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bpf: Prevent pointer mismatch in bpf_timer_init.

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bpf_timer_init() arguments are:
1. pointer to a timer (which is embedded in map element).
2. pointer to a map.
Make sure that pointer to a timer actually belongs to that map.

Use map_uid (which is unique id of inner map) to reject:
inner_map1 = bpf_map_lookup_elem(outer_map, key1)
inner_map2 = bpf_map_lookup_elem(outer_map, key2)
if (inner_map1 && inner_map2) {
    timer = bpf_map_lookup_elem(inner_map1);
    if (timer)
        // mismatch would have been allowed
        bpf_timer_init(timer, inner_map2);
}

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210715005417.78572-6-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2021-07-14 17:54:11 -07:00 committed by Daniel Borkmann
parent 68134668c1
commit 3e8ce29850
2 changed files with 36 additions and 4 deletions
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9
include/linux/bpf_verifier.h
View File

@ -53,7 +53,14 @@ struct bpf_reg_state {
/* valid when type == CONST_PTR_TO_MAP | PTR_TO_MAP_VALUE |
* PTR_TO_MAP_VALUE_OR_NULL
*/
struct bpf_map *map_ptr;
struct {
struct bpf_map *map_ptr;
/* To distinguish map lookups from outer map
* the map_uid is non-zero for registers
* pointing to inner maps.
*/
u32 map_uid;
};
/* for PTR_TO_BTF_ID */
struct {

31
kernel/bpf/verifier.c
View File

@ -255,6 +255,7 @@ struct bpf_call_arg_meta {
int mem_size;
u64 msize_max_value;
int ref_obj_id;
int map_uid;
int func_id;
struct btf *btf;
u32 btf_id;
@ -1135,6 +1136,10 @@ static void mark_ptr_not_null_reg(struct bpf_reg_state *reg)
if (map->inner_map_meta) {
reg->type = CONST_PTR_TO_MAP;
reg->map_ptr = map->inner_map_meta;
/* transfer reg's id which is unique for every map_lookup_elem
* as UID of the inner map.
*/
reg->map_uid = reg->id;
} else if (map->map_type == BPF_MAP_TYPE_XSKMAP) {
reg->type = PTR_TO_XDP_SOCK;
} else if (map->map_type == BPF_MAP_TYPE_SOCKMAP ||
@ -4708,6 +4713,7 @@ static int process_timer_func(struct bpf_verifier_env *env, int regno,
verbose(env, "verifier bug. Two map pointers in a timer helper\n");
return -EFAULT;
}
meta->map_uid = reg->map_uid;
meta->map_ptr = map;
return 0;
}
@ -5006,11 +5012,29 @@ skip_type_check:
if (arg_type == ARG_CONST_MAP_PTR) {
/* bpf_map_xxx(map_ptr) call: remember that map_ptr */
if (meta->map_ptr && meta->map_ptr != reg->map_ptr) {
verbose(env, "Map pointer doesn't match bpf_timer.\n");
return -EINVAL;
if (meta->map_ptr) {
/* Use map_uid (which is unique id of inner map) to reject:
* inner_map1 = bpf_map_lookup_elem(outer_map, key1)
* inner_map2 = bpf_map_lookup_elem(outer_map, key2)
* if (inner_map1 && inner_map2) {
* timer = bpf_map_lookup_elem(inner_map1);
* if (timer)
* // mismatch would have been allowed
* bpf_timer_init(timer, inner_map2);
* }
*
* Comparing map_ptr is enough to distinguish normal and outer maps.
*/
if (meta->map_ptr != reg->map_ptr ||
meta->map_uid != reg->map_uid) {
verbose(env,
"timer pointer in R1 map_uid=%d doesn't match map pointer in R2 map_uid=%d\n",
meta->map_uid, reg->map_uid);
return -EINVAL;
}
}
meta->map_ptr = reg->map_ptr;
meta->map_uid = reg->map_uid;
} else if (arg_type == ARG_PTR_TO_MAP_KEY) {
/* bpf_map_xxx(..., map_ptr, ..., key) call:
* check that [key, key + map->key_size) are within
@ -6204,6 +6228,7 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
return -EINVAL;
}
regs[BPF_REG_0].map_ptr = meta.map_ptr;
regs[BPF_REG_0].map_uid = meta.map_uid;
if (fn->ret_type == RET_PTR_TO_MAP_VALUE) {
regs[BPF_REG_0].type = PTR_TO_MAP_VALUE;
if (map_value_has_spin_lock(meta.map_ptr))