rework unpacking of packages and harden package file format requirements

A crafted .apk file could to trick apk writing unverified data to
an unexpected file during temporary file creation due to bugs in handling
long link target name and the way a regular file is extracted.

Several hardening steps are implemented to avoid this:
 - the temporary file is now always first unlinked (apk thus reserved
   all filenames .apk.* to be it's working files)
 - the temporary file is after that created with O_EXCL to avoid races
 - the temporary file is no longer directly the archive entry name
   and thus directly controlled by potentially untrusted data
 - long file names and link target names are now rejected
 - hard link targets are now more rigorously checked
 - various additional checks added for the extraction process to
   error out early in case of malformed (or old legacy) file

Reported-by: Max Justicz <max@justi.cz>

Author: fabled

src/apk_archive.h

@@ -28,7 +28,8 @@ int apk_tar_write_entry(struct apk_ostream *, const struct apk_file_info *ae,
 int apk_tar_write_padding(struct apk_ostream *, const struct apk_file_info *ae);
 
 int apk_archive_entry_extract(int atfd, const struct apk_file_info *ae,
-			      const char *suffix, struct apk_istream *is,
+			      const char *extract_name, const char *hardlink_name,
+			      struct apk_istream *is,
 			      apk_progress_cb cb, void *cb_ctx);
 
 #endif

src/archive.c

@@ -317,6 +317,12 @@ int apk_tar_parse(struct apk_istream *is, apk_archive_entry_parser parser,
 			break;
 		}
 
+		if (strnlen(entry.name, PATH_MAX) >= PATH_MAX-10 ||
+		    (entry.link_target && strnlen(entry.link_target, PATH_MAX) >= PATH_MAX-10)) {
+			r = -ENAMETOOLONG;
+			goto err;
+		}
+
 		teis.bytes_left = entry.size;
 		if (entry.mode & S_IFMT) {
 			/* callback parser function */
@@ -428,23 +434,15 @@ int apk_tar_write_padding(struct apk_ostream *os, const struct apk_file_info *ae
 }
 
 int apk_archive_entry_extract(int atfd, const struct apk_file_info *ae,
-			      const char *suffix, struct apk_istream *is,
+			      const char *extract_name, const char *link_target,
+			      struct apk_istream *is,
 			      apk_progress_cb cb, void *cb_ctx)
 {
 	struct apk_xattr *xattr;
-	char *fn = ae->name;
+	const char *fn = extract_name ?: ae->name;
 	int fd, r = -1, atflags = 0, ret = 0;
 
-	if (suffix != NULL) {
-		fn = alloca(PATH_MAX);
-		snprintf(fn, PATH_MAX, "%s%s", ae->name, suffix);
-	}
-
-	if ((!S_ISDIR(ae->mode) && !S_ISREG(ae->mode)) ||
-	    (ae->link_target != NULL)) {
-		/* non-standard entries need to be deleted first */
-		unlinkat(atfd, fn, 0);
-	}
+	if (unlinkat(atfd, fn, 0) != 0 && errno != ENOENT) return -errno;
 
 	switch (ae->mode & S_IFMT) {
 	case S_IFDIR:
@@ -454,7 +452,7 @@ int apk_archive_entry_extract(int atfd, const struct apk_file_info *ae,
 		break;
 	case S_IFREG:
 		if (ae->link_target == NULL) {
-			int flags = O_RDWR | O_CREAT | O_TRUNC | O_CLOEXEC;
+			int flags = O_RDWR | O_CREAT | O_TRUNC | O_CLOEXEC | O_EXCL;
 
 			fd = openat(atfd, fn, flags, ae->mode & 07777);
 			if (fd < 0) {
@@ -465,18 +463,12 @@ int apk_archive_entry_extract(int atfd, const struct apk_file_info *ae,
 			if (r != ae->size) ret = r < 0 ? r : -ENOSPC;
 			close(fd);
 		} else {
-			char *link_target = ae->link_target;
-			if (suffix != NULL) {
-				link_target = alloca(PATH_MAX);
-				snprintf(link_target, PATH_MAX, "%s%s",
-					 ae->link_target, suffix);
-			}
-			r = linkat(atfd, link_target, atfd, fn, 0);
+			r = linkat(atfd, link_target ?: ae->link_target, atfd, fn, 0);
 			if (r < 0) ret = -errno;
 		}
 		break;
 	case S_IFLNK:
-		r = symlinkat(ae->link_target, atfd, fn);
+		r = symlinkat(link_target ?: ae->link_target, atfd, fn);
 		if (r < 0) ret = -errno;
 		atflags |= AT_SYMLINK_NOFOLLOW;
 		break;

src/commit.c

@@ -232,8 +232,8 @@ static int run_commit_hook(void *ctx, int dirfd, const char *file)
 	struct apk_database *db = hook->db;
 	char fn[PATH_MAX], *argv[] = { fn, (char *) commit_hook_str[hook->type], NULL };
 
