// SPDX-License-Identifier: GPL-2.0
/*
 * Encryption policy functions for per-file encryption support.
 *
 * Copyright (C) 2015, Google, Inc.
 * Copyright (C) 2015, Motorola Mobility.
 *
 * Originally written by Michael Halcrow, 2015.
 * Modified by Jaegeuk Kim, 2015.
 * Modified by Eric Biggers, 2019 for v2 policy support.
 */

#include <linux/random.h>
#include <linux/string.h>
#include <linux/mount.h>
#include "fscrypt_private.h"

/**
 * fscrypt_policies_equal - check whether two encryption policies are the same
 *
 * Return: %true if equal, else %false
 */
bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
                            const union fscrypt_policy *policy2)
{
        if (policy1->version != policy2->version)
                return false;

        return !memcmp(policy1, policy2, fscrypt_policy_size(policy1));
}

static bool supported_iv_ino_lblk_64_policy(
                                        const struct fscrypt_policy_v2 *policy,
                                        const struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        int ino_bits = 64, lblk_bits = 64;

        if (policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
                fscrypt_warn(inode,
                             "The DIRECT_KEY and IV_INO_LBLK_64 flags are mutually exclusive");
                return false;
        }
        /*
         * It's unsafe to include inode numbers in the IVs if the filesystem can
         * potentially renumber inodes, e.g. via filesystem shrinking.
         */
        if (!sb->s_cop->has_stable_inodes ||
            !sb->s_cop->has_stable_inodes(sb)) {
                fscrypt_warn(inode,
                             "Can't use IV_INO_LBLK_64 policy on filesystem '%s' because it doesn't have stable inode numbers",
                             sb->s_id);
                return false;
        }
        if (sb->s_cop->get_ino_and_lblk_bits)
                sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits);
        if (ino_bits > 32 || lblk_bits > 32) {
                fscrypt_warn(inode,
                             "Can't use IV_INO_LBLK_64 policy on filesystem '%s' because it doesn't use 32-bit inode and block numbers",
                             sb->s_id);
                return false;
        }
        return true;
}

/**
 * fscrypt_supported_policy - check whether an encryption policy is supported
 *
 * Given an encryption policy, check whether all its encryption modes and other
 * settings are supported by this kernel.  (But we don't currently don't check
 * for crypto API support here, so attempting to use an algorithm not configured
 * into the crypto API will still fail later.)
 *
 * Return: %true if supported, else %false
 */
bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
                              const struct inode *inode)
{
        switch (policy_u->version) {
        case FSCRYPT_POLICY_V1: {
                const struct fscrypt_policy_v1 *policy = &policy_u->v1;

                if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
                                             policy->filenames_encryption_mode)) {
                        fscrypt_warn(inode,
                                     "Unsupported encryption modes (contents %d, filenames %d)",
                                     policy->contents_encryption_mode,
                                     policy->filenames_encryption_mode);
                        return false;
                }

                if (policy->flags & ~(FSCRYPT_POLICY_FLAGS_PAD_MASK |
                                      FSCRYPT_POLICY_FLAG_DIRECT_KEY)) {
                        fscrypt_warn(inode,
                                     "Unsupported encryption flags (0x%02x)",
                                     policy->flags);
                        return false;
                }

                return true;
        }
        case FSCRYPT_POLICY_V2: {
                const struct fscrypt_policy_v2 *policy = &policy_u->v2;

                if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode,
                                             policy->filenames_encryption_mode)) {
                        fscrypt_warn(inode,
                                     "Unsupported encryption modes (contents %d, filenames %d)",
                                     policy->contents_encryption_mode,
                                     policy->filenames_encryption_mode);
                        return false;
                }

                if (policy->flags & ~FSCRYPT_POLICY_FLAGS_VALID) {
                        fscrypt_warn(inode,
                                     "Unsupported encryption flags (0x%02x)",
                                     policy->flags);
                        return false;
                }

                if ((policy->flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) &&
                    !supported_iv_ino_lblk_64_policy(policy, inode))
                        return false;

                if (memchr_inv(policy->__reserved, 0,
                               sizeof(policy->__reserved))) {
                        fscrypt_warn(inode,
                                     "Reserved bits set in encryption policy");
                        return false;
                }

