On Tue, Oct 20, 2015 at 10:39:12AM +0200, Marc Kleine-Budde wrote:
> This patch adds hmac support to the raw backend.
>
> With this patch, modifications of the header or data of a state partition can
> be detected, as the hmac woudln't match anymore. The hmac relies on a shared
> secret, which is requested from the keystore, with keystore_get_secret() using
> the name of the state partition as the "name" of the secret.
>
> Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
> ---
> common/state.c | 117 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 109 insertions(+), 8 deletions(-)
>
> diff --git a/common/state.c b/common/state.c
> index d37f4ab4b539..234b4c01244c 100644
> --- a/common/state.c
> +++ b/common/state.c
> @@ -15,6 +15,7 @@
> */
>
> #include <common.h>
> +#include <digest.h>
> #include <environment.h>
> #include <errno.h>
> #include <fcntl.h>
> @@ -28,6 +29,8 @@
> #include <state.h>
> #include <xfuncs.h>
>
> +#include <crypto/keystore.h>
> +
> #include <linux/mtd/mtd-abi.h>
> #include <linux/mtd/mtd.h>
> #include <linux/list.h>
> @@ -41,7 +44,7 @@ struct state_backend;
>
> struct state {
> struct device_d dev;
> - const struct device_node *root;
> + struct device_node *root;
> struct list_head variables;
> const char *name;
> struct list_head list;
> @@ -55,6 +58,7 @@ struct state_backend {
> const char *name;
> const char *of_path;
> const char *path;
> + struct digest *digest;
> };
>
> enum state_variable_type {
> @@ -948,6 +952,16 @@ static int of_state_fixup(struct device_node *root, void *ctx)
> if (ret)
> goto out;
>
> + if (state->backend->digest) {
> + p = of_new_property(new_node, "algo",
> + digest_name(state->backend->digest),
> + strlen(digest_name(state->backend->digest)) + 1);
> + if (!p) {
> + ret = -ENOMEM;
> + goto out;
> + }
> + }
> +
> /* address-cells + size-cells */
> ret = of_property_write_u32(new_node, "#address-cells", 1);
> if (ret)
> @@ -1230,7 +1244,7 @@ int state_backend_dtb_file(struct state *state, const char *of_path, const char
> struct state_backend_raw {
> struct state_backend backend;
> unsigned long size_data; /* The raw data size (without header) */
> - unsigned long size_full; /* The size header + raw data */
> + unsigned long size_full; /* The size header + raw data + hmac */
> unsigned long stride; /* The stride size in bytes of the copies */
> off_t offset; /* offset in the storage file */
> size_t size; /* size of the storage area */
> @@ -1253,8 +1267,9 @@ static int backend_raw_load_one(struct state_backend_raw *backend_raw,
> struct state_variable *sv;
> struct backend_raw_header header = {};
> unsigned long max_len;
> + int d_len = 0;
> int ret;
> - void *buf, *data;
> + void *buf, *data, *hmac;
>
> max_len = backend_raw->stride;
>
> @@ -1285,6 +1300,11 @@ static int backend_raw_load_one(struct state_backend_raw *backend_raw,
> return -EINVAL;
> }
>
> + if (backend_raw->backend.digest) {
> + d_len = digest_length(backend_raw->backend.digest);
> + max_len -= d_len;
> + }
> +
> if (header.data_len > max_len) {
> dev_err(&state->dev,
> "invalid data_len %u in header, max is %lu\n",
> @@ -1292,14 +1312,15 @@ static int backend_raw_load_one(struct state_backend_raw *backend_raw,
> return -EINVAL;
> }
>
> - buf = xzalloc(sizeof(header) + header.data_len);
> + buf = xzalloc(sizeof(header) + header.data_len + d_len);
> data = buf + sizeof(header);
> + hmac = data + header.data_len;
>
> ret = lseek(fd, offset, SEEK_SET);
> if (ret < 0)
> goto out_free;
>
> - ret = read_full(fd, buf, sizeof(header) + header.data_len);
> + ret = read_full(fd, buf, sizeof(header) + header.data_len + d_len);
> if (ret < 0)
> goto out_free;
>
> @@ -1312,6 +1333,23 @@ static int backend_raw_load_one(struct state_backend_raw *backend_raw,
> goto out_free;
> }
>
> + if (backend_raw->backend.digest) {
> + struct digest *d = backend_raw->backend.digest;
> +
> + ret = digest_init(d);
> + if (ret)
> + goto out_free;
> +
> + /* hmac over header and data */
> + ret = digest_update(d, buf, sizeof(header) + header.data_len);
> + if (ret)
> + goto out_free;
> +
> + ret = digest_verify(d, hmac);
> + if (ret < 0)
> + goto out_free;
> + }
