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![Sascha Hauer](/assets/img/avatar_default.png)
HMACs can only be generated on the system the UBIFS image is running on. To support offline signed images we add a PKCS#7 signature to the UBIFS image which can be created by mkfs.ubifs. Both the master node and the superblock need to be authenticated, during normal runtime both are protected with HMACs. For offline signature support however only a single signature is desired. We add a signature covering the superblock node directly behind it. To protect the master node a hash of the master node is added to the superblock which is used when the master node doesn't contain a HMAC. Transition to a read/write filesystem is also supported. During transition first the master node is rewritten with a HMAC (implicitly, it is written anyway as the FS is marked dirty). Afterwards the superblock is rewritten with a HMAC. Once after the image has been mounted read/write it is HMAC only, the signature is no longer required or even present on the filesystem. In an offline signed image the master node is authenticated by the superblock. In a transition to r/w we have to make sure that the master node is rewritten before the superblock node. In this case the master node gets a HMAC and its authenticity no longer depends on the superblock node. There are some cases in which the current code first writes the superblock node though, so with this patch writing of the superblock node is delayed until the master node is written. Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de> Signed-off-by: Richard Weinberger <richard@nod.at>
566 lines
14 KiB
C
566 lines
14 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* This file is part of UBIFS.
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*
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* Copyright (C) 2018 Pengutronix, Sascha Hauer <s.hauer@pengutronix.de>
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*/
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/*
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* This file implements various helper functions for UBIFS authentication support
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*/
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#include <linux/crypto.h>
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#include <linux/verification.h>
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#include <crypto/hash.h>
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#include <crypto/sha.h>
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#include <crypto/algapi.h>
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#include <keys/user-type.h>
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#include <keys/asymmetric-type.h>
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#include "ubifs.h"
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/**
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* ubifs_node_calc_hash - calculate the hash of a UBIFS node
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* @c: UBIFS file-system description object
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* @node: the node to calculate a hash for
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* @hash: the returned hash
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*
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* Returns 0 for success or a negative error code otherwise.
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*/
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int __ubifs_node_calc_hash(const struct ubifs_info *c, const void *node,
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u8 *hash)
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{
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const struct ubifs_ch *ch = node;
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SHASH_DESC_ON_STACK(shash, c->hash_tfm);
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int err;
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shash->tfm = c->hash_tfm;
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err = crypto_shash_digest(shash, node, le32_to_cpu(ch->len), hash);
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if (err < 0)
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return err;
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return 0;
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}
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/**
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* ubifs_hash_calc_hmac - calculate a HMAC from a hash
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* @c: UBIFS file-system description object
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* @hash: the node to calculate a HMAC for
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* @hmac: the returned HMAC
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*
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* Returns 0 for success or a negative error code otherwise.
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*/
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static int ubifs_hash_calc_hmac(const struct ubifs_info *c, const u8 *hash,
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u8 *hmac)
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{
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SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
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int err;
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shash->tfm = c->hmac_tfm;
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err = crypto_shash_digest(shash, hash, c->hash_len, hmac);
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if (err < 0)
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return err;
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return 0;
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}
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/**
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* ubifs_prepare_auth_node - Prepare an authentication node
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* @c: UBIFS file-system description object
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* @node: the node to calculate a hash for
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* @hash: input hash of previous nodes
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*
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* This function prepares an authentication node for writing onto flash.
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* It creates a HMAC from the given input hash and writes it to the node.
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*
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* Returns 0 for success or a negative error code otherwise.
