// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2005-2010 IBM Corporation
 *
 * Author:
 * Mimi Zohar <zohar@us.ibm.com>
 * Kylene Hall <kjhall@us.ibm.com>
 *
 * File: evm_main.c
 *      implements evm_inode_setxattr, evm_inode_post_setxattr,
 *      evm_inode_removexattr, and evm_verifyxattr
 */

#include <linux/init.h>
#include <linux/crypto.h>
#include <linux/audit.h>
#include <linux/xattr.h>
#include <linux/integrity.h>
#include <linux/evm.h>
#include <linux/magic.h>

#include <crypto/hash.h>
#include <crypto/hash_info.h>
#include <crypto/algapi.h>
#include "evm.h"

int evm_initialized;

static const char * const integrity_status_msg[] = {
        "pass", "pass_immutable", "fail", "no_label", "no_xattrs", "unknown"
};
int evm_hmac_attrs;

static struct xattr_list evm_config_default_xattrnames[] = {
#ifdef CONFIG_SECURITY_SELINUX
        {.name = XATTR_NAME_SELINUX},
#endif
#ifdef CONFIG_SECURITY_SMACK
        {.name = XATTR_NAME_SMACK},
#ifdef CONFIG_EVM_EXTRA_SMACK_XATTRS
        {.name = XATTR_NAME_SMACKEXEC},
        {.name = XATTR_NAME_SMACKTRANSMUTE},
        {.name = XATTR_NAME_SMACKMMAP},
#endif
#endif
#ifdef CONFIG_SECURITY_APPARMOR
        {.name = XATTR_NAME_APPARMOR},
#endif
#ifdef CONFIG_IMA_APPRAISE
        {.name = XATTR_NAME_IMA},
#endif
        {.name = XATTR_NAME_CAPS},
};

LIST_HEAD(evm_config_xattrnames);

static int evm_fixmode;
static int __init evm_set_fixmode(char *str)
{
        if (strncmp(str, "fix", 3) == 0)
                evm_fixmode = 1;
        else
                pr_err("invalid \"%s\" mode", str);

        return 0;
}
__setup("evm=", evm_set_fixmode);

static void __init evm_init_config(void)
{
        int i, xattrs;

        xattrs = ARRAY_SIZE(evm_config_default_xattrnames);

        pr_info("Initialising EVM extended attributes:\n");
        for (i = 0; i < xattrs; i++) {
                pr_info("%s\n", evm_config_default_xattrnames[i].name);
                list_add_tail(&evm_config_default_xattrnames[i].list,
                              &evm_config_xattrnames);
        }

#ifdef CONFIG_EVM_ATTR_FSUUID
        evm_hmac_attrs |= EVM_ATTR_FSUUID;
#endif
        pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
}

static bool evm_key_loaded(void)
{
        return (bool)(evm_initialized & EVM_KEY_MASK);
}

static int evm_find_protected_xattrs(struct dentry *dentry)
{
        struct inode *inode = d_backing_inode(dentry);
        struct xattr_list *xattr;
        int error;
        int count = 0;

        if (!(inode->i_opflags & IOP_XATTR))
                return -EOPNOTSUPP;

        list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
                error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
                if (error < 0) {
                        if (error == -ENODATA)
                                continue;
                        return error;
                }
                count++;
        }

        return count;
}

/*
 * evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
 *
 * Compute the HMAC on the dentry's protected set of extended attributes
 * and compare it against the stored security.evm xattr.
 *
 * For performance:
 * - use the previoulsy retrieved xattr value and length to calculate the
 *   HMAC.)
 * - cache the verification result in the iint, when available.
 *
 * Returns integrity status
 */
static enum integrity_status evm_verify_hmac(struct dentry *dentry,
                                             const char *xattr_name,
                                             char *xattr_value,
                                             size_t xattr_value_len,
                                             struct integrity_iint_cache *iint)
{
        struct evm_ima_xattr_data *xattr_data = NULL;
        struct signature_v2_hdr *hdr;
        enum integrity_status evm_status = INTEGRITY_PASS;
        struct evm_digest digest;
        struct inode *inode;
        int rc, xattr_len;

        if (iint && (iint->evm_status == INTEGRITY_PASS ||
                     iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
                return iint->evm_status;

