path: root/libmount/src/hook_veritydev.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * This file is part of libmount from util-linux project.
 *
 * Copyright (C) 2019 Microsoft Corporation
 * Copyright (C) 2022 Karel Zak <kzak@redhat.com>
 *
 * libmount is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 *
 * Please, see comment in libmount/src/hooks.c to understand how hooks work.
 */
#include "mountP.h"

#ifdef HAVE_CRYPTSETUP

#include <libcryptsetup.h>
#include "path.h"
#include "strutils.h"
#include "fileutils.h"
#include "pathnames.h"

#ifdef CRYPTSETUP_VIA_DLOPEN
# include <dlfcn.h>

/* Pointers to libcryptsetup functions (initiliazed by dlsym()) */
struct verity_opers {
	void (*crypt_set_debug_level)(int);
	void (*crypt_set_log_callback)(struct crypt_device *, void (*log)(int, const char *, void *), void *);
	int (*crypt_init_data_device)(struct crypt_device **, const char *, const char *);
	int (*crypt_load)(struct crypt_device *, const char *, void *);
	int (*crypt_get_volume_key_size)(struct crypt_device *);
# ifdef HAVE_CRYPT_ACTIVATE_BY_SIGNED_KEY
	int (*crypt_activate_by_signed_key)(struct crypt_device *, const char *, const char *, size_t, const char *, size_t, uint32_t);
# endif
	int (*crypt_activate_by_volume_key)(struct crypt_device *, const char *, const char *, size_t, uint32_t);
	void (*crypt_free)(struct crypt_device *);
	int (*crypt_init_by_name)(struct crypt_device **, const char *);
	int (*crypt_get_verity_info)(struct crypt_device *, struct crypt_params_verity *);
	int (*crypt_volume_key_get)(struct crypt_device *, int, char *, size_t *, const char *, size_t);

	int (*crypt_deactivate_by_name)(struct crypt_device *, const char *, uint32_t);
};

/* libcryptsetup functions names and offsets in 'struct verity_opers' */
struct verity_sym {
	const char *name;
	size_t offset;		/* offset of the symbol in verity_opers */
};

# define DEF_VERITY_SYM(_name) \
	{ \
		.name = # _name, \
		.offset = offsetof(struct verity_opers, _name), \
	}

/* All required symbols */
static const struct verity_sym verity_symbols[] =
{
	DEF_VERITY_SYM( crypt_set_debug_level ),
	DEF_VERITY_SYM( crypt_set_log_callback ),
	DEF_VERITY_SYM( crypt_init_data_device ),
	DEF_VERITY_SYM( crypt_load ),
	DEF_VERITY_SYM( crypt_get_volume_key_size ),
# ifdef HAVE_CRYPT_ACTIVATE_BY_SIGNED_KEY
	DEF_VERITY_SYM( crypt_activate_by_signed_key ),
# endif
	DEF_VERITY_SYM( crypt_activate_by_volume_key ),
	DEF_VERITY_SYM( crypt_free ),
	DEF_VERITY_SYM( crypt_init_by_name ),
	DEF_VERITY_SYM( crypt_get_verity_info ),
	DEF_VERITY_SYM( crypt_volume_key_get ),

	DEF_VERITY_SYM( crypt_deactivate_by_name ),
};
#endif /* CRYPTSETUP_VIA_DLOPEN */


/* Data used by all verity hooks */
struct hookset_data {
	char *devname;			/* the device */
#ifdef CRYPTSETUP_VIA_DLOPEN
	void *dl;			/* dlopen() */
	struct verity_opers dl_funcs;	/* dlsym() */
#endif
};

/* libcryptsetup call -- dlopen version requires 'struct hookset_data *hsd' */
#ifdef CRYPTSETUP_VIA_DLOPEN
# define verity_call(_func)	(hsd->dl_funcs._func)
#else
# define verity_call(_func)	(_func)
#endif


static void delete_veritydev(struct libmnt_context *cxt,
                        const struct libmnt_hookset *hs,
                        struct hookset_data *hsd);