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*/
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int ubifs_prepare_auth_node(struct ubifs_info *c, void *node,
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struct shash_desc *inhash)
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{
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struct ubifs_auth_node *auth = node;
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u8 *hash;
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int err;
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hash = kmalloc(crypto_shash_descsize(c->hash_tfm), GFP_NOFS);
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if (!hash)
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return -ENOMEM;
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{
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SHASH_DESC_ON_STACK(hash_desc, c->hash_tfm);
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hash_desc->tfm = c->hash_tfm;
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ubifs_shash_copy_state(c, inhash, hash_desc);
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err = crypto_shash_final(hash_desc, hash);
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if (err)
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goto out;
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}
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err = ubifs_hash_calc_hmac(c, hash, auth->hmac);
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if (err)
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goto out;
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auth->ch.node_type = UBIFS_AUTH_NODE;
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ubifs_prepare_node(c, auth, ubifs_auth_node_sz(c), 0);
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err = 0;
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out:
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kfree(hash);
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return err;
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}
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static struct shash_desc *ubifs_get_desc(const struct ubifs_info *c,
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struct crypto_shash *tfm)
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{
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struct shash_desc *desc;
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int err;
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if (!ubifs_authenticated(c))
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return NULL;
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desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(tfm), GFP_KERNEL);
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if (!desc)
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return ERR_PTR(-ENOMEM);
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desc->tfm = tfm;
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err = crypto_shash_init(desc);
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if (err) {
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kfree(desc);
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return ERR_PTR(err);
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}
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return desc;
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}
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/**
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* __ubifs_hash_get_desc - get a descriptor suitable for hashing a node
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* @c: UBIFS file-system description object
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*
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* This function returns a descriptor suitable for hashing a node. Free after use
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* with kfree.
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*/
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struct shash_desc *__ubifs_hash_get_desc(const struct ubifs_info *c)
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{
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return ubifs_get_desc(c, c->hash_tfm);
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}
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/**
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* ubifs_bad_hash - Report hash mismatches
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* @c: UBIFS file-system description object
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* @node: the node
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* @hash: the expected hash
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* @lnum: the LEB @node was read from
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* @offs: offset in LEB @node was read from
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*
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* This function reports a hash mismatch when a node has a different hash than
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* expected.
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*/
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void ubifs_bad_hash(const struct ubifs_info *c, const void *node, const u8 *hash,
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int lnum, int offs)
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{
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int len = min(c->hash_len, 20);
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int cropped = len != c->hash_len;
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const char *cont = cropped ? "..." : "";
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u8 calc[UBIFS_HASH_ARR_SZ];
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__ubifs_node_calc_hash(c, node, calc);
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ubifs_err(c, "hash mismatch on node at LEB %d:%d", lnum, offs);
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ubifs_err(c, "hash expected: %*ph%s", len, hash, cont);
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ubifs_err(c, "hash calculated: %*ph%s", len, calc, cont);
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}
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/**
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* __ubifs_node_check_hash - check the hash of a node against given hash
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* @c: UBIFS file-system description object
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* @node: the node
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* @expected: the expected hash
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*
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* This function calculates a hash over a node and compares it to the given hash.
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* Returns 0 if both hashes are equal or authentication is disabled, otherwise a
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* negative error code is returned.
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*/
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int __ubifs_node_check_hash(const struct ubifs_info *c, const void *node,
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const u8 *expected)
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{
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u8 calc[UBIFS_HASH_ARR_SZ];
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int err;
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err = __ubifs_node_calc_hash(c, node, calc);
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if (err)
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return err;
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if (ubifs_check_hash(c, expected, calc))
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return -EPERM;
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return 0;
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}
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/**
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* ubifs_sb_verify_signature - verify the signature of a superblock
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* @c: UBIFS file-system description object
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* @sup: The superblock node
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*
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* To support offline signed images the superblock can be signed with a
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* PKCS#7 signature. The signature is placed directly behind the superblock
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* node in an ubifs_sig_node.
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*
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* Returns 0 when the signature can be successfully verified or a negative
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* error code if not.