        /* if status is not PASS, try to check again - against -ENOMEM */

        /* first need to know the sig type */
        rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
                                GFP_NOFS);
        if (rc <= 0) {
                evm_status = INTEGRITY_FAIL;
                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 */
                } else if (rc == -EOPNOTSUPP) {
                        evm_status = INTEGRITY_UNKNOWN;
                }
                goto out;
        }

        xattr_len = rc;

        /* check value type */
        switch (xattr_data->type) {
        case EVM_XATTR_HMAC:
                if (xattr_len != sizeof(struct evm_xattr)) {
                        evm_status = INTEGRITY_FAIL;
                        goto out;
                }

                digest.hdr.algo = HASH_ALGO_SHA1;
                rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
                                   xattr_value_len, &digest);
                if (rc)
                        break;
                rc = crypto_memneq(xattr_data->data, digest.digest,
                                   SHA1_DIGEST_SIZE);
                if (rc)
                        rc = -EINVAL;
                break;
        case EVM_IMA_XATTR_DIGSIG:
        case EVM_XATTR_PORTABLE_DIGSIG:
                /* accept xattr with non-empty signature field */
                if (xattr_len <= sizeof(struct signature_v2_hdr)) {
                        evm_status = INTEGRITY_FAIL;
                        goto out;
                }

                hdr = (struct signature_v2_hdr *)xattr_data;
                digest.hdr.algo = hdr->hash_algo;
                rc = evm_calc_hash(dentry, xattr_name, xattr_value,
                                   xattr_value_len, xattr_data->type, &digest);
                if (rc)
                        break;
                rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
                                        (const char *)xattr_data, xattr_len,
                                        digest.digest, digest.hdr.length);
                if (!rc) {
                        inode = d_backing_inode(dentry);

                        if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) {
                                if (iint)
                                        iint->flags |= EVM_IMMUTABLE_DIGSIG;
                                evm_status = INTEGRITY_PASS_IMMUTABLE;
                        } else if (!IS_RDONLY(inode) &&
                                   !(inode->i_sb->s_readonly_remount) &&
                                   !IS_IMMUTABLE(inode)) {
                                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;
}

static int evm_protected_xattr(const char *req_xattr_name)
{
        int namelen;
        int found = 0;
        struct xattr_list *xattr;

        namelen = strlen(req_xattr_name);
        list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
                if ((strlen(xattr->name) == namelen)
                    && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
                        found = 1;
                        break;
                }
                if (strncmp(req_xattr_name,
                            xattr->name + XATTR_SECURITY_PREFIX_LEN,
                            strlen(req_xattr_name)) == 0) {
                        found = 1;
                        break;
                }
        }

        return found;
}

/**
 * evm_verifyxattr - verify the integrity of the requested xattr
 * @dentry: object of the verify xattr
 * @xattr_name: requested xattr
 * @xattr_value: requested xattr value
 * @xattr_value_len: requested xattr value length
 *
 * Calculate the HMAC for the given dentry and verify it against the stored
 * security.evm xattr. For performance, use the xattr value and length
 * previously retrieved to calculate the HMAC.
 *
 * Returns the xattr integrity status.
 *
 * This function requires the caller to lock the inode's i_mutex before it
 * is executed.
 */
enum integrity_status evm_verifyxattr(struct dentry *dentry,
                                      const char *xattr_name,
                                      void *xattr_value, size_t xattr_value_len,
                                      struct integrity_iint_cache *iint)
{
        if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
                return INTEGRITY_UNKNOWN;

        if (!iint) {
                iint = integrity_iint_find(d_backing_inode(dentry));
                if (!iint)
                        return INTEGRITY_UNKNOWN;
        }
        return evm_verify_hmac(dentry, xattr_name, xattr_value,
                                 xattr_value_len, iint);
}
EXPORT_SYMBOL_GPL(evm_verifyxattr);

/*
 * evm_verify_current_integrity - verify the dentry's metadata integrity
 * @dentry: pointer to the affected dentry
 *
 * Verify and return the dentry's metadata integrity. The exceptions are
 * before EVM is initialized or in 'fix' mode.
 */
static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
{
        struct inode *inode = d_backing_inode(dentry);

        if (!evm_key_loaded() || !S_ISREG(inode->i_mode) || evm_fixmode)
                return 0;
        return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
}

