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Message-Id: <20210708011833.67028-6-alexei.starovoitov@gmail.com>
Date: Wed, 7 Jul 2021 18:18:27 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: davem@...emloft.net
Cc: daniel@...earbox.net, andrii@...nel.org, netdev@...r.kernel.org,
bpf@...r.kernel.org, kernel-team@...com
Subject: [PATCH v5 bpf-next 05/11] bpf: Prevent pointer mismatch in bpf_timer_init.
From: Alexei Starovoitov <ast@...nel.org>
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@...nel.org>
---
include/linux/bpf_verifier.h | 9 ++++++++-
kernel/bpf/verifier.c | 31 ++++++++++++++++++++++++++++---
2 files changed, 36 insertions(+), 4 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index e774ecc1cd1f..5d3169b57e6e 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -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 {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e44c36107d11..cb393de3c818 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -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 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
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))
--
2.30.2
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