Re: [RFC v2.0 3/3] evm: digital signature support

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Please ignore this patch. It was sent by mistake...
Check:
evm: digital signature verification support

- Dmitry

On Tue, Sep 6, 2011 at 4:11 PM, Dmitry Kasatkin
<dmitry.kasatkin@xxxxxxxxx> wrote:
> When building an image, which has to be flashed to different devices,
> an HMAC cannot be used to sign file metadata, as the HMAC key is different
> on every device. File metadata can be protected using digital signature.
> This patch enables RSA signature based integrity verification.
>
> Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxx>
> Acked-by: Mimi Zohar <zohar@xxxxxxxxxx>
> ---
>  security/integrity/evm/Kconfig      |   14 ++++
>  security/integrity/evm/evm.h        |   12 ++++
>  security/integrity/evm/evm_crypto.c |   66 ++++++++++++++-----
>  security/integrity/evm/evm_main.c   |  125 +++++++++++++++++++++++++++++++----
>  4 files changed, 187 insertions(+), 30 deletions(-)
>
> diff --git a/security/integrity/evm/Kconfig b/security/integrity/evm/Kconfig
> index 884617d..84eea75 100644
> --- a/security/integrity/evm/Kconfig
> +++ b/security/integrity/evm/Kconfig
> @@ -12,3 +12,17 @@ config EVM
>          integrity attacks.
>
>          If you are unsure how to answer this question, answer N.
> +
> +config EVM_DIGSIG
> +       boolean "EVM Digital Signature support"
> +       depends on EVM
> +       default n
> +       select CRYPTO_KSIGN_RSA
> +       help
> +         When building an image, which has to be flashed to different
> +         devices, an HMAC cannot be used to sign file metadata, as
> +         the HMAC key is different on every device.
> +         File metadata can be protected using digital signature.
> +         This option enables RSA signature based integrity verification.
> +
> +         If unsure, say N.
> diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
> index d320f51..c885247 100644
> --- a/security/integrity/evm/evm.h
> +++ b/security/integrity/evm/evm.h
> @@ -12,14 +12,21 @@
>  * File: evm.h
>  *
>  */
> +
> +#ifndef __INTEGRITY_EVM_H
> +#define __INTEGRITY_EVM_H
> +
>  #include <linux/xattr.h>
>  #include <linux/security.h>
> +
>  #include "../integrity.h"
>
>  extern int evm_initialized;
>  extern char *evm_hmac;
> +extern char *evm_hash;
>
>  extern struct crypto_shash *hmac_tfm;
> +extern struct crypto_shash *hash_tfm;
>
>  /* List of EVM protected security xattrs */
>  extern char *evm_config_xattrnames[];
> @@ -32,7 +39,12 @@ extern int evm_update_evmxattr(struct dentry *dentry,
>  extern int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
>                         const char *req_xattr_value,
>                         size_t req_xattr_value_len, char *digest);
> +extern int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
> +                        const char *req_xattr_value,
> +                        size_t req_xattr_value_len, char *digest);
>  extern int evm_init_hmac(struct inode *inode, const struct xattr *xattr,
>                         char *hmac_val);
>  extern int evm_init_secfs(void);
>  extern void evm_cleanup_secfs(void);
> +
> +#endif
> diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
> index 5dd5b140..847a2d7 100644
> --- a/security/integrity/evm/evm_crypto.c
> +++ b/security/integrity/evm/evm_crypto.c
> @@ -26,34 +26,48 @@ static unsigned char evmkey[MAX_KEY_SIZE];
>  static int evmkey_len = MAX_KEY_SIZE;
>
>  struct crypto_shash *hmac_tfm;
> +struct crypto_shash *hash_tfm;
>
> -static struct shash_desc *init_desc(void)
> +static struct shash_desc *init_desc(const char type)
>  {
>        int rc;
> +       char *algo;
> +       struct crypto_shash **tfm;
>        struct shash_desc *desc;
>
> -       if (hmac_tfm == NULL) {
> -               hmac_tfm = crypto_alloc_shash(evm_hmac, 0, CRYPTO_ALG_ASYNC);
> -               if (IS_ERR(hmac_tfm)) {
> +       if (type == EVM_XATTR_HMAC) {
> +               tfm = &hmac_tfm;
> +               algo = evm_hmac;
> +       } else {
> +               tfm = &hash_tfm;
> +               algo = evm_hash;
> +       }
> +
> +       if (*tfm == NULL) {
> +               *tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC);
> +               if (IS_ERR(*tfm)) {
>                        pr_err("Can not allocate %s (reason: %ld)\n",
> -                              evm_hmac, PTR_ERR(hmac_tfm));
> -                       rc = PTR_ERR(hmac_tfm);
> -                       hmac_tfm = NULL;
> +                              algo, PTR_ERR(*tfm));
> +                       rc = PTR_ERR(*tfm);
> +                       *tfm = NULL;
>                        return ERR_PTR(rc);
>                }
>        }
>
> -       desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(hmac_tfm),
> +       desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
>                        GFP_KERNEL);
>        if (!desc)
>                return ERR_PTR(-ENOMEM);
>
> -       desc->tfm = hmac_tfm;
> +       desc->tfm = *tfm;
>        desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
>
> -       rc = crypto_shash_setkey(hmac_tfm, evmkey, evmkey_len);
> -       if (rc)
> -               goto out;
> +       if (type == EVM_XATTR_HMAC) {
> +               rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
> +               if (rc)
> +                       goto out;
> +       }
> +
>        rc = crypto_shash_init(desc);
>  out:
>        if (rc) {
> @@ -97,9 +111,11 @@ static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
>  * the hmac using the requested xattr value. Don't alloc/free memory for
>  * each xattr, but attempt to re-use the previously allocated memory.