/*
 * evm_protect_xattr - protect the EVM extended attribute
 *
 * Prevent security.evm from being modified or removed without the
 * necessary permissions or when the existing value is invalid.
 *
 * The posix xattr acls are 'system' prefixed, which normally would not
 * affect security.evm.  An interesting side affect of writing posix xattr
 * acls is their modifying of the i_mode, which is included in security.evm.
 * For posix xattr acls only, permit security.evm, even if it currently
 * doesn't exist, to be updated unless the EVM signature is immutable.
 */
static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
                             const void *xattr_value, size_t xattr_value_len)
{
        enum integrity_status evm_status;

        if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
                if (!capable(CAP_SYS_ADMIN))
                        return -EPERM;
        } else if (!evm_protected_xattr(xattr_name)) {
                if (!posix_xattr_acl(xattr_name))
                        return 0;
                evm_status = evm_verify_current_integrity(dentry);
                if ((evm_status == INTEGRITY_PASS) ||
                    (evm_status == INTEGRITY_NOXATTRS))
                        return 0;
                goto out;
        }

        evm_status = evm_verify_current_integrity(dentry);
        if (evm_status == INTEGRITY_NOXATTRS) {
                struct integrity_iint_cache *iint;

                iint = integrity_iint_find(d_backing_inode(dentry));
                if (iint && (iint->flags & IMA_NEW_FILE))
                        return 0;

                /* exception for pseudo filesystems */
                if (dentry->d_sb->s_magic == TMPFS_MAGIC
                    || dentry->d_sb->s_magic == SYSFS_MAGIC)
                        return 0;

                integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
                                    dentry->d_inode, dentry->d_name.name,
                                    "update_metadata",
                                    integrity_status_msg[evm_status],
                                    -EPERM, 0);
        }
out:
        if (evm_status != INTEGRITY_PASS)
                integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
                                    dentry->d_name.name, "appraise_metadata",
                                    integrity_status_msg[evm_status],
                                    -EPERM, 0);
        return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
}

/**
 * evm_inode_setxattr - protect the EVM extended attribute
 * @dentry: pointer to the affected dentry
 * @xattr_name: pointer to the affected extended attribute name
 * @xattr_value: pointer to the new extended attribute value
 * @xattr_value_len: pointer to the new extended attribute value length
 *
 * Before allowing the 'security.evm' protected xattr to be updated,
 * verify the existing value is valid.  As only the kernel should have
 * access to the EVM encrypted key needed to calculate the HMAC, prevent
 * userspace from writing HMAC value.  Writing 'security.evm' requires
 * requires CAP_SYS_ADMIN privileges.
 */
int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
                       const void *xattr_value, size_t xattr_value_len)
{
        const struct evm_ima_xattr_data *xattr_data = xattr_value;

        /* Policy permits modification of the protected xattrs even though
         * there's no HMAC key loaded
         */
        if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
                return 0;

        if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
                if (!xattr_value_len)
                        return -EINVAL;
                if (xattr_data->type != EVM_IMA_XATTR_DIGSIG &&
                    xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG)
                        return -EPERM;
        }
        return evm_protect_xattr(dentry, xattr_name, xattr_value,
                                 xattr_value_len);
}

/**
 * evm_inode_removexattr - protect the EVM extended attribute
 * @dentry: pointer to the affected dentry
 * @xattr_name: pointer to the affected extended attribute name
 *
 * Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
 * the current value is valid.
 */
int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
{
        /* Policy permits modification of the protected xattrs even though
         * there's no HMAC key loaded
         */
        if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
                return 0;

        return evm_protect_xattr(dentry, xattr_name, NULL, 0);
}

static void evm_reset_status(struct inode *inode)
{
        struct integrity_iint_cache *iint;

        iint = integrity_iint_find(inode);
        if (iint)
                iint->evm_status = INTEGRITY_UNKNOWN;
}

