apk-tools/src/extract_v2.c

/* extract_v2.c - Alpine Package Keeper (APK)
 *
 * Copyright (C) 2005-2008 Natanael Copa <n@tanael.org>
 * Copyright (C) 2008-2011 Timo Teräs <timo.teras@iki.fi>
 * All rights reserved.
 *
 * SPDX-License-Identifier: GPL-2.0-only
 */

#include "apk_context.h"
#include "apk_crypto.h"
#include "apk_extract.h"
#include "apk_package.h"
#include "apk_tar.h"

#define APK_SIGN_NONE                0
#define APK_SIGN_VERIFY              1
#define APK_SIGN_VERIFY_IDENTITY     2
#define APK_SIGN_GENERATE            4
#define APK_SIGN_VERIFY_AND_GENERATE 5

struct apk_sign_ctx {
	struct apk_trust *trust;
	int action;
	int num_signatures;
	int control_started : 1;
	int data_started : 1;
	int has_data_checksum : 1;
	int control_verified : 1;
	int data_verified : 1;
	int allow_untrusted : 1;
	char data_checksum[APK_DIGEST_MAX_LENGTH];

	struct apk_checksum identity;
	struct apk_digest_ctx digest_ctx;

	struct {
		struct apk_public_key *public_key;
		apk_blob_t data;
		uint16_t type;
		char *identity;
	} signature;
};

static void
    apk_sign_ctx_init(struct apk_sign_ctx *ctx, int action, struct apk_checksum *identity, struct apk_trust *trust)
{
	uint8_t digest_alg;

	memset(ctx, 0, sizeof(struct apk_sign_ctx));
	ctx->trust           = trust;
	ctx->action          = action;
	ctx->allow_untrusted = trust->allow_untrusted;

	switch (action) {
	case APK_SIGN_VERIFY:
		/* If we're only verifing, we're going to start with a
		 * signature section, which we don't need a hash of */
		digest_alg = APK_DIGEST_NONE;
		break;
	case APK_SIGN_VERIFY_IDENTITY:
		/* If we're checking the package against a particular hash,
		 * we need to start with that hash, because there may not
		 * be a signature section to deduce it from */
		digest_alg = APK_DIGEST_SHA1;
		memcpy(&ctx->identity, identity, sizeof(ctx->identity));
		break;
	case APK_SIGN_GENERATE:
	case APK_SIGN_VERIFY_AND_GENERATE:
		digest_alg = APK_DIGEST_SHA1;
		break;
	default:
		ctx->action          = APK_SIGN_NONE;
		ctx->control_started = 1;
		ctx->data_started    = 1;

		digest_alg = APK_DIGEST_NONE;
		break;
	}

	apk_digest_ctx_init(&ctx->digest_ctx, digest_alg);
}

static void apk_sign_ctx_free(struct apk_sign_ctx *ctx)
{
	if (ctx->signature.data.ptr != NULL) {
		free(ctx->signature.data.ptr);
	}

	apk_public_key_free(ctx->signature.public_key);
}

static int check_signing_key_trust(struct apk_sign_ctx *sctx)
{
	switch (sctx->action) {
	case APK_SIGN_VERIFY:
	case APK_SIGN_VERIFY_AND_GENERATE:
		if (sctx->signature.public_key == NULL) {
			if (sctx->allow_untrusted) {
				break;
			}
			return -APKE_SIGNATURE_UNTRUSTED;
		}
	}
	return 0;
}

static int apk_sign_ctx_process_file(struct apk_sign_ctx *ctx, const struct apk_file_info *fi, struct apk_istream *is)
{
	static struct {
		char type[8];
		uint8_t alg;
	} signature_type[] = {
	    {"RSA256", APK_SIGNATURE_RSA256},
	    {"RSA512", APK_SIGNATURE_RSA512},
	    {"CUTE", APK_SIGNATURE_CUTE},
	    {"RSA", APK_SIGNATURE_RSA},
	};

	uint16_t signature_alg = APK_SIGNATURE_MAX;
	struct apk_public_key *public_key;
	const char *name = NULL;
	int r, i;