                return true;
        }
        }
        return false;
}

/**
 * fscrypt_new_context_from_policy - create a new fscrypt_context from a policy
 *
 * Create an fscrypt_context for an inode that is being assigned the given
 * encryption policy.  A new nonce is randomly generated.
 *
 * Return: the size of the new context in bytes.
 */
static int fscrypt_new_context_from_policy(union fscrypt_context *ctx_u,
                                           const union fscrypt_policy *policy_u)
{
        memset(ctx_u, 0, sizeof(*ctx_u));

        switch (policy_u->version) {
        case FSCRYPT_POLICY_V1: {
                const struct fscrypt_policy_v1 *policy = &policy_u->v1;
                struct fscrypt_context_v1 *ctx = &ctx_u->v1;

                ctx->version = FSCRYPT_CONTEXT_V1;
                ctx->contents_encryption_mode =
                        policy->contents_encryption_mode;
                ctx->filenames_encryption_mode =
                        policy->filenames_encryption_mode;
                ctx->flags = policy->flags;
                memcpy(ctx->master_key_descriptor,
                       policy->master_key_descriptor,
                       sizeof(ctx->master_key_descriptor));
                get_random_bytes(ctx->nonce, sizeof(ctx->nonce));
                return sizeof(*ctx);
        }
        case FSCRYPT_POLICY_V2: {
                const struct fscrypt_policy_v2 *policy = &policy_u->v2;
                struct fscrypt_context_v2 *ctx = &ctx_u->v2;

                ctx->version = FSCRYPT_CONTEXT_V2;
                ctx->contents_encryption_mode =
                        policy->contents_encryption_mode;
                ctx->filenames_encryption_mode =
                        policy->filenames_encryption_mode;
                ctx->flags = policy->flags;
                memcpy(ctx->master_key_identifier,
                       policy->master_key_identifier,
                       sizeof(ctx->master_key_identifier));
                get_random_bytes(ctx->nonce, sizeof(ctx->nonce));
                return sizeof(*ctx);
        }
        }
        BUG();
}

/**
 * fscrypt_policy_from_context - convert an fscrypt_context to an fscrypt_policy
 *
 * Given an fscrypt_context, build the corresponding fscrypt_policy.
 *
 * Return: 0 on success, or -EINVAL if the fscrypt_context has an unrecognized
 * version number or size.
 *
 * This does *not* validate the settings within the policy itself, e.g. the
 * modes, flags, and reserved bits.  Use fscrypt_supported_policy() for that.
 */
int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
                                const union fscrypt_context *ctx_u,
                                int ctx_size)
{
        memset(policy_u, 0, sizeof(*policy_u));

        if (ctx_size <= 0 || ctx_size != fscrypt_context_size(ctx_u))
                return -EINVAL;

        switch (ctx_u->version) {
        case FSCRYPT_CONTEXT_V1: {
                const struct fscrypt_context_v1 *ctx = &ctx_u->v1;
                struct fscrypt_policy_v1 *policy = &policy_u->v1;

                policy->version = FSCRYPT_POLICY_V1;
                policy->contents_encryption_mode =
                        ctx->contents_encryption_mode;
                policy->filenames_encryption_mode =
                        ctx->filenames_encryption_mode;
                policy->flags = ctx->flags;
                memcpy(policy->master_key_descriptor,
                       ctx->master_key_descriptor,
                       sizeof(policy->master_key_descriptor));
                return 0;
        }
        case FSCRYPT_CONTEXT_V2: {
                const struct fscrypt_context_v2 *ctx = &ctx_u->v2;
                struct fscrypt_policy_v2 *policy = &policy_u->v2;

                policy->version = FSCRYPT_POLICY_V2;
                policy->contents_encryption_mode =
                        ctx->contents_encryption_mode;
                policy->filenames_encryption_mode =
                        ctx->filenames_encryption_mode;
                policy->flags = ctx->flags;
                memcpy(policy->__reserved, ctx->__reserved,
                       sizeof(policy->__reserved));
                memcpy(policy->master_key_identifier,
                       ctx->master_key_identifier,
                       sizeof(policy->master_key_identifier));
                return 0;
        }
        }
        /* unreachable */
        return -EINVAL;
}

/* Retrieve an inode's encryption policy */
static int fscrypt_get_policy(struct inode *inode, union fscrypt_policy *policy)
{
        const struct fscrypt_info *ci;
        union fscrypt_context ctx;
        int ret;

        ci = READ_ONCE(inode->i_crypt_info);
        if (ci) {
                /* key available, use the cached policy */
                *policy = ci->ci_policy;
                return 0;
        }

        if (!IS_ENCRYPTED(inode))
                return -ENODATA;

        ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
        if (ret < 0)
                return (ret == -ERANGE) ? -EINVAL : ret;

        return fscrypt_policy_from_context(policy, &ctx, ret);
}

static int set_encryption_policy(struct inode *inode,
                                 const union fscrypt_policy *policy)
{
        union fscrypt_context ctx;
        int ctxsize;
        int err;

        if (!fscrypt_supported_policy(policy, inode))
                return -EINVAL;

        switch (policy->version) {
        case FSCRYPT_POLICY_V1:
                /*
                 * The original encryption policy version provided no way of
                 * verifying that the correct master key was supplied, which was
                 * insecure in scenarios where multiple users have access to the
                 * same encrypted files (even just read-only access).  The new
                 * encryption policy version fixes this and also implies use of
                 * an improved key derivation function and allows non-root users
                 * to securely remove keys.  So as long as compatibility with
                 * old kernels isn't required, it is recommended to use the new
                 * policy version for all new encrypted directories.
                 */
                pr_warn_once("%s (pid %d) is setting deprecated v1 encryption policy; recommend upgrading to v2.\n",
                             current->comm, current->pid);
                break;
        case FSCRYPT_POLICY_V2:
                err = fscrypt_verify_key_added(inode->i_sb,
                                               policy->v2.master_key_identifier);
                if (err)
                        return err;
                break;
        default:
                WARN_ON(1);
                return -EINVAL;
        }

        ctxsize = fscrypt_new_context_from_policy(&ctx, policy);

        return inode->i_sb->s_cop->set_context(inode, &ctx, ctxsize, NULL);
}

int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
{
        union fscrypt_policy policy;
        union fscrypt_policy existing_policy;
        struct inode *inode = file_inode(filp);
        u8 version;
        int size;
        int ret;

        if (get_user(policy.version, (const u8 __user *)arg))
                return -EFAULT;

        size = fscrypt_policy_size(&policy);
        if (size <= 0)
                return -EINVAL;

        /*
         * We should just copy the remaining 'size - 1' bytes here, but a
         * bizarre bug in gcc 7 and earlier (fixed by gcc r255731) causes gcc to
         * think that size can be 0 here (despite the check above!) *and* that
         * it's a compile-time constant.  Thus it would think copy_from_user()
         * is passed compile-time constant ULONG_MAX, causing the compile-time
         * buffer overflow check to fail, breaking the build. This only occurred
         * when building an i386 kernel with -Os and branch profiling enabled.
         *
         * Work around it by just copying the first byte again...
         */
        version = policy.version;
        if (copy_from_user(&policy, arg, size))
                return -EFAULT;
        policy.version = version;

        if (!inode_owner_or_capable(inode))
                return -EACCES;

        ret = mnt_want_write_file(filp);
        if (ret)
                return ret;

        inode_lock(inode);

        ret = fscrypt_get_policy(inode, &existing_policy);
        if (ret == -ENODATA) {
                if (!S_ISDIR(inode->i_mode))
                        ret = -ENOTDIR;
                else if (IS_DEADDIR(inode))
                        ret = -ENOENT;
                else if (!inode->i_sb->s_cop->empty_dir(inode))
                        ret = -ENOTEMPTY;
                else
                        ret = set_encryption_policy(inode, &policy);
        } else if (ret == -EINVAL ||
                   (ret == 0 && !fscrypt_policies_equal(&policy,
                                                        &existing_policy))) {
                /* The file already uses a different encryption policy. */
                ret = -EEXIST;
        }

        inode_unlock(inode);

        mnt_drop_write_file(filp);
        return ret;
}
EXPORT_SYMBOL(fscrypt_ioctl_set_policy);

/* Original ioctl version; can only get the original policy version */
int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
{
        union fscrypt_policy policy;
        int err;

        err = fscrypt_get_policy(file_inode(filp), &policy);
        if (err)
                return err;

        if (policy.version != FSCRYPT_POLICY_V1)
                return -EINVAL;

        if (copy_to_user(arg, &policy, sizeof(policy.v1)))
                return -EFAULT;
        return 0;
}
EXPORT_SYMBOL(fscrypt_ioctl_get_policy);

/* Extended ioctl version; can get policies of any version */
int fscrypt_ioctl_get_policy_ex(struct file *filp, void __user *uarg)
{
        struct fscrypt_get_policy_ex_arg arg;
        union fscrypt_policy *policy = (union fscrypt_policy *)&arg.policy;
        size_t policy_size;
        int err;