#ifdef CRYPTSETUP_VIA_DLOPEN
static int load_libcryptsetup_symbols(struct libmnt_context *cxt,
				      const struct libmnt_hookset *hs,
				      struct hookset_data *hsd)
{
	size_t i;
	int flags = RTLD_LAZY | RTLD_LOCAL;

	assert(cxt);
	assert(hsd);
	assert(hsd->dl == NULL);

	/* glibc extension: mnt_context_deferred_delete_veritydev is called immediately after, don't unload on dl_close */
#ifdef RTLD_NODELETE
	flags |= RTLD_NODELETE;
#endif
	/* glibc extension: might help to avoid further symbols clashes */
#ifdef RTLD_DEEPBIND
	flags |= RTLD_DEEPBIND;
#endif
	hsd->dl = dlopen("libcryptsetup.so.12", flags);
	if (!hsd->dl) {
		DBG(HOOK, ul_debugobj(hs, "cannot dlopen libcryptsetup"));
		return -ENOTSUP;
	}

	/* clear errors first, then load all the libcryptsetup symbols */
	dlerror();

	/* dlsym()  */
	for (i = 0; i < ARRAY_SIZE(verity_symbols); i++) {
		char *errmsg;
		const struct verity_sym *def = &verity_symbols[i];
		void **sym;

		sym = (void **) ((char *) (&hsd->dl_funcs) + def->offset);
		*sym = dlsym(hsd->dl, def->name);

		errmsg = dlerror();
		if (errmsg) {
			DBG(HOOK, ul_debugobj(hs, "dlsym failed %s: %s", def->name, errmsg));
			return -ENOTSUP;
		}
	}
	return 0;
}
#endif

/* libcryptsetup callback */
static void libcryptsetup_log(int level __attribute__((__unused__)),
			      const char *msg, void *data)
{
	const struct libmnt_hookset *hs = (struct libmnt_hookset *) data;
	DBG(HOOK, ul_debugobj(hs, "cryptsetup: %s", msg));
}

/* free global data */
static void free_hookset_data(	struct libmnt_context *cxt,
				const struct libmnt_hookset *hs)
{
	struct hookset_data *hsd = mnt_context_get_hookset_data(cxt, hs);

	if (!hsd)
		return;
	if (hsd->devname)
		delete_veritydev(cxt, hs, hsd);
#ifdef CRYPTSETUP_VIA_DLOPEN
	if (hsd->dl)
		dlclose(hsd->dl);
#endif
	free(hsd);
	mnt_context_set_hookset_data(cxt, hs, NULL);
}

/* global data, used by all callbacks */
static struct hookset_data *new_hookset_data(
				struct libmnt_context *cxt,
				const struct libmnt_hookset *hs)
{
	struct hookset_data *hsd = calloc(1, sizeof(struct hookset_data));

	if (hsd && mnt_context_set_hookset_data(cxt, hs, hsd) != 0)
		goto failed;

#ifdef CRYPTSETUP_VIA_DLOPEN
	if (load_libcryptsetup_symbols(cxt, hs, hsd) != 0)
		goto failed;
#endif
	if (mnt_context_is_verbose(cxt))
		verity_call( crypt_set_debug_level(CRYPT_DEBUG_ALL) );

	verity_call( crypt_set_log_callback(NULL, libcryptsetup_log, (void *) hs) );

	return hsd;
failed:
	free(hsd);
	return NULL;
}

/* libmount callback -- cleanup all */
static int hookset_deinit(struct libmnt_context *cxt, const struct libmnt_hookset *hs)
{
	DBG(HOOK, ul_debugobj(hs, "deinit '%s'", hs->name));

	/* remove all our hooks */
	while (mnt_context_remove_hook(cxt, hs, 0, NULL) == 0);