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*/
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int ubifs_sb_verify_signature(struct ubifs_info *c,
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const struct ubifs_sb_node *sup)
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{
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int err;
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struct ubifs_scan_leb *sleb;
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struct ubifs_scan_node *snod;
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const struct ubifs_sig_node *signode;
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sleb = ubifs_scan(c, UBIFS_SB_LNUM, UBIFS_SB_NODE_SZ, c->sbuf, 0);
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if (IS_ERR(sleb)) {
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err = PTR_ERR(sleb);
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return err;
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}
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if (sleb->nodes_cnt == 0) {
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ubifs_err(c, "Unable to find signature node");
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err = -EINVAL;
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goto out_destroy;
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}
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snod = list_first_entry(&sleb->nodes, struct ubifs_scan_node, list);
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if (snod->type != UBIFS_SIG_NODE) {
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ubifs_err(c, "Signature node is of wrong type");
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err = -EINVAL;
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goto out_destroy;
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}
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signode = snod->node;
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if (le32_to_cpu(signode->len) > snod->len + sizeof(struct ubifs_sig_node)) {
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ubifs_err(c, "invalid signature len %d", le32_to_cpu(signode->len));
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err = -EINVAL;
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goto out_destroy;
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}
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if (le32_to_cpu(signode->type) != UBIFS_SIGNATURE_TYPE_PKCS7) {
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ubifs_err(c, "Signature type %d is not supported\n",
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le32_to_cpu(signode->type));
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err = -EINVAL;
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goto out_destroy;
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}
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err = verify_pkcs7_signature(sup, sizeof(struct ubifs_sb_node),
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signode->sig, le32_to_cpu(signode->len),
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NULL, VERIFYING_UNSPECIFIED_SIGNATURE,
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NULL, NULL);
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if (err)
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ubifs_err(c, "Failed to verify signature");
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else
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ubifs_msg(c, "Successfully verified super block signature");
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out_destroy:
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ubifs_scan_destroy(sleb);
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return err;
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}
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/**
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* ubifs_init_authentication - initialize UBIFS authentication support
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* @c: UBIFS file-system description object
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*
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* This function returns 0 for success or a negative error code otherwise.
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*/
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int ubifs_init_authentication(struct ubifs_info *c)
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{
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struct key *keyring_key;
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const struct user_key_payload *ukp;
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int err;
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char hmac_name[CRYPTO_MAX_ALG_NAME];
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if (!c->auth_hash_name) {
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ubifs_err(c, "authentication hash name needed with authentication");
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return -EINVAL;
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}
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c->auth_hash_algo = match_string(hash_algo_name, HASH_ALGO__LAST,
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c->auth_hash_name);
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if ((int)c->auth_hash_algo < 0) {
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ubifs_err(c, "Unknown hash algo %s specified",
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c->auth_hash_name);
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return -EINVAL;
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}
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snprintf(hmac_name, CRYPTO_MAX_ALG_NAME, "hmac(%s)",
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c->auth_hash_name);
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keyring_key = request_key(&key_type_logon, c->auth_key_name, NULL);
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if (IS_ERR(keyring_key)) {
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ubifs_err(c, "Failed to request key: %ld",
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PTR_ERR(keyring_key));
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return PTR_ERR(keyring_key);
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}
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down_read(&keyring_key->sem);
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if (keyring_key->type != &key_type_logon) {
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ubifs_err(c, "key type must be logon");
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err = -ENOKEY;
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goto out;
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}
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ukp = user_key_payload_locked(keyring_key);
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if (!ukp) {
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/* key was revoked before we acquired its semaphore */
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err = -EKEYREVOKED;
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goto out;
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}
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c->hash_tfm = crypto_alloc_shash(c->auth_hash_name, 0, 0);
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if (IS_ERR(c->hash_tfm)) {
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err = PTR_ERR(c->hash_tfm);
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ubifs_err(c, "Can not allocate %s: %d",
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c->auth_hash_name, err);
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goto out;
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}
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c->hash_len = crypto_shash_digestsize(c->hash_tfm);
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if (c->hash_len > UBIFS_HASH_ARR_SZ) {