        /* arg is policy_size, then policy */
        BUILD_BUG_ON(offsetof(typeof(arg), policy_size) != 0);
        BUILD_BUG_ON(offsetofend(typeof(arg), policy_size) !=
                     offsetof(typeof(arg), policy));
        BUILD_BUG_ON(sizeof(arg.policy) != sizeof(*policy));

        err = fscrypt_get_policy(file_inode(filp), policy);
        if (err)
                return err;
        policy_size = fscrypt_policy_size(policy);

        if (copy_from_user(&arg, uarg, sizeof(arg.policy_size)))
                return -EFAULT;

        if (policy_size > arg.policy_size)
                return -EOVERFLOW;
        arg.policy_size = policy_size;

        if (copy_to_user(uarg, &arg, sizeof(arg.policy_size) + policy_size))
                return -EFAULT;
        return 0;
}
EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_policy_ex);

/**
 * fscrypt_has_permitted_context() - is a file's encryption policy permitted
 *                                   within its directory?
 *
 * @parent: inode for parent directory
 * @child: inode for file being looked up, opened, or linked into @parent
 *
 * Filesystems must call this before permitting access to an inode in a
 * situation where the parent directory is encrypted (either before allowing
 * ->lookup() to succeed, or for a regular file before allowing it to be opened)
 * and before any operation that involves linking an inode into an encrypted
 * directory, including link, rename, and cross rename.  It enforces the
 * constraint that within a given encrypted directory tree, all files use the
 * same encryption policy.  The pre-access check is needed to detect potentially
 * malicious offline violations of this constraint, while the link and rename
 * checks are needed to prevent online violations of this constraint.
 *
 * Return: 1 if permitted, 0 if forbidden.
 */
int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
{
        union fscrypt_policy parent_policy, child_policy;
        int err;

        /* No restrictions on file types which are never encrypted */
        if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
            !S_ISLNK(child->i_mode))
                return 1;

        /* No restrictions if the parent directory is unencrypted */
        if (!IS_ENCRYPTED(parent))
                return 1;

        /* Encrypted directories must not contain unencrypted files */
        if (!IS_ENCRYPTED(child))
                return 0;

        /*
         * Both parent and child are encrypted, so verify they use the same
         * encryption policy.  Compare the fscrypt_info structs if the keys are
         * available, otherwise retrieve and compare the fscrypt_contexts.
         *
         * Note that the fscrypt_context retrieval will be required frequently
         * when accessing an encrypted directory tree without the key.
         * Performance-wise this is not a big deal because we already don't
         * really optimize for file access without the key (to the extent that
         * such access is even possible), given that any attempted access
         * already causes a fscrypt_context retrieval and keyring search.
         *
         * In any case, if an unexpected error occurs, fall back to "forbidden".
         */

        err = fscrypt_get_encryption_info(parent);
        if (err)
                return 0;
        err = fscrypt_get_encryption_info(child);
        if (err)
                return 0;

        err = fscrypt_get_policy(parent, &parent_policy);
        if (err)
                return 0;

        err = fscrypt_get_policy(child, &child_policy);
        if (err)
                return 0;

        return fscrypt_policies_equal(&parent_policy, &child_policy);
}
EXPORT_SYMBOL(fscrypt_has_permitted_context);

/**
 * fscrypt_inherit_context() - Sets a child context from its parent
 * @parent: Parent inode from which the context is inherited.
 * @child:  Child inode that inherits the context from @parent.
 * @fs_data:  private data given by FS.
 * @preload:  preload child i_crypt_info if true
 *
 * Return: 0 on success, -errno on failure
 */
int fscrypt_inherit_context(struct inode *parent, struct inode *child,
                                                void *fs_data, bool preload)
{
        union fscrypt_context ctx;
        int ctxsize;
        struct fscrypt_info *ci;
        int res;

        res = fscrypt_get_encryption_info(parent);
        if (res < 0)
                return res;

        ci = READ_ONCE(parent->i_crypt_info);
        if (ci == NULL)
                return -ENOKEY;

        ctxsize = fscrypt_new_context_from_policy(&ctx, &ci->ci_policy);

        BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE);
        res = parent->i_sb->s_cop->set_context(child, &ctx, ctxsize, fs_data);
        if (res)
                return res;
        return preload ? fscrypt_get_encryption_info(child): 0;
}
EXPORT_SYMBOL(fscrypt_inherit_context);