	/* free and remove global hookset data */
	free_hookset_data(cxt, hs);

	return 0;
}

/* check mount options for verity stuff */
static int is_veritydev_required(struct libmnt_context *cxt,
				 const struct libmnt_hookset *hs,
				 struct libmnt_optlist *ol)
{
	const char *src;
	unsigned long flags = 0;

	assert(cxt);
	assert((cxt->flags & MNT_FL_MOUNTFLAGS_MERGED));

	if (cxt->action != MNT_ACT_MOUNT)
		return 0;
	if (!cxt->fs)
		return 0;
	src = mnt_fs_get_srcpath(cxt->fs);
	if (!src)
		return 0;		/* backing file not set */

	ol = mnt_context_get_optlist(cxt);
	if (!ol)
		return 0;
	if (mnt_optlist_is_bind(ol)
	    || mnt_optlist_is_move(ol)
	    || mnt_context_propagation_only(cxt))
		return 0;

	if (mnt_context_get_user_mflags(cxt, &flags))
		return 0;

	if (flags & (MNT_MS_HASH_DEVICE | MNT_MS_ROOT_HASH | MNT_MS_HASH_OFFSET)) {
		DBG(HOOK, ul_debugobj(hs, "verity options detected"));
		return 1;
	}

	return 0;
}

static void delete_veritydev(struct libmnt_context *cxt,
			const struct libmnt_hookset *hs,
			struct hookset_data *hsd)
{
	uint32_t flags = 0;
	int rc;

	if (!hsd || !hsd->devname)
		return;

	if (mnt_context_get_status(cxt) != 0)
		/*
		 * mount(2) success, use deferred deactivation
		 */
		flags |= CRYPT_DEACTIVATE_DEFERRED;

	rc = verity_call( crypt_deactivate_by_name(NULL, hsd->devname, flags) );

	DBG(HOOK, ul_debugobj(hs, "deleted %s [rc=%d%s]",
				hsd->devname, rc,
				flags & CRYPT_DEACTIVATE_DEFERRED ? " deferred" : "" ));
	if (rc == 0) {
		free(hsd->devname);
		hsd->devname = NULL;
	}

	return;
}

/* Taken from https://gitlab.com/cryptsetup/cryptsetup/blob/master/lib/utils_crypt.c#L225 */
static size_t crypt_hex_to_bytes(const char *hex, char **result)
{
	char buf[3] = "xx\0", *endp, *bytes;
	size_t i, len;

	len = strlen(hex);
	if (len % 2)
		return -EINVAL;
	len /= 2;

	bytes = malloc(len);
	if (!bytes)
		return -ENOMEM;

	for (i = 0; i < len; i++) {
		memcpy(buf, &hex[i * 2], 2);
		errno = 0;
		bytes[i] = strtoul(buf, &endp, 16);
		if (errno || endp != &buf[2]) {
			free(bytes);
			return -EINVAL;
		}
	}
	*result = bytes;
	return i;
}


static int setup_veritydev(	struct libmnt_context *cxt,
				const struct libmnt_hookset *hs,
				struct hookset_data *hsd,
				struct libmnt_optlist *ol)
{
	struct libmnt_opt *opt;
	const char	*backing_file,
			*hash_device = NULL,
			*root_hash_file = NULL,
			*fec_device = NULL,
			*root_hash_sig_file = NULL;
	char		*key = NULL,
			*root_hash_binary = NULL,
			*mapper_device = NULL,
			*root_hash = NULL,
			*hash_sig = NULL;

	size_t hash_size, hash_sig_size = 0, keysize = 0;
	struct crypt_params_verity crypt_params = {};
	struct crypt_device *crypt_dev = NULL;

	int rc = 0;
	/* Use the same default for FEC parity bytes as cryptsetup uses */
	uint64_t offset = 0, fec_offset = 0, fec_roots = 2;
	uint32_t crypt_activate_flags = CRYPT_ACTIVATE_READONLY;

	struct stat hash_sig_st;

	assert(cxt);
	assert(cxt->fs);
	assert(hsd);
	assert(hsd->devname == NULL);

	/* dm-verity volumes are read-only, and mount will fail if not set */
	mnt_optlist_append_flags(ol, MS_RDONLY, cxt->map_linux);

	backing_file = mnt_fs_get_srcpath(cxt->fs);
	if (!backing_file)
		return -EINVAL;
	else {
		/* To avoid clashes, prefix libmnt_ to all mapper devices */
		char *p, *path = strdup(backing_file);
		if (!path)
			return -ENOMEM;

		p = stripoff_last_component(path);
		if (p)
			mapper_device = calloc(strlen(p) + sizeof("libmnt_"), sizeof(char));
		if (mapper_device) {
			strcat(mapper_device, "libmnt_");
			strcat(mapper_device, p);
		}
		free(path);
		if (!mapper_device)
			return -ENOMEM;
	}