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ubifs_err(c, "hash %s is bigger than maximum allowed hash size (%d > %d)",
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c->auth_hash_name, c->hash_len, UBIFS_HASH_ARR_SZ);
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err = -EINVAL;
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goto out_free_hash;
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}
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c->hmac_tfm = crypto_alloc_shash(hmac_name, 0, 0);
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if (IS_ERR(c->hmac_tfm)) {
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err = PTR_ERR(c->hmac_tfm);
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ubifs_err(c, "Can not allocate %s: %d", hmac_name, err);
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goto out_free_hash;
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}
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c->hmac_desc_len = crypto_shash_digestsize(c->hmac_tfm);
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if (c->hmac_desc_len > UBIFS_HMAC_ARR_SZ) {
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ubifs_err(c, "hmac %s is bigger than maximum allowed hmac size (%d > %d)",
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hmac_name, c->hmac_desc_len, UBIFS_HMAC_ARR_SZ);
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err = -EINVAL;
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goto out_free_hash;
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}
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err = crypto_shash_setkey(c->hmac_tfm, ukp->data, ukp->datalen);
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if (err)
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goto out_free_hmac;
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c->authenticated = true;
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c->log_hash = ubifs_hash_get_desc(c);
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if (IS_ERR(c->log_hash))
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goto out_free_hmac;
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err = 0;
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out_free_hmac:
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if (err)
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crypto_free_shash(c->hmac_tfm);
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out_free_hash:
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if (err)
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crypto_free_shash(c->hash_tfm);
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out:
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up_read(&keyring_key->sem);
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key_put(keyring_key);
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return err;
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}
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/**
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* __ubifs_exit_authentication - release resource
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* @c: UBIFS file-system description object
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*
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* This function releases the authentication related resources.
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*/
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void __ubifs_exit_authentication(struct ubifs_info *c)
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{
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if (!ubifs_authenticated(c))
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return;
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crypto_free_shash(c->hmac_tfm);
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crypto_free_shash(c->hash_tfm);
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kfree(c->log_hash);
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}
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/**
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* ubifs_node_calc_hmac - calculate the HMAC of a UBIFS node
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* @c: UBIFS file-system description object
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* @node: the node to insert a HMAC into.
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* @len: the length of the node
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* @ofs_hmac: the offset in the node where the HMAC is inserted
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* @hmac: returned HMAC
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*
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* This function calculates a HMAC of a UBIFS node. The HMAC is expected to be
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* embedded into the node, so this area is not covered by the HMAC. Also not
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* covered is the UBIFS_NODE_MAGIC and the CRC of the node.
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*/
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static int ubifs_node_calc_hmac(const struct ubifs_info *c, const void *node,
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int len, int ofs_hmac, void *hmac)
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{
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SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
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int hmac_len = c->hmac_desc_len;
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int err;
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ubifs_assert(c, ofs_hmac > 8);
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ubifs_assert(c, ofs_hmac + hmac_len < len);
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shash->tfm = c->hmac_tfm;
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err = crypto_shash_init(shash);
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if (err)
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return err;
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|
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/* behind common node header CRC up to HMAC begin */
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err = crypto_shash_update(shash, node + 8, ofs_hmac - 8);
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if (err < 0)
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return err;
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|
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/* behind HMAC, if any */
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if (len - ofs_hmac - hmac_len > 0) {
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err = crypto_shash_update(shash, node + ofs_hmac + hmac_len,
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len - ofs_hmac - hmac_len);
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if (err < 0)
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return err;
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}
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|
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return crypto_shash_final(shash, hmac);
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}
|
|
|
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/**
|
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* __ubifs_node_insert_hmac - insert a HMAC into a UBIFS node
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* @c: UBIFS file-system description object
|
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* @node: the node to insert a HMAC into.
|
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* @len: the length of the node
|
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* @ofs_hmac: the offset in the node where the HMAC is inserted
|
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*
|
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* This function inserts a HMAC at offset @ofs_hmac into the node given in
|
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* @node.
