[PATCH 6/6] env: Add support for explicit write access list
Marek Vasut
marex at denx.de
Wed Jun 3 02:01:11 CEST 2020
This option marks any U-Boot variable which does not have explicit 'w'
writeable flag set as read-only. This way the environment can be locked
down and only variables explicitly configured to be writeable can ever
be changed by either 'env import', 'env set' or loading user environment
from environment storage.
Signed-off-by: Marek Vasut <marex at denx.de>
---
env/Kconfig | 8 ++++
env/flags.c | 92 +++++++++++++++++++++++++++++++++++++++------
include/env_flags.h | 6 ++-
lib/hashtable.c | 5 ++-
4 files changed, 98 insertions(+), 13 deletions(-)
diff --git a/env/Kconfig b/env/Kconfig
index 8166e5df91..f53a1457fb 100644
--- a/env/Kconfig
+++ b/env/Kconfig
@@ -613,6 +613,14 @@ config ENV_APPEND
with newly imported data. This may be used in combination with static
flags to e.g. to protect variables which must not be modified.
+config ENV_WRITEABLE_LIST
+ bool "Permit write access only to listed variables"
+ default n
+ help
+ If defined, only environment variables which explicitly set the 'w'
+ writeable flag can be written and modified at runtime. No variables
+ can be otherwise created, written or imported into the environment.
+
config ENV_ACCESS_IGNORE_FORCE
bool "Block forced environment operations"
default n
diff --git a/env/flags.c b/env/flags.c
index f7a53775c4..a2f6c1a3ec 100644
--- a/env/flags.c
+++ b/env/flags.c
@@ -28,8 +28,15 @@
#define ENV_FLAGS_NET_VARTYPE_REPS ""
#endif
+#if CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+#define ENV_FLAGS_WRITEABLE_VARACCESS_REPS "w"
+#else
+#define ENV_FLAGS_WRITEABLE_VARACCESS_REPS ""
+#endif
+
static const char env_flags_vartype_rep[] = "sdxb" ENV_FLAGS_NET_VARTYPE_REPS;
-static const char env_flags_varaccess_rep[] = "aroc";
+static const char env_flags_varaccess_rep[] =
+ "aroc" ENV_FLAGS_WRITEABLE_VARACCESS_REPS;
static const int env_flags_varaccess_mask[] = {
0,
ENV_FLAGS_VARACCESS_PREVENT_DELETE |
@@ -38,7 +45,11 @@ static const int env_flags_varaccess_mask[] = {
ENV_FLAGS_VARACCESS_PREVENT_DELETE |
ENV_FLAGS_VARACCESS_PREVENT_OVERWR,
ENV_FLAGS_VARACCESS_PREVENT_DELETE |
- ENV_FLAGS_VARACCESS_PREVENT_NONDEF_OVERWR};
+ ENV_FLAGS_VARACCESS_PREVENT_NONDEF_OVERWR,
+#if CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+ ENV_FLAGS_VARACCESS_WRITEABLE,
+#endif
+ };
#ifdef CONFIG_CMD_ENV_FLAGS
static const char * const env_flags_vartype_names[] = {
@@ -56,6 +67,9 @@ static const char * const env_flags_varaccess_names[] = {
"read-only",
"write-once",
"change-default",
+#if CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+ "writeable",
+#endif
};
/*
@@ -130,21 +144,33 @@ enum env_flags_vartype env_flags_parse_vartype(const char *flags)
*/
enum env_flags_varaccess env_flags_parse_varaccess(const char *flags)
{
+#if CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+ enum env_flags_varaccess va_default = env_flags_varaccess_readonly;
+#else
+ enum env_flags_varaccess va_default = env_flags_varaccess_any;
+#endif
+ enum env_flags_varaccess va;
char *access;
if (strlen(flags) <= ENV_FLAGS_VARACCESS_LOC)
- return env_flags_varaccess_any;
+ return va_default;
access = strchr(env_flags_varaccess_rep,
flags[ENV_FLAGS_VARACCESS_LOC]);
- if (access != NULL)
- return (enum env_flags_varaccess)
+ if (access != NULL) {
+ va = (enum env_flags_varaccess)
(access - &env_flags_varaccess_rep[0]);
+#if CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+ if (va != env_flags_varaccess_writeable)
+ return env_flags_varaccess_readonly;
+#endif
+ return va;
+ }
printf("## Warning: Unknown environment variable access method '%c'\n",
flags[ENV_FLAGS_VARACCESS_LOC]);
- return env_flags_varaccess_any;
+ return va_default;
}
/*
@@ -152,17 +178,29 @@ enum env_flags_varaccess env_flags_parse_varaccess(const char *flags)
*/
enum env_flags_varaccess env_flags_parse_varaccess_from_binflags(int binflags)
{
+#if CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+ enum env_flags_varaccess va_default = env_flags_varaccess_readonly;
+#else
+ enum env_flags_varaccess va_default = env_flags_varaccess_any;
+#endif
+ enum env_flags_varaccess va;
int i;
for (i = 0; i < ARRAY_SIZE(env_flags_varaccess_mask); i++)