	DBG(HOOK, ul_debugobj(hs, "verity: setup for %s [%s]", backing_file, mapper_device));

	/* verity.hashdevice= */
	if (!rc && (opt = mnt_optlist_get_opt(ol, MNT_MS_HASH_DEVICE, cxt->map_userspace)))
		hash_device = mnt_opt_get_value(opt);

	/* verity.roothash= */
	if (!rc && (opt = mnt_optlist_get_opt(ol, MNT_MS_ROOT_HASH, cxt->map_userspace))) {
		root_hash = strdup(mnt_opt_get_value(opt));
		rc = root_hash ? 0 : -ENOMEM;
	}

	/* verity.hashoffset= */
	if (!rc && (opt = mnt_optlist_get_opt(ol, MNT_MS_HASH_OFFSET, cxt->map_userspace))
	    && mnt_opt_has_value(opt)) {
		if (strtosize(mnt_opt_get_value(opt), &offset)) {
			DBG(HOOK, ul_debugobj(hs, "failed to parse verity.hashoffset="));
			rc = -MNT_ERR_MOUNTOPT;
		}
	}

	/* verity.roothashfile= */
	if (!rc && (opt = mnt_optlist_get_opt(ol, MNT_MS_ROOT_HASH_FILE, cxt->map_userspace)))
		root_hash_file = mnt_opt_get_value(opt);

	/* verity.fecdevice= */
	if (!rc && (opt = mnt_optlist_get_opt(ol, MNT_MS_FEC_DEVICE, cxt->map_userspace)))
		fec_device = mnt_opt_get_value(opt);

	/* verity.fecoffset= */
	if (!rc && (opt = mnt_optlist_get_opt(ol, MNT_MS_FEC_OFFSET, cxt->map_userspace))
	    && mnt_opt_has_value(opt)
	    && strtosize(mnt_opt_get_value(opt), &fec_offset)) {
		DBG(HOOK, ul_debugobj(hs, "failed to parse verity.fecoffset="));
		rc = -MNT_ERR_MOUNTOPT;
	}

	/* verity.fecroots=  */
	if (!rc && (opt = mnt_optlist_get_opt(ol, MNT_MS_FEC_ROOTS, cxt->map_userspace))
	    && mnt_opt_has_value(opt)
	    && strtosize(mnt_opt_get_value(opt), &fec_roots)) {
		DBG(HOOK, ul_debugobj(hs, "failed to parse verity.fecroots="));
		rc = -MNT_ERR_MOUNTOPT;
	}

	/* verity.roothashsig= */
	if (!rc && (opt = mnt_optlist_get_opt(ol, MNT_MS_ROOT_HASH_SIG, cxt->map_userspace))
	    && mnt_opt_has_value(opt)) {
		root_hash_sig_file = mnt_opt_get_value(opt);

		DBG(HOOK, ul_debugobj(hs, "verity: checking %s", root_hash_sig_file));

		rc = ul_path_stat(NULL, &hash_sig_st, 0, root_hash_sig_file);
		if (rc == 0)
			rc = S_ISREG(hash_sig_st.st_mode) && hash_sig_st.st_size ? 0 : -EINVAL;
		if (rc == 0) {
			hash_sig_size = hash_sig_st.st_size;
			hash_sig = malloc(hash_sig_size);
			rc = hash_sig ? 0 : -ENOMEM;
		}
		if (rc == 0) {
			rc = ul_path_read(NULL, hash_sig, hash_sig_size, root_hash_sig_file);
			rc = rc < (int)hash_sig_size ? -1 : 0;
		}
	}