-	if ((apk_flags & (APK_NO_SCRIPTS | APK_SIMULATE)) != 0)
-		return 0;
+	if (file[0] == '.') return 0;
+	if ((apk_flags & (APK_NO_SCRIPTS | APK_SIMULATE)) != 0) return 0;
 
 	snprintf(fn, sizeof(fn), "etc/apk/commit_hooks.d" "/%s", file);
 	if ((apk_flags & APK_NO_COMMIT_HOOKS) != 0) {

src/database.c

@@ -828,8 +828,9 @@ int apk_db_index_read(struct apk_database *db, struct apk_bstream *bs, int repo)
 		case 'F':
 			if (diri) apk_db_dir_apply_diri_permissions(diri);
 			if (pkg->name == NULL) goto bad_entry;
-			diri = apk_db_diri_new(db, pkg, l, &diri_node);
-			file_diri_node = &diri->owned_files.first;
+			diri = find_diri(ipkg, l, NULL, &diri_node);
+			if (!diri) diri = apk_db_diri_new(db, pkg, l, &diri_node);
+			file_diri_node = hlist_tail_ptr(&diri->owned_files);
 			break;
 		case 'a':
 			if (file == NULL) goto bad_entry;
@@ -2358,6 +2359,31 @@ static struct apk_db_dir_instance *apk_db_install_directory_entry(struct install
 	return diri;
 }
 
+#define TMPNAME_MAX	(PATH_MAX + 64)
+
+static const char *format_tmpname(struct apk_package *pkg, struct apk_db_file *f, char tmpname[static TMPNAME_MAX])
+{
+	EVP_MD_CTX mdctx;
+	unsigned char md[EVP_MAX_MD_SIZE];
+	apk_blob_t b = APK_BLOB_PTR_LEN(tmpname, TMPNAME_MAX);
+
+	if (!f) return NULL;
+
+	EVP_DigestInit(&mdctx, EVP_sha256());
+	EVP_DigestUpdate(&mdctx, pkg->name->name, strlen(pkg->name->name) + 1);
+	EVP_DigestUpdate(&mdctx, f->diri->dir->name, f->diri->dir->namelen);
+	EVP_DigestUpdate(&mdctx, "/", 1);
+	EVP_DigestUpdate(&mdctx, f->name, f->namelen);
+	EVP_DigestFinal(&mdctx, md, NULL);
+
+	apk_blob_push_blob(&b, APK_BLOB_PTR_LEN(f->diri->dir->name, f->diri->dir->namelen));
+	apk_blob_push_blob(&b, APK_BLOB_STR("/.apk."));
+	apk_blob_push_hexdump(&b, APK_BLOB_PTR_LEN((char *)md, 24));
+	apk_blob_push_blob(&b, APK_BLOB_PTR_LEN("", 1));
+
+	return tmpname;
+}
+
 static int apk_db_install_archive_entry(void *_ctx,
 					const struct apk_file_info *ae,
 					struct apk_istream *is)
@@ -2369,8 +2395,9 @@ static int apk_db_install_archive_entry(void *_ctx,
 	struct apk_installed_package *ipkg = pkg->ipkg;
 	apk_blob_t name = APK_BLOB_STR(ae->name), bdir, bfile;
 	struct apk_db_dir_instance *diri = ctx->diri;
-	struct apk_db_file *file;
+	struct apk_db_file *file, *link_target_file = NULL;
 	int ret = 0, r, type = APK_SCRIPT_INVALID;
+	char tmpname_file[TMPNAME_MAX], tmpname_link_target[TMPNAME_MAX];
 
 	r = apk_sign_ctx_process_file(&ctx->sctx, ae, is);
 	if (r <= 0)
@@ -2437,6 +2464,40 @@ static int apk_db_install_archive_entry(void *_ctx,
 			diri = apk_db_install_directory_entry(ctx, bdir);
 		}
 
+		/* Check hard link target to exist in this package */
+		if (S_ISREG(ae->mode) && ae->link_target) {
+			do {
+				struct apk_db_file *lfile;
+				struct apk_db_dir_instance *ldiri;
+				struct hlist_node *n;
+				apk_blob_t hldir, hlfile;
+
+				if (!apk_blob_rsplit(APK_BLOB_STR(ae->link_target),
+						     '/', &hldir, &hlfile))
+					break;
+
+				ldiri = find_diri(ipkg, hldir, diri, NULL);
+				if (ldiri == NULL)
+					break;
+
+				hlist_for_each_entry(lfile, n, &ldiri->owned_files,
+						     diri_files_list) {
+					if (apk_blob_compare(APK_BLOB_PTR_LEN(lfile->name, lfile->namelen),
+							     hlfile) == 0) {
+						link_target_file = lfile;
+						break;
+					}
+				}
+			} while (0);
+
+			if (!link_target_file) {
+				apk_error(PKG_VER_FMT": "BLOB_FMT": no hard link target (%s) in archive",
+					  PKG_VER_PRINTF(pkg), BLOB_PRINTF(name), ae->link_target);
+				ipkg->broken_files = 1;
+				return 0;
+			}
+		}
+
 		opkg = NULL;
 		file = apk_db_file_query(db, bdir, bfile);
 		if (file != NULL) {
@@ -2495,41 +2556,21 @@ static int apk_db_install_archive_entry(void *_ctx,
 		if (apk_verbosity >= 3)
 			apk_message("%s", ae->name);
 