/**
 * evm_inode_post_setxattr - update 'security.evm' to reflect the changes
 * @dentry: pointer to the affected dentry
 * @xattr_name: pointer to the affected extended attribute name
 * @xattr_value: pointer to the new extended attribute value
 * @xattr_value_len: pointer to the new extended attribute value length
 *
 * Update the HMAC stored in 'security.evm' to reflect the change.
 *
 * No need to take the i_mutex lock here, as this function is called from
 * __vfs_setxattr_noperm().  The caller of which has taken the inode's
 * i_mutex lock.
 */
void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
                             const void *xattr_value, size_t xattr_value_len)
{
        if (!evm_key_loaded() || (!evm_protected_xattr(xattr_name)
                                  && !posix_xattr_acl(xattr_name)))
                return;

        evm_reset_status(dentry->d_inode);

        evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
}

/**
 * evm_inode_post_removexattr - update 'security.evm' after removing the xattr
 * @dentry: pointer to the affected dentry
 * @xattr_name: pointer to the affected extended attribute name
 *
 * Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
 *
 * No need to take the i_mutex lock here, as this function is called from
 * vfs_removexattr() which takes the i_mutex.
 */
void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
{
        if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
                return;

        evm_reset_status(dentry->d_inode);

        evm_update_evmxattr(dentry, xattr_name, NULL, 0);
}

/**
 * evm_inode_setattr - prevent updating an invalid EVM extended attribute
 * @dentry: pointer to the affected dentry
 *
 * Permit update of file attributes when files have a valid EVM signature,
 * except in the case of them having an immutable portable signature.
 */
int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
{
        unsigned int ia_valid = attr->ia_valid;
        enum integrity_status evm_status;

        /* Policy permits modification of the protected attrs even though
         * there's no HMAC key loaded
         */
        if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
                return 0;

        if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
                return 0;
        evm_status = evm_verify_current_integrity(dentry);
        if ((evm_status == INTEGRITY_PASS) ||
            (evm_status == INTEGRITY_NOXATTRS))
                return 0;
        integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
                            dentry->d_name.name, "appraise_metadata",
                            integrity_status_msg[evm_status], -EPERM, 0);
        return -EPERM;
}

/**
 * evm_inode_post_setattr - update 'security.evm' after modifying metadata
 * @dentry: pointer to the affected dentry
 * @ia_valid: for the UID and GID status
 *
 * For now, update the HMAC stored in 'security.evm' to reflect UID/GID
 * changes.
 *
 * This function is called from notify_change(), which expects the caller
 * to lock the inode's i_mutex.
 */
void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
{
        if (!evm_key_loaded())
                return;

        if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
                evm_update_evmxattr(dentry, NULL, NULL, 0);
}

/*
 * evm_inode_init_security - initializes security.evm
 */
int evm_inode_init_security(struct inode *inode,
                                 const struct xattr *lsm_xattr,
                                 struct xattr *evm_xattr)
{
        struct evm_xattr *xattr_data;
        int rc;

        if (!evm_key_loaded() || !evm_protected_xattr(lsm_xattr->name))
                return 0;

        xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
        if (!xattr_data)
                return -ENOMEM;

        xattr_data->data.type = EVM_XATTR_HMAC;
        rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
        if (rc < 0)
                goto out;

        evm_xattr->value = xattr_data;
        evm_xattr->value_len = sizeof(*xattr_data);
        evm_xattr->name = XATTR_EVM_SUFFIX;
        return 0;
out:
        kfree(xattr_data);
        return rc;
}
EXPORT_SYMBOL_GPL(evm_inode_init_security);

#ifdef CONFIG_EVM_LOAD_X509
void __init evm_load_x509(void)
{
        int rc;

        rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
        if (!rc)
                evm_initialized |= EVM_INIT_X509;
}
#endif

static int __init init_evm(void)
{
        int error;
        struct list_head *pos, *q;

        evm_init_config();

        error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
        if (error)
                goto error;

        error = evm_init_secfs();
        if (error < 0) {
                pr_info("Error registering secfs\n");
                goto error;
        }

error:
        if (error != 0) {
                if (!list_empty(&evm_config_xattrnames)) {
                        list_for_each_safe(pos, q, &evm_config_xattrnames)
                                list_del(pos);
                }
        }

        return error;
}

late_initcall(init_evm);