	/* verity.oncorruption= */
	if (!rc && (opt = mnt_optlist_get_opt(ol, MNT_MS_VERITY_ON_CORRUPTION, cxt->map_userspace))
	    && mnt_opt_has_value(opt)) {
		const char *val =  mnt_opt_get_value(opt);
		if (!strcmp(val, "ignore"))
			crypt_activate_flags |= CRYPT_ACTIVATE_IGNORE_CORRUPTION;
		else if (!strcmp(val, "restart"))
			crypt_activate_flags |= CRYPT_ACTIVATE_RESTART_ON_CORRUPTION;
		else if (!strcmp(val, "panic"))
			/* Added by libcryptsetup v2.3.4 - ignore on lower versions, as with other optional features */
#ifdef CRYPT_ACTIVATE_PANIC_ON_CORRUPTION
			crypt_activate_flags |= CRYPT_ACTIVATE_PANIC_ON_CORRUPTION;
#else
			DBG(HOOK, ul_debugobj(hs, "verity.oncorruption=panic not supported by libcryptsetup, ignoring"));
#endif
		else {
			DBG(HOOK, ul_debugobj(hs, "failed to parse verity.oncorruption="));
			rc = -MNT_ERR_MOUNTOPT;
		}
	}

	if (!rc && root_hash && root_hash_file) {
		DBG(HOOK, ul_debugobj(hs, "verity.roothash and verity.roothashfile are mutually exclusive"));
		rc = -EINVAL;
	} else if (!rc && root_hash_file) {
		rc = ul_path_read_string(NULL, &root_hash, root_hash_file);
		rc = rc < 1 ? rc : 0;
	}

	if (!rc && (!hash_device || !root_hash)) {
		DBG(HOOK, ul_debugobj(hs, "verity.hashdevice and one of verity.roothash or verity.roothashfile are mandatory"));
		rc = -EINVAL;
	}

	if (!rc)
		rc = verity_call( crypt_init_data_device(&crypt_dev, hash_device, backing_file) );
	if (rc)
		goto done;

	memset(&crypt_params, 0, sizeof(struct crypt_params_verity));
	crypt_params.hash_area_offset = offset;
	crypt_params.fec_area_offset = fec_offset;
	crypt_params.fec_roots = fec_roots;
	crypt_params.fec_device = fec_device;
	crypt_params.flags = 0;

	rc = verity_call( crypt_load(crypt_dev, CRYPT_VERITY, &crypt_params) );
	if (rc < 0)
		goto done;

	hash_size = verity_call( crypt_get_volume_key_size(crypt_dev) );
	if (crypt_hex_to_bytes(root_hash, &root_hash_binary) != hash_size) {
		DBG(HOOK, ul_debugobj(hs, "root hash %s is not of length %zu", root_hash, hash_size));
		rc = -EINVAL;
		goto done;
	}

	if (hash_sig) {
#ifdef HAVE_CRYPT_ACTIVATE_BY_SIGNED_KEY
		rc = verity_call( crypt_activate_by_signed_key(crypt_dev, mapper_device, root_hash_binary, hash_size,
				hash_sig, hash_sig_size, crypt_activate_flags) );
#else
		rc = -EINVAL;
		DBG(HOOK, ul_debugobj(hs, "verity.roothashsig=%s passed but libcryptsetup does not provide crypt_activate_by_signed_key()", hash_sig));
#endif
	} else
		rc = verity_call( crypt_activate_by_volume_key(crypt_dev, mapper_device, root_hash_binary, hash_size,
				crypt_activate_flags) );

	/*
	 * If the mapper device already exists, and if libcryptsetup supports it, get the root
	 * hash associated with the existing one and compare it with the parameter passed by
	 * the user. If they match, then we can be sure the user intended to mount the exact
	 * same device, and simply reuse it and return success.
	 * The kernel does the refcounting for us.
	 * If libcryptsetup does not support getting the root hash out of an existing device,
	 * then return an error and tell the user that the device is already in use.
	 * Pass through only OOM errors or mismatching root hash errors.
	 */
	if (rc == -EEXIST) {
		DBG(HOOK, ul_debugobj(hs, "%s already in use as /dev/mapper/%s", backing_file, mapper_device));