> +
> list_for_each_entry(sv, &state->variables, list) {
> if (sv->start + sv->size > header.data_len)
> break;
> @@ -1392,7 +1430,7 @@ static int state_backend_raw_save(struct state_backend *backend,
> struct state_backend_raw *backend_raw = container_of(backend,
> struct state_backend_raw, backend);
> int ret = 0, fd, i;
> - void *buf, *data;
> + void *buf, *data, *hmac;
> struct backend_raw_header *header;
> struct state_variable *sv;
>
> @@ -1400,6 +1438,7 @@ static int state_backend_raw_save(struct state_backend *backend,
>
> header = buf;
> data = buf + sizeof(*header);
> + hmac = data + backend_raw->size_data;
>
> list_for_each_entry(sv, &state->variables, list)
> memcpy(data + sv->start, sv->raw, sv->size);
> @@ -1410,6 +1449,23 @@ static int state_backend_raw_save(struct state_backend *backend,
> header->header_crc = crc32(0, header,
> sizeof(*header) - sizeof(uint32_t));
>
> + if (backend_raw->backend.digest) {
> + struct digest *d = backend_raw->backend.digest;
> +
> + ret = digest_init(d);
> + if (ret)
> + goto out_free;
> +
> + /* hmac over header and data */
> + ret = digest_update(d, buf, sizeof(*header) + backend_raw->size_data);
> + if (ret)
> + goto out_free;
> +
> + ret = digest_final(d, hmac);
> + if (ret < 0)
> + goto out_free;
> + }
> +
> fd = open(backend->path, O_WRONLY);
> if (fd < 0)
> goto out_free;
> @@ -1494,6 +1550,43 @@ static int state_backend_raw_file_get_size(const char *path, size_t *out_size)
> return ret;
> }
>
> +static int state_backend_raw_file_init_digest(struct state *state, struct state_backend_raw *backend_raw)
> +{
> + struct digest *digest;
> + const char *algo;
> + const unsigned char *key;
> + int key_len, ret;
> +
> + ret = of_property_read_string(state->root, "algo", &algo);
This needs an update to Documentation/devicetree/bindings/barebox/barebox,state.rst
> + if (ret == -EINVAL) /* -EINVAL == does not exist */
> + return 0;
-EINVAL is such a widespread error value. Maybe better explicitly test
for existence with of_find_property?
> + else if (ret)
> + return ret;
> +
> + ret = keystore_get_secret(state->name, &key, &key_len);
> + if (ret == -ENOENT) /* -ENOENT == does not exist */
> + return -EPROBE_DEFER;
> + else if (ret)
> + return ret;
> +
> + digest = digest_alloc(algo);
> + if (!digest) {
> + dev_info(&state->dev, "algo %s not found - probe deferred\n", algo);
> + return -EPROBE_DEFER;
> + }
> +
> + ret = digest_set_key(digest, key, key_len);
> + if (ret) {
> + digest_free(digest);
> + return ret;
> + }
> +
> + backend_raw->backend.digest = digest;
> + backend_raw->size_full = digest_length(digest);
> +
> + return 0;
> +}
> +
> /*
> * state_backend_raw_file - create a raw file backend store for a state instance
> *
> @@ -1534,8 +1627,14 @@ int state_backend_raw_file(struct state *state, const char *of_path,
> return -EINVAL;
>
> backend_raw = xzalloc(sizeof(*backend_raw));
> - backend = &backend_raw->backend;
>
> + ret = state_backend_raw_file_init_digest(state, backend_raw);
> + if (ret) {
> + free(backend_raw);
> + return ret;
> + }
Maybe better make this configurable with correct dependencies
(CONFIG_CRYPTO_KEYSTORE, CONFIG_DIGEST) rather than depending on the
user selecting the implicit dependencies manually?
Sascha
> +
> + backend = &backend_raw->backend;
> backend->save = state_backend_raw_save;
> backend->of_path = xstrdup(of_path);
> backend->path = xstrdup(path);
> @@ -1545,7 +1644,7 @@ int state_backend_raw_file(struct state *state, const char *of_path,
> backend_raw->size_data = sv->start + sv->size;
> backend_raw->offset = offset;
> backend_raw->size = size;
> - backend_raw->size_full = backend_raw->size_data +
> + backend_raw->size_full += backend_raw->size_data +
> sizeof(struct backend_raw_header);
>
> state->backend = backend;
> @@ -1581,6 +1680,8 @@ int state_backend_raw_file(struct state *state, const char *of_path,
> /* ignore return value of load() */
> return 0;
> err:
> + digest_free(backend_raw->backend.digest);
> +
> free(backend_raw);
> return ret;
> }
> --
> 2.6.1
>
>
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>
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