	if (ctx->data_started) {
		return 1;
	}

	if (fi->name[0] != '.' || strchr(fi->name, '/') != NULL) {
		/* APKv1.0 compatibility - first non-hidden file is
		 * considered to start the data section of the file.
		 * This does not make any sense if the file has v2.0
		 * style .PKGINFO */
		if (ctx->has_data_checksum) {
			return -APKE_V2PKG_FORMAT;
		}
		/* Error out early if identity part is missing */
		if (ctx->action == APK_SIGN_VERIFY_IDENTITY) {
			return -APKE_V2PKG_FORMAT;
		}
		ctx->data_started    = 1;
		ctx->control_started = 1;

		r = check_signing_key_trust(ctx);
		if (r < 0) {
			return r;
		}

		return 1;
	}

	if (ctx->control_started) {
		return 1;
	}

	if (strncmp(fi->name, ".SIGN.", 6) != 0) {
		ctx->control_started = 1;
		return 1;
	}

	/* By this point, we must be handling a signature file */
	ctx->num_signatures++;

	/* Already found a signature by a trusted key; no need to keep searching */
	if ((ctx->action != APK_SIGN_VERIFY && ctx->action != APK_SIGN_VERIFY_AND_GENERATE)
	    || ctx->signature.public_key != NULL)
		return 0;

	for (i = 0; i < ARRAY_SIZE(signature_type); i++) {
		size_t slen = strlen(signature_type[i].type);
		if (strncmp(&fi->name[6], signature_type[i].type, slen) == 0 && fi->name[6 + slen] == '.') {
			signature_alg = signature_type[i].alg;
			name          = &fi->name[6 + slen + 1];
			break;
		}
	}

	if (signature_alg == APK_SIGNATURE_MAX) {
		return 0;
	}

	public_key = apk_trust_public_key_by_name(ctx->trust, name);
	if (public_key != NULL) {
		ctx->signature.public_key = public_key;
		ctx->signature.type       = signature_alg;
		ctx->signature.data       = apk_blob_from_istream(is, fi->size);
	}

	// TODO: check if its really a good idea to reset here
	apk_verify_digest_start(&ctx->digest_ctx, signature_alg);

	return 0;
}

/*	apk_sign_ctx_mpart_cb() handles hashing archives and checking signatures, but
	it can't do it alone. apk_sign_ctx_process_file() must be in the loop to
	actually select which signature is to be verified and load the corresponding
	public key into the context object, and	apk_sign_ctx_parse_pkginfo_line()
	needs to be called when handling the .PKGINFO file to find any applicable
	datahash and load it into the context for this function to check against. */
static int apk_sign_ctx_mpart_cb(void *ctx, int part, apk_blob_t data)
{
	struct apk_sign_ctx *sctx = (struct apk_sign_ctx *) ctx;
	struct apk_digest digest;
	int r, end_of_control;

	if ((part == APK_MPART_DATA) || (part == APK_MPART_BOUNDARY && sctx->data_started)) {
		goto update_digest;
	}

	/* Still in signature blocks? */
	if (!sctx->control_started) {
		if (part == APK_MPART_END) {
			return -APKE_V2PKG_FORMAT;
		}
		goto reset_digest;
	}

	/* Grab state and mark all remaining block as data */
	end_of_control     = (sctx->data_started == 0);
	sctx->data_started = 1;

	/* End of control-block and control does not have data checksum? */
	if (sctx->has_data_checksum == 0 && end_of_control && part != APK_MPART_END)
		goto update_digest;

	/* Drool in the remainder of the digest block now, we will finish
	 * hashing it in all cases */
	apk_digest_ctx_update(&sctx->digest_ctx, data.ptr, data.len);

	if (sctx->has_data_checksum && !end_of_control) {
		/* End of data-block with a checksum read from the control block */
		apk_digest_ctx_final(&sctx->digest_ctx, &digest);
		if (digest.len == 0 || memcmp(digest.data, sctx->data_checksum, digest.len) != 0) {
			return -APKE_V2PKG_INTEGRITY;
		}
		sctx->data_verified = 1;
		if (!sctx->allow_untrusted && !sctx->control_verified) {
			return -APKE_SIGNATURE_UNTRUSTED;
		}
		return 0;
	}