-		/* Extract the file as name.apk-new */
+		/* Extract the file with temporary name */
 		file->acl = apk_db_acl_atomize(ae->mode, ae->uid, ae->gid, &ae->xattr_csum);
-		r = apk_archive_entry_extract(db->root_fd, ae, ".apk-new", is,
-					      extract_cb, ctx);
+		r = apk_archive_entry_extract(
+				db->root_fd, ae,
+				format_tmpname(pkg, file, tmpname_file),
+				format_tmpname(pkg, link_target_file, tmpname_link_target),
+				is, extract_cb, ctx);
 
 		switch (r) {
 		case 0:
 			/* Hardlinks need special care for checksum */
-			if (ae->csum.type == APK_CHECKSUM_NONE &&
-			    ae->link_target != NULL) {
-				do {
-					struct apk_db_file *lfile;
-					struct apk_db_dir_instance *ldiri;
-					struct hlist_node *n;
-
-					if (!apk_blob_rsplit(APK_BLOB_STR(ae->link_target),
-							     '/', &bdir, &bfile))
-						break;
-
-					ldiri = find_diri(ipkg, bdir, diri, NULL);
-					if (ldiri == NULL)
-						break;
-
-					hlist_for_each_entry(lfile, n, &ldiri->owned_files,
-							     diri_files_list) {
-						if (apk_blob_compare(APK_BLOB_PTR_LEN(lfile->name, lfile->namelen),
-								     bfile) == 0) {
-							memcpy(&file->csum, &lfile->csum,
-							       sizeof(file->csum));
-							break;
-						}
-					}
-				} while (0);
-			} else
-				memcpy(&file->csum, &ae->csum, sizeof(file->csum));
+			if (link_target_file)
+				memcpy(&file->csum, &link_target_file->csum, sizeof file->csum);
+			else
+				memcpy(&file->csum, &ae->csum, sizeof file->csum);
 			break;
 		case -ENOTSUP:
 			ipkg->broken_xattr = 1;
@@ -2547,8 +2588,11 @@ static int apk_db_install_archive_entry(void *_ctx,
 		if (name.ptr[name.len-1] == '/')
 			name.len--;
 
-		diri = apk_db_install_directory_entry(ctx, name);
-		apk_db_dir_prepare(db, diri->dir, ae->mode);
+		diri = ctx->diri = find_diri(ipkg, name, NULL, &ctx->file_diri_node);
+		if (!diri) {
+			diri = apk_db_install_directory_entry(ctx, name);
+			apk_db_dir_prepare(db, diri->dir, ae->mode);
+		}
 		apk_db_diri_set(diri, apk_db_acl_atomize(ae->mode, ae->uid, ae->gid, &ae->xattr_csum));
 	}
 	ctx->installed_size += ctx->current_file_size;
@@ -2558,25 +2602,24 @@ static int apk_db_install_archive_entry(void *_ctx,
 
 static void apk_db_purge_pkg(struct apk_database *db,
 			     struct apk_installed_package *ipkg,
-			     const char *exten)
+			     int is_installed)
 {
 	struct apk_db_dir_instance *diri;
 	struct apk_db_file *file;
 	struct apk_db_file_hash_key key;
 	struct apk_file_info fi;
 	struct hlist_node *dc, *dn, *fc, *fn;
 	unsigned long hash;
-	char name[PATH_MAX];
+	char name[TMPNAME_MAX];
 
 	hlist_for_each_entry_safe(diri, dc, dn, &ipkg->owned_dirs, pkg_dirs_list) {
-		if (exten == NULL)
-			diri->dir->modified = 1;
+		if (is_installed) diri->dir->modified = 1;
 
 		hlist_for_each_entry_safe(file, fc, fn, &diri->owned_files, diri_files_list) {
-			snprintf(name, sizeof(name),
-				 DIR_FILE_FMT "%s",
-				 DIR_FILE_PRINTF(diri->dir, file),
-				 exten ?: "");
+			if (is_installed)
+				snprintf(name, sizeof name, DIR_FILE_FMT, DIR_FILE_PRINTF(diri->dir, file));
+			else
+				format_tmpname(ipkg->pkg, file, name);
 