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*
|
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* This function returns 0 for success or a negative error code otherwise.
|
|
*/
|
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int __ubifs_node_insert_hmac(const struct ubifs_info *c, void *node, int len,
|
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int ofs_hmac)
|
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{
|
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return ubifs_node_calc_hmac(c, node, len, ofs_hmac, node + ofs_hmac);
|
|
}
|
|
|
|
/**
|
|
* __ubifs_node_verify_hmac - verify the HMAC of UBIFS node
|
|
* @c: UBIFS file-system description object
|
|
* @node: the node to insert a HMAC into.
|
|
* @len: the length of the node
|
|
* @ofs_hmac: the offset in the node where the HMAC is inserted
|
|
*
|
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* This function verifies the HMAC at offset @ofs_hmac of the node given in
|
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* @node. Returns 0 if successful or a negative error code otherwise.
|
|
*/
|
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int __ubifs_node_verify_hmac(const struct ubifs_info *c, const void *node,
|
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int len, int ofs_hmac)
|
|
{
|
|
int hmac_len = c->hmac_desc_len;
|
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u8 *hmac;
|
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int err;
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|
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hmac = kmalloc(hmac_len, GFP_NOFS);
|
|
if (!hmac)
|
|
return -ENOMEM;
|
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|
|
err = ubifs_node_calc_hmac(c, node, len, ofs_hmac, hmac);
|
|
if (err)
|
|
return err;
|
|
|
|
err = crypto_memneq(hmac, node + ofs_hmac, hmac_len);
|
|
|
|
kfree(hmac);
|
|
|
|
if (!err)
|
|
return 0;
|
|
|
|
return -EPERM;
|
|
}
|
|
|
|
int __ubifs_shash_copy_state(const struct ubifs_info *c, struct shash_desc *src,
|
|
struct shash_desc *target)
|
|
{
|
|
u8 *state;
|
|
int err;
|
|
|
|
state = kmalloc(crypto_shash_descsize(src->tfm), GFP_NOFS);
|
|
if (!state)
|
|
return -ENOMEM;
|
|
|
|
err = crypto_shash_export(src, state);
|
|
if (err)
|
|
goto out;
|
|
|
|
err = crypto_shash_import(target, state);
|
|
|
|
out:
|
|
kfree(state);
|
|
|
|
return err;
|
|
}
|
|
|
|
/**
|
|
* ubifs_hmac_wkm - Create a HMAC of the well known message
|
|
* @c: UBIFS file-system description object
|
|
* @hmac: The HMAC of the well known message
|
|
*
|
|
* This function creates a HMAC of a well known message. This is used
|
|
* to check if the provided key is suitable to authenticate a UBIFS
|
|
* image. This is only a convenience to the user to provide a better
|
|
* error message when the wrong key is provided.
|
|
*
|
|
* This function returns 0 for success or a negative error code otherwise.
|
|
*/
|
|
int ubifs_hmac_wkm(struct ubifs_info *c, u8 *hmac)
|
|
{
|
|
SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
|
|
int err;
|
|
const char well_known_message[] = "UBIFS";
|
|
|
|
if (!ubifs_authenticated(c))
|
|
return 0;
|
|
|
|
shash->tfm = c->hmac_tfm;
|
|
|
|
err = crypto_shash_init(shash);
|
|
if (err)
|
|
return err;
|
|
|
|
err = crypto_shash_update(shash, well_known_message,
|
|
sizeof(well_known_message) - 1);
|
|
if (err < 0)
|
|
return err;
|
|
|
|
err = crypto_shash_final(shash, hmac);
|
|
if (err)
|
|
return err;
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* ubifs_hmac_zero - test if a HMAC is zero
|
|
* @c: UBIFS file-system description object
|
|
* @hmac: the HMAC to test
|
|
*
|
|
* This function tests if a HMAC is zero and returns true if it is
|
|
* and false otherwise.
|
|
*/
|
|
bool ubifs_hmac_zero(struct ubifs_info *c, const u8 *hmac)
|
|
{
|
|
return !memchr_inv(hmac, 0, c->hmac_desc_len);
|
|
}
|