	/* Either end of control block with a data checksum or end
	 * of the data block following a control block without a data
	 * checksum. In either case, we're checking a signature. */
	r = check_signing_key_trust(sctx);
	if (r < 0)
		return r;

	switch (sctx->action) {
	case APK_SIGN_VERIFY:
	case APK_SIGN_VERIFY_AND_GENERATE:
		if (sctx->signature.public_key != NULL) {
			r = apk_verify(sctx->signature.public_key,
			               &sctx->digest_ctx,
			               sctx->signature.data.ptr,
			               sctx->signature.data.len);
			if (r != 0 && !sctx->allow_untrusted) {
				return -APKE_SIGNATURE_INVALID;
			}
		} else {
			r = 0;
			if (!sctx->allow_untrusted) {
				return -APKE_SIGNATURE_UNTRUSTED;
			}
		}
		if (r == 1) {
			sctx->control_verified = 1;
			if (!sctx->has_data_checksum && part == APK_MPART_END) {
				sctx->data_verified = 1;
			}
		}
		if (sctx->action == APK_SIGN_VERIFY_AND_GENERATE) {
			goto generate_identity;
		}
		break;
	case APK_SIGN_VERIFY_IDENTITY:
		/* Reset digest for hashing data */
		apk_digest_ctx_final(&sctx->digest_ctx, &digest);
		if (memcmp(digest.data, sctx->identity.data, sctx->identity.type) != 0) {
			return -APKE_V2PKG_INTEGRITY;
		}

		sctx->control_verified = 1;
		if (!sctx->has_data_checksum && part == APK_MPART_END) {
			sctx->data_verified = 1;
		}
		break;
	case APK_SIGN_GENERATE:
generate_identity:
		/* Package identity is the checksum */
		sctx->identity.type = apk_digest_alg_len(sctx->digest_ctx.alg);
		apk_digest_ctx_final(&sctx->digest_ctx, &digest);
		memcpy(sctx->identity.data, digest.data, sctx->identity.type);
		if (!sctx->has_data_checksum) {
			return -APKE_V2PKG_FORMAT;
		}
		break;
	}

reset_digest:
	apk_digest_ctx_reset(&sctx->digest_ctx, sctx->digest_ctx.alg);
	return 0;

update_digest:
	apk_digest_ctx_update(&sctx->digest_ctx, data.ptr, data.len);
	return 0;
}

static int apk_extract_verify_v2index(struct apk_extract_ctx *ectx, apk_blob_t *desc, struct apk_istream *is)
{
	return 0;
}

static int
    apk_extract_verify_v2file(struct apk_extract_ctx *ectx, const struct apk_file_info *fi, struct apk_istream *is)
{
	return 0;
}

static const struct apk_extract_ops extract_v2verify_ops = {
    .v2index = apk_extract_verify_v2index,
    .v2meta  = apk_extract_v2_meta,
    .file    = apk_extract_verify_v2file,
};

static int apk_extract_v2_entry(void *pctx, const struct apk_file_info *fi, struct apk_istream *is)
{
	struct apk_extract_ctx *ectx = pctx;
	struct apk_sign_ctx *sctx    = ectx->pctx;
	int r, type;

	r = apk_sign_ctx_process_file(sctx, fi, is);
	if (r <= 0)
		return r;