		verity_call( crypt_free(crypt_dev) );

		rc = verity_call( crypt_init_by_name(&crypt_dev, mapper_device) );
		if (!rc) {
			rc = verity_call( crypt_get_verity_info(crypt_dev, &crypt_params) );
			if (!rc) {
				key = calloc(hash_size, 1);
				if (!key) {
					rc = -ENOMEM;
					goto done;
				}
			}
			if (!rc) {
				keysize = hash_size;
				rc = verity_call( crypt_volume_key_get(crypt_dev, CRYPT_ANY_SLOT, key, &keysize, NULL, 0) );
			}
			if (!rc) {
				DBG(HOOK, ul_debugobj(hs, "comparing root hash of existing device with %s", root_hash));
				if (memcmp(key, root_hash_binary, hash_size)) {
					DBG(HOOK, ul_debugobj(hs, "existing device's hash does not match with %s", root_hash));
					rc = -EINVAL;
					goto done;
				}
			} else {
				DBG(HOOK, ul_debugobj(hs, "libcryptsetup does not support extracting root hash of existing device"));
			}
		}
		if (rc) {
			rc = -EEXIST;
		} else {
			/*
			 * Ensure that, if signatures are supported, we only reuse the device if the previous mount
			 * used the same settings, so that a previous unsigned mount will not be reused if the user
			 * asks to use signing for the new one, and viceversa.
			 */
#ifdef HAVE_CRYPT_ACTIVATE_BY_SIGNED_KEY
			if (!!hash_sig != !!(crypt_params.flags & CRYPT_VERITY_ROOT_HASH_SIGNATURE)) {
				rc = -EINVAL;
				DBG(HOOK, ul_debugobj(hs, "existing device and new mount have to either be both opened with signature or both without"));
				goto done;
			}
#endif
			DBG(HOOK, ul_debugobj(hs, "root hash of %s matches %s, reusing device", mapper_device, root_hash));
		}
	}

	if (!rc) {
		hsd->devname = calloc(strlen(mapper_device)
					+ sizeof(_PATH_DEV_MAPPER) + 2, sizeof(char));
		if (!hsd->devname)
			rc = -ENOMEM;
		else {
			strcat(hsd->devname, _PATH_DEV_MAPPER "/");
			strcat(hsd->devname, mapper_device);
			rc = mnt_fs_set_source(cxt->fs, hsd->devname);
		}
	}

done:
	verity_call( crypt_free(crypt_dev) );

	free(root_hash_binary);
	free(mapper_device);
	free(root_hash);
	free(hash_sig);
	free(key);
	return rc;
}
/* call after mount(2) */
static int hook_mount_post(
			struct libmnt_context *cxt,
			const struct libmnt_hookset *hs,
			void *data __attribute__((__unused__)))
{

	delete_veritydev(cxt, hs, mnt_context_get_hookset_data(cxt, hs));
	return 0;
}

/*
 * first call (first callback in this hookset)
 */
static int hook_prepare_source(
                        struct libmnt_context *cxt,
                        const struct libmnt_hookset *hs,
                        void *data __attribute__((__unused__)))
{
	struct libmnt_optlist *ol;
	struct hookset_data *hsd;
	int rc;

	assert(cxt);

	ol = mnt_context_get_optlist(cxt);
	if (!ol)
		return -ENOMEM;

	if (!is_veritydev_required(cxt, hs, ol))
		return 0;

	hsd = new_hookset_data(cxt, hs);
	if (!hsd)
		return -ENOMEM;

	rc = setup_veritydev(cxt, hs, hsd, ol);
	if (!rc) {
		rc = mnt_context_append_hook(cxt, hs,
				MNT_STAGE_MOUNT_POST,
				NULL, hook_mount_post);
		if (rc)
			delete_veritydev(cxt, hs, hsd);
	}
	return rc;
}


const struct libmnt_hookset hookset_veritydev =
{
	.name = "__veritydev",

	.firststage = MNT_STAGE_PREP_SOURCE,
	.firstcall = hook_prepare_source,

	.deinit = hookset_deinit
};
#endif /*HAVE_CRYPTSETUP*/