>  */
> -int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
> -                 const char *req_xattr_value, size_t req_xattr_value_len,
> -                 char *digest)
> +static int evm_calc_hmac_or_hash(struct dentry *dentry,
> +                               const char *req_xattr_name,
> +                               const char *req_xattr_value,
> +                               size_t req_xattr_value_len,
> +                               char type, char *digest)
>  {
>        struct inode *inode = dentry->d_inode;
>        struct shash_desc *desc;
> @@ -111,7 +127,7 @@ int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
>
>        if (!inode->i_op || !inode->i_op->getxattr)
>                return -EOPNOTSUPP;
> -       desc = init_desc();
> +       desc = init_desc(type);
>        if (IS_ERR(desc))
>                return PTR_ERR(desc);
>
> @@ -145,6 +161,22 @@ out:
>        return error;
>  }
>
> +int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
> +                 const char *req_xattr_value, size_t req_xattr_value_len,
> +                 char *digest)
> +{
> +       return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
> +                               req_xattr_value_len, EVM_XATTR_HMAC, digest);
> +}
> +
> +int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
> +                 const char *req_xattr_value, size_t req_xattr_value_len,
> +                 char *digest)
> +{
> +       return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
> +                               req_xattr_value_len, IMA_XATTR_DIGEST, digest);
> +}
> +
>  /*
>  * Calculate the hmac and update security.evm xattr
>  *
> @@ -175,7 +207,7 @@ int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
>  {
>        struct shash_desc *desc;
>
> -       desc = init_desc();
> +       desc = init_desc(EVM_XATTR_HMAC);
>        if (IS_ERR(desc)) {
>                printk(KERN_INFO "init_desc failed\n");
>                return PTR_ERR(desc);
> diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
> index 8b2eff9..d8ac109 100644
> --- a/security/integrity/evm/evm_main.c
> +++ b/security/integrity/evm/evm_main.c
> @@ -18,6 +18,8 @@
>  #include <linux/crypto.h>
>  #include <linux/xattr.h>
>  #include <linux/integrity.h>
> +#include <linux/key-type.h>
> +#include <linux/crypto/ksign.h>
>  #include <linux/evm.h>
>  #include <crypto/hash.h>
>  #include "evm.h"
> @@ -25,6 +27,7 @@
>  int evm_initialized;
>
>  char *evm_hmac = "hmac(sha1)";
> +char *evm_hash = "sha1";
>
>  char *evm_config_xattrnames[] = {
>  #ifdef CONFIG_SECURITY_SELINUX
> @@ -40,6 +43,8 @@ char *evm_config_xattrnames[] = {
>        NULL
>  };
>
> +static struct key *evm_keyring;
> +
>  static int evm_fixmode;
>  static int __init evm_set_fixmode(char *str)
>  {
> @@ -49,6 +54,56 @@ static int __init evm_set_fixmode(char *str)
>  }
>  __setup("evm=", evm_set_fixmode);
>
> +static int evm_find_protected_xattrs(struct dentry *dentry)
> +{
> +       struct inode *inode = dentry->d_inode;
> +       char **xattr;
> +       int error;
> +       int count = 0;
> +
> +       if (!inode->i_op || !inode->i_op->getxattr)
> +               return -EOPNOTSUPP;
> +
> +       for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
> +               error = inode->i_op->getxattr(dentry, *xattr, NULL, 0);
> +               if (error < 0) {
> +                       if (error == -ENODATA)
> +                               continue;
> +                       return error;
> +               }
> +               count++;
> +       }
> +
> +       return count;
> +}
> +
> +#ifdef CONFIG_EVM_DIGSIG
> +
> +int evm_sign_verify(const char *sig, int siglen,
> +                      const char *digest, int digestlen)
> +{
> +       if (!evm_keyring) {
> +               evm_keyring = request_key(&key_type_keyring, "_evm", NULL);
> +               if (IS_ERR(evm_keyring)) {
> +                       pr_err("no evm keyring: %ld\n", PTR_ERR(evm_keyring));
> +                       evm_keyring = NULL;
> +                       return PTR_ERR(evm_keyring);
> +               }
> +       }
> +
> +       return ksign_verify(evm_keyring, sig, siglen, digest, digestlen);
> +}
> +
> +#else
> +
> +static inline int evm_sign_verify(const char *sig, int siglen,