	if (!sctx->control_started)
		return 0;
	if (!sctx->data_started || !sctx->has_data_checksum) {
		if (fi->name[0] == '.') {
			ectx->is_package = 1;
			if (ectx->is_index) {
				return -APKE_V2NDX_FORMAT;
			}
			if (!ectx->ops->v2meta) {
				return -APKE_FORMAT_NOT_SUPPORTED;
			}
			if (strcmp(fi->name, ".PKGINFO") == 0) {
				return ectx->ops->v2meta(ectx, is);
			} else if (strcmp(fi->name, ".INSTALL") == 0) {
				return -APKE_V2PKG_FORMAT;
			} else if ((type = apk_script_type(&fi->name[1])) != APK_SCRIPT_INVALID) {
				if (ectx->ops->script) {
					return ectx->ops->script(ectx, type, fi->size, is);
				}
			}
		} else {
			ectx->is_index = 1;
			if (ectx->is_package) {
				return -APKE_V2PKG_FORMAT;
			}
			if (!ectx->ops->v2index) {
				return -APKE_FORMAT_NOT_SUPPORTED;
			}
			if (strcmp(fi->name, "DESCRIPTION") == 0) {
				free(ectx->desc.ptr);
				ectx->desc = apk_blob_from_istream(is, fi->size);
			} else if (strcmp(fi->name, "APKINDEX") == 0) {
				return ectx->ops->v2index(ectx, &ectx->desc, is);
			}
		}
		return 0;
	}

	if (!sctx->data_started)
		return 0;
	if (!ectx->ops->file)
		return -ECANCELED;
	return ectx->ops->file(ectx, fi, is);
}

int apk_extract_v2(struct apk_extract_ctx *ectx, struct apk_istream *is)
{
	struct apk_ctx *ac      = ectx->ac;
	struct apk_trust *trust = apk_ctx_get_trust(ac);
	struct apk_sign_ctx sctx;
	int r, action;

	if (ectx->generate_identity) {
		action = trust->allow_untrusted ? APK_SIGN_GENERATE : APK_SIGN_VERIFY_AND_GENERATE;
	} else if (ectx->identity) {
		action = APK_SIGN_VERIFY_IDENTITY;
	} else {
		action = APK_SIGN_VERIFY;
	}

	if (!ectx->ops) {
		ectx->ops = &extract_v2verify_ops;
	}

	ectx->pctx = &sctx;
	apk_sign_ctx_init(&sctx, action, ectx->identity, trust);
	r = apk_tar_parse(apk_istream_gunzip_mpart(is, apk_sign_ctx_mpart_cb, &sctx),
	                  apk_extract_v2_entry,
	                  ectx,
	                  apk_ctx_get_id_cache(ac));
	if (r == -ECANCELED) {
		r = 0;
	}
	if ((r == 0 || r == -APKE_EOF) && !ectx->is_package && !ectx->is_index) {
		r = ectx->ops->v2index ? -APKE_V2NDX_FORMAT : -APKE_V2PKG_FORMAT;
	}
	if (ectx->generate_identity) {
		*ectx->identity = sctx.identity;
	}
	apk_sign_ctx_free(&sctx);
	free(ectx->desc.ptr);
	apk_extract_reset(ectx);

	return r;
}

void apk_extract_v2_control(struct apk_extract_ctx *ectx, apk_blob_t l, apk_blob_t r)
{
	struct apk_sign_ctx *sctx = ectx->pctx;

	if (!sctx || !sctx->control_started || sctx->data_started) {
		return;
	}

	// TODO check if reset is ok
	if (apk_blob_compare(APK_BLOB_STR("datahash"), l) == 0) {
		sctx->has_data_checksum = 1;
		apk_digest_ctx_reset(&sctx->digest_ctx, APK_DIGEST_SHA256);
		apk_blob_pull_hexdump(&r, APK_BLOB_PTR_LEN(sctx->data_checksum, apk_digest_alg_len(APK_DIGEST_SHA256)));
	}
}

int apk_extract_v2_meta(struct apk_extract_ctx *ectx, struct apk_istream *is)
{
	apk_blob_t k, v, token = APK_BLOB_STRLIT("\n");
	while (apk_istream_get_delim(is, token, &k) == 0) {
		if (k.len < 1 || k.ptr[0] == '#') {
			continue;
		}

		if (apk_blob_split(k, APK_BLOB_STRLIT(" = "), &k, &v)) {
			apk_extract_v2_control(ectx, k, v);
		}
	}
	return 0;
}