto = aux->attach_func_proto;
for_each_cgroup_storage_type(i) {
map->owner->storage_cookie[i] =
aux->cgroup_storage[i] ?
aux->cgroup_storage[i]->cookie : 0;
}
ret = true;
} else {
ret = map->owner->type == prog_type &&
map->owner->jited == fp->jited &&
map->owner->xdp_has_frags == aux->xdp_has_frags;
for_each_cgroup_storage_type(i) {
if (!ret)
break;
cookie = aux->cgroup_storage[i] ?
aux->cgroup_storage[i]->cookie : 0;
ret = map->owner->storage_cookie[i] == cookie ||
!cookie;
}
if (ret &&
map->owner->attach_func_proto != aux->attach_func_proto) {
switch (prog_type) {