> +                      const char *digest, int digestlen)
> +{
> +       return -EOPNOTSUPP;
> +}
> +
> +#endif /* CONFIG_EVM_DIGSIG */
> +
>  /*
>  * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
>  *
> @@ -68,32 +123,71 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
>                                             size_t xattr_value_len,
>                                             struct integrity_iint_cache *iint)
>  {
> -       struct evm_ima_xattr_data xattr_data;
> +       struct evm_ima_xattr_data *xattr_data = NULL;
> +       struct evm_ima_xattr_data calc;
>        enum integrity_status evm_status = INTEGRITY_PASS;
> -       int rc;
> +       int rc, xattr_len;
>
>        if (iint && iint->evm_status == INTEGRITY_PASS)
>                return iint->evm_status;
>
>        /* if status is not PASS, try to check again - against -ENOMEM */
>
> -       rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
> -                          xattr_value_len, xattr_data.digest);
> -       if (rc < 0) {
> -               evm_status = (rc == -ENODATA)
> -                   ? INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
> +       /* first need to know the sig type */
> +       rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
> +                               GFP_NOFS);
> +       if (rc <= 0) {
> +               if (rc == 0)
> +                       evm_status = INTEGRITY_FAIL; /* empty */
> +               else if (rc == -ENODATA) {
> +                       rc = evm_find_protected_xattrs(dentry);
> +                       if (rc > 0)
> +                               evm_status = INTEGRITY_NOLABEL;
> +                       else if (rc == 0)
> +                               evm_status = INTEGRITY_NOXATTRS; /* new file */
> +               }
>                goto out;
>        }
>
> -       xattr_data.type = EVM_XATTR_HMAC;
> -       rc = vfs_xattr_cmp(dentry, XATTR_NAME_EVM, (u8 *)&xattr_data,
> -                          sizeof xattr_data, GFP_NOFS);
> -       if (rc < 0)
> -               evm_status = (rc == -ENODATA)
> -                   ? INTEGRITY_NOLABEL : INTEGRITY_FAIL;
> +       xattr_len = rc - 1;
> +
> +       /* check value type */
> +       switch (xattr_data->type) {
> +       case EVM_XATTR_HMAC:
> +               rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
> +                                  xattr_value_len, calc.digest);
> +               if (rc)
> +                       break;
> +               rc = memcmp(xattr_data->digest, calc.digest,
> +                           sizeof(calc.digest));
> +               if (rc)
> +                       rc = -EINVAL;
> +               break;
> +       case EVM_IMA_XATTR_DIGSIG:
> +               rc = evm_calc_hash(dentry, xattr_name, xattr_value,
> +                               xattr_value_len, calc.digest);
> +               if (rc)
> +                       break;
> +               rc = evm_sign_verify(xattr_data->digest, xattr_len,
> +                                    calc.digest, sizeof(calc.digest));
> +               if (!rc) {
> +                       /* we probably want to replace rsa with hmac here */
> +                       evm_update_evmxattr(dentry, xattr_name, xattr_value,
> +                                  xattr_value_len);
> +               }
> +               break;
> +       default:
> +               rc = -EINVAL;
> +               break;
> +       }
> +
> +       if (rc)
> +               evm_status = (rc == -ENODATA) ?
> +                               INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
>  out:
>        if (iint)
>                iint->evm_status = evm_status;
> +       kfree(xattr_data);
>        return evm_status;
>  }
>
> @@ -357,6 +451,8 @@ static int __init init_evm(void)
>                printk(KERN_INFO "EVM: Error registering secfs\n");
>                goto err;
>        }
> +
> +       return 0;
>  err:
>        return error;
>  }
> @@ -364,8 +460,11 @@ err:
>  static void __exit cleanup_evm(void)
>  {
>        evm_cleanup_secfs();
> +       key_put(evm_keyring);
>        if (hmac_tfm)
>                crypto_free_shash(hmac_tfm);
> +       if (hash_tfm)
> +               crypto_free_shash(hash_tfm);
>  }
>
>  /*
> --
> 1.7.4.1
>
>
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