 			key = (struct apk_db_file_hash_key) {
 				.dirname = APK_BLOB_PTR_LEN(diri->dir->name, diri->dir->namelen),
@@ -2592,7 +2635,7 @@ static void apk_db_purge_pkg(struct apk_database *db,
 			if (apk_verbosity >= 3)
 				apk_message("%s", name);
 			__hlist_del(fc, &diri->owned_files.first);
-			if (exten == NULL) {
+			if (is_installed) {
 				apk_hash_delete_hashed(&db->installed.files, APK_BLOB_BUF(&key), hash);
 				db->installed.stats.files--;
 			}
@@ -2613,18 +2656,16 @@ static void apk_db_migrate_files(struct apk_database *db,
 	struct apk_file_info fi;
 	struct hlist_node *dc, *dn, *fc, *fn;
 	unsigned long hash;
-	char name[PATH_MAX], tmpname[PATH_MAX];
+	char name[PATH_MAX], tmpname[TMPNAME_MAX];
 	int cstype, r;
 
 	hlist_for_each_entry_safe(diri, dc, dn, &ipkg->owned_dirs, pkg_dirs_list) {
 		dir = diri->dir;
 		dir->modified = 1;
 
 		hlist_for_each_entry_safe(file, fc, fn, &diri->owned_files, diri_files_list) {
-			snprintf(name, sizeof(name), DIR_FILE_FMT,
-				 DIR_FILE_PRINTF(diri->dir, file));
-			snprintf(tmpname, sizeof(tmpname), DIR_FILE_FMT ".apk-new",
-				 DIR_FILE_PRINTF(diri->dir, file));
+			snprintf(name, sizeof(name), DIR_FILE_FMT, DIR_FILE_PRINTF(diri->dir, file));
+			format_tmpname(ipkg->pkg, file, tmpname);
 
 			key = (struct apk_db_file_hash_key) {
 				.dirname = APK_BLOB_PTR_LEN(dir->name, dir->namelen),
@@ -2665,8 +2706,21 @@ static void apk_db_migrate_files(struct apk_database *db,
 						APK_FI_NOFOLLOW | file->csum.type, &fi);
 				if ((apk_flags & APK_CLEAN_PROTECTED) ||
 				    (file->csum.type != APK_CHECKSUM_NONE &&
-				     apk_checksum_compare(&file->csum, &fi.csum) == 0))
+				     apk_checksum_compare(&file->csum, &fi.csum) == 0)) {
 					unlinkat(db->root_fd, tmpname, 0);
+				} else {
+					snprintf(name, sizeof name,
+						 DIR_FILE_FMT ".apk-new",
+						 DIR_FILE_PRINTF(diri->dir, file));
+					if (renameat(db->root_fd, tmpname,
+						     db->root_fd, name) != 0) {
+						apk_error(PKG_VER_FMT": failed to rename %s to %s.",
+							  PKG_VER_PRINTF(ipkg->pkg),
+							  tmpname, name);
+						ipkg->broken_files = 1;
+					}
+				}
+
 			} else {
 				/* Overwrite the old file */
 				if (renameat(db->root_fd, tmpname,
@@ -2799,7 +2853,7 @@ int apk_db_install_pkg(struct apk_database *db, struct apk_package *oldpkg,
 		if (ipkg == NULL)
 			goto ret_r;
 		apk_ipkg_run_script(ipkg, db, APK_SCRIPT_PRE_DEINSTALL, script_args);
-		apk_db_purge_pkg(db, ipkg, NULL);
+		apk_db_purge_pkg(db, ipkg, TRUE);
 		apk_ipkg_run_script(ipkg, db, APK_SCRIPT_POST_DEINSTALL, script_args);
 		apk_pkg_uninstall(db, oldpkg);
 		goto ret_r;
@@ -2822,15 +2876,15 @@ int apk_db_install_pkg(struct apk_database *db, struct apk_package *oldpkg,
 				      cb, cb_ctx, script_args);
 		if (r != 0) {
 			if (oldpkg != newpkg)
-				apk_db_purge_pkg(db, ipkg, ".apk-new");
+				apk_db_purge_pkg(db, ipkg, FALSE);
 			apk_pkg_uninstall(db, newpkg);
 			goto ret_r;
 		}
 		apk_db_migrate_files(db, ipkg);
 	}
 
 	if (oldpkg != NULL && oldpkg != newpkg && oldpkg->ipkg != NULL) {
-		apk_db_purge_pkg(db, oldpkg->ipkg, NULL);
+		apk_db_purge_pkg(db, oldpkg->ipkg, TRUE);
 		apk_pkg_uninstall(db, oldpkg);
 	}