if (env_flags_varaccess_mask[i] ==
- (binflags & ENV_FLAGS_VARACCESS_BIN_MASK))
- return (enum env_flags_varaccess)i;
+ (binflags & ENV_FLAGS_VARACCESS_BIN_MASK)) {
+ va = (enum env_flags_varaccess)i;
+#if CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+ if (va != env_flags_varaccess_writeable)
+ return env_flags_varaccess_readonly;
+#endif
+ return va;
+ }
printf("Warning: Non-standard access flags. (0x%x)\n",
binflags & ENV_FLAGS_VARACCESS_BIN_MASK);
- return env_flags_varaccess_any;
+ return va_default;
}
static inline int is_hex_prefix(const char *value)
@@ -325,14 +363,20 @@ enum env_flags_vartype env_flags_get_type(const char *name)
*/
enum env_flags_varaccess env_flags_get_varaccess(const char *name)
{
+#if CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+ const char *flags_list = NULL;
+ enum env_flags_varaccess va_default = env_flags_varaccess_readonly;
+#else
const char *flags_list = env_get(ENV_FLAGS_VAR);
+ enum env_flags_varaccess va_default = env_flags_varaccess_any;
+#endif
char flags[ENV_FLAGS_ATTR_MAX_LEN + 1];
if (env_flags_lookup(flags_list, name, flags))
- return env_flags_varaccess_any;
+ return va_default;
if (strlen(flags) <= ENV_FLAGS_VARACCESS_LOC)
- return env_flags_varaccess_any;
+ return va_default;
return env_flags_parse_varaccess(flags);
}
@@ -426,7 +470,11 @@ void env_flags_init(struct env_entry *var_entry)
int ret = 1;
if (first_call) {
+#if CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+ flags_list = ENV_FLAGS_LIST_STATIC;
+#else
flags_list = env_get(ENV_FLAGS_VAR);
+#endif
first_call = 0;
}
/* look in the ".flags" and static for a reference to this variable */
@@ -435,6 +483,16 @@ void env_flags_init(struct env_entry *var_entry)
/* if any flags were found, set the binary form to the entry */
if (!ret && strlen(flags))
var_entry->flags = env_parse_flags_to_bin(flags);
+
+#if CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+ /* Anything which is not explicitly writeable is read-only */
+ if (!(var_entry->flags & ENV_FLAGS_VARACCESS_WRITEABLE)) {
+ var_entry->flags &= ~ENV_FLAGS_VARACCESS_BIN_MASK;
+ var_entry->flags |= ENV_FLAGS_VARACCESS_PREVENT_DELETE |
+ ENV_FLAGS_VARACCESS_PREVENT_CREATE |
+ ENV_FLAGS_VARACCESS_PREVENT_OVERWR;
+ }
+#endif
}
/*
@@ -523,6 +581,18 @@ int env_flags_validate(const struct env_entry *item, const char *newval,
}
/* check for access permission */
+#if CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+ if (flag & H_DEFAULT)
+ return 0; /* Default env is always OK */
+
+ /* Writeable variables can be overwritten, anything else can not */
+ if (op == env_op_overwrite &&
+ item->flags & ENV_FLAGS_VARACCESS_WRITEABLE)
+ return 0;
+
+ return 1;
+#endif
+
#ifndef CONFIG_ENV_ACCESS_IGNORE_FORCE
if (flag & H_FORCE) {
printf("## Error: Can't force access to \"%s\"\n", name);
diff --git a/include/env_flags.h b/include/env_flags.h
index 725841a891..62c3dd9fa0 100644
--- a/include/env_flags.h
+++ b/include/env_flags.h
@@ -24,6 +24,9 @@ enum env_flags_varaccess {
env_flags_varaccess_readonly,
env_flags_varaccess_writeonce,
env_flags_varaccess_changedefault,
+#if CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+ env_flags_varaccess_writeable,
+#endif
env_flags_varaccess_end
};
@@ -173,6 +176,7 @@ int env_flags_validate(const struct env_entry *item, const char *newval,
#define ENV_FLAGS_VARACCESS_PREVENT_CREATE 0x00000010
#define ENV_FLAGS_VARACCESS_PREVENT_OVERWR 0x00000020
#define ENV_FLAGS_VARACCESS_PREVENT_NONDEF_OVERWR 0x00000040
-#define ENV_FLAGS_VARACCESS_BIN_MASK 0x00000078
+#define ENV_FLAGS_VARACCESS_WRITEABLE 0x00000080
+#define ENV_FLAGS_VARACCESS_BIN_MASK 0x000000f8
#endif /* __ENV_FLAGS_H__ */
diff --git a/lib/hashtable.c b/lib/hashtable.c
index 24aef5a085..bebad9d382 100644
--- a/lib/hashtable.c
+++ b/lib/hashtable.c
@@ -946,9 +946,12 @@ int himport_r(struct hsearch_data *htab,
e.data = value;
hsearch_r(e, ENV_ENTER, &rv, htab, flag);
- if (rv == NULL)
+#if !CONFIG_IS_ENABLED(ENV_WRITEABLE_LIST)
+ if (rv == NULL) {
printf("himport_r: can't insert \"%s=%s\" into hash table\n",
name, value);
+ }
+#endif
debug("INSERT: table %p, filled %d/%d rv %p ==> name=\"%s\" value=\"%s\"\n",
htab, htab->filled, htab->size,
--
2.25.1
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