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From 188fe5f47f9f9e8a4f67bf4e4a840ce84d80641c Mon Sep 17 00:00:00 2001
From: Jan Kiszka <jan.kiszka@siemens.com>
Date: Mon, 24 Jul 2023 08:00:34 +0200
Subject: [PATCH 5/9] Introduce validation of bgenv prior to its usage
The parsing of user variables assumes sane input so far and can be
mislead to out-of-bounds accesses, including writes. Address this by
always validating a bgenv after reading it from a partition or a file.
If an invalid bgenv is found, it is cleared to zero internally so that
the existing code will always operate against a sane state.
Include the CRC32 validation in the new helper as well which also
ensures that the checksum is tested when operating against a specific
file.
Reported by Code Intelligence.
Addresses CVE-2023-39950
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
env/env_api_fat.c | 44 ++++++++++++++++++++++++++++++++++----------
env/uservars.c | 29 +++++++++++++++++++++++++++++
include/env_api.h | 2 ++
include/uservars.h | 3 +++
tools/bg_envtools.c | 6 +++++-
5 files changed, 73 insertions(+), 11 deletions(-)
diff --git a/env/env_api_fat.c b/env/env_api_fat.c
index 0f4f474..b7540bb 100644
--- a/env/env_api_fat.c
+++ b/env/env_api_fat.c
@@ -51,6 +51,33 @@ void bgenv_be_verbose(bool v)
ebgpart_beverbose(v);
}
+static void clear_envdata(BG_ENVDATA *data)
+{
+ memset(data, 0, sizeof(BG_ENVDATA));
+ data->crc32 = crc32(0, (Bytef *)data,
+ sizeof(BG_ENVDATA) - sizeof(data->crc32));
+}
+
+bool validate_envdata(BG_ENVDATA *data)
+{
+ uint32_t sum = crc32(0, (Bytef *)data,
+ sizeof(BG_ENVDATA) - sizeof(data->crc32));
+
+ if (data->crc32 != sum) {
+ VERBOSE(stderr, "Invalid CRC32!\n");
+ /* clear invalid environment */
+ clear_envdata(data);
+ return false;
+ }
+ if (!bgenv_validate_uservars(data->userdata)) {
+ VERBOSE(stderr, "Corrupt uservars!\n");
+ /* clear invalid environment */
+ clear_envdata(data);
+ return false;
+ }
+ return true;
+}
+
bool read_env(CONFIG_PART *part, BG_ENVDATA *env)
{
if (!part) {
@@ -86,10 +113,16 @@ bool read_env(CONFIG_PART *part, BG_ENVDATA *env)
if (part->not_mounted) {
unmount_partition(part);
}
+ if (result == false) {
+ clear_envdata(env);
+ return false;
+ }
+
/* enforce NULL-termination of strings */
env->kernelfile[ENV_STRING_LENGTH - 1] = 0;
env->kernelparams[ENV_STRING_LENGTH - 1] = 0;
- return result;
+
+ return validate_envdata(env);
}
bool write_env(CONFIG_PART *part, BG_ENVDATA *env)
@@ -147,15 +180,6 @@ bool bgenv_init(void)
}
for (int i = 0; i < ENV_NUM_CONFIG_PARTS; i++) {
read_env(&config_parts[i], &envdata[i]);
- uint32_t sum = crc32(0, (Bytef *)&envdata[i],
- sizeof(BG_ENVDATA) - sizeof(envdata[i].crc32));
- if (envdata[i].crc32 != sum) {
- VERBOSE(stderr, "Invalid CRC32!\n");
- /* clear invalid environment */
- memset(&envdata[i], 0, sizeof(BG_ENVDATA));
- envdata[i].crc32 = crc32(0, (Bytef *)&envdata[i],
- sizeof(BG_ENVDATA) - sizeof(envdata[i].crc32));
- }
}
initialized = true;
return true;
diff --git a/env/uservars.c b/env/uservars.c
index f251f24..23a6920 100644
--- a/env/uservars.c
+++ b/env/uservars.c
@@ -72,6 +72,35 @@ void bgenv_map_uservar(uint8_t *udata, char **key, uint64_t *type, uint8_t **val
}
}
+bool bgenv_validate_uservars(uint8_t *udata)
+{
+ uint32_t spaceleft = ENV_MEM_USERVARS;
+
+ while (*udata) {
+ uint32_t key_len = strnlen((char *)udata, spaceleft);
+
+ /* we need space for the key string + null termination +
+ * the payload size field */
+ if (key_len + 1 + sizeof(uint32_t) >= spaceleft) {
+ return false;
+ }
+
+ spaceleft -= key_len + 1;
+ udata += key_len + 1;
+
+ uint32_t payload_size = *(uint32_t *)udata;
+
+ /* the payload must leave at least one byte free */
+ if (payload_size >= spaceleft) {
+ return false;
+ }
+
+ spaceleft -= payload_size;
+ udata += payload_size;
+ }
+ return true;
+}
+
void bgenv_serialize_uservar(uint8_t *p, char *key, uint64_t type, void *data,
uint32_t record_size)
{
diff --git a/include/env_api.h b/include/env_api.h
index b796682..02b4167 100644
--- a/include/env_api.h
+++ b/include/env_api.h
@@ -95,3 +95,5 @@ extern int bgenv_get(BGENV *env, char *key, uint64_t *type, void *data,
extern int bgenv_set(BGENV *env, char *key, uint64_t type, void *data,
uint32_t datalen);
extern uint8_t *bgenv_find_uservar(uint8_t *userdata, char *key);
+
+extern bool validate_envdata(BG_ENVDATA *data);
diff --git a/include/uservars.h b/include/uservars.h
index f2f3587..28d6502 100644
--- a/include/uservars.h
+++ b/include/uservars.h
@@ -14,6 +14,7 @@
#pragma once
+#include <stdbool.h>
#include <stdint.h>
void bgenv_map_uservar(uint8_t *udata, char **key, uint64_t *type,
@@ -35,3 +36,5 @@ uint8_t *bgenv_uservar_realloc(uint8_t *udata, uint32_t new_rsize,
uint8_t *p);
void bgenv_del_uservar(uint8_t *udata, uint8_t *var);
uint32_t bgenv_user_free(uint8_t *udata);
+
+bool bgenv_validate_uservars(uint8_t *udata);
diff --git a/tools/bg_envtools.c b/tools/bg_envtools.c
index 4d3cfa8..786d6c1 100644
--- a/tools/bg_envtools.c
+++ b/tools/bg_envtools.c
@@ -155,9 +155,13 @@ bool get_env(char *configfilepath, BG_ENVDATA *data)
"Error closing environment file after reading.\n");
};
+ if (result == false) {
+ return false;
+ }
+
/* enforce NULL-termination of strings */
data->kernelfile[ENV_STRING_LENGTH - 1] = 0;
data->kernelparams[ENV_STRING_LENGTH - 1] = 0;
- return result;
+ return validate_envdata(data);
}
--
2.40.1
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