lib9p_srv: Proper permission checks, with stubbed group functionalitylukeshu/9p-perms

1 files changed, 129 insertions, 11 deletions

diff --git a/lib9p/srv.c b/lib9p/srv.c
index fb2bd07..2feed56 100644
--- a/lib9p/srv.c
+++ b/lib9p/srv.c
@@ -165,17 +165,6 @@ static inline enum srv_filetype srv_qid_filetype(struct lib9p_qid qid) {
 	return SRV_FILETYPE_FILE;
 }
 
-static inline bool srv_check_perm(struct srv_req *ctx, struct lib9p_srv_stat *stat, uint8_t action) {
-	assert(ctx);
-	assert(stat);
-	assert(action);
-
-	/* TODO actually check user and group instead of just assuming "other".  */
-	uint8_t mode = (uint8_t)(stat->mode & 07);
-
-	return mode & action;
-}
-
 [[gnu::unused]]
 static struct lib9p_srv_userid *srv_userid_new(struct lib9p_s name
 #if CONFIG_9P_ENABLE_9P2000_u || CONFIG_9P_ENABLE_9P2000_L
@@ -230,6 +219,46 @@ static struct lib9p_srv_userid *srv_userid_incref(struct lib9p_srv_userid *useri
 	return userid;
 }
 
+static inline bool srv_user_is_same(struct lib9p_srv_userid *a, struct lib9p_srv_userid *b) {
+	assert(a);
+	assert(b);
+	return lib9p_str_eq(a->name, b->name)
+#if CONFIG_9P_ENABLE_9P2000_u || CONFIG_9P_ENABLE_9P2000_L
+		&& (a->num == b->num)
+#endif
+		;
+}
+
+static inline bool srv_user_is_member(struct lib9p_srv_userid *user, struct lib9p_srv_userid *group) {
+	assert(user);
+	assert(group);
+	/* TODO: Add a way to check group membership.  */
+	return false;
+}
+
+static inline bool srv_user_is_leader(struct lib9p_srv_userid *user, struct lib9p_srv_userid *group) {
+	assert(user);
+	assert(group);
+	/* TODO: Add a way to check group leadership.  */
+	return false;
+}
+
+static inline bool srv_check_perm(struct srv_req *ctx, struct lib9p_srv_stat *stat, uint8_t requested) {
+	assert(ctx);
+	assert(stat);
+	assert(requested);
+
+	uint8_t allowed;
+	if (srv_user_is_same(ctx->user, &stat->owner_uid))
+		allowed = (stat->mode >> 6) & 07;
+	else if (srv_user_is_member(ctx->user, &stat->owner_gid))
+		allowed = (stat->mode >> 3) & 07;
+	else
+		allowed = (stat->mode >> 0) & 07;
+
+	return (requested & ~allowed) == 0;
+}
+
 /**
  * Ensures that `file` is saved into the pathmap, and increments the
  * gc_refcount by 1 (for presumptive insertion into the fidmap).
@@ -1472,10 +1501,99 @@ static void handle_Twstat(struct srv_req *ctx,
                           struct lib9p_msg_Twstat *req) {
 	srv_handler_common(ctx, wstat, req);
 
+	struct srv_fidinfo *fidinfo = map_load(&ctx->parent_sess->fids, req->fid);
+	if (!fidinfo) {
+		lib9p_errorf(&ctx->basectx,
+		             LIB9P_ERRNO_L_EBADF, "bad file number %"PRIu32, req->fid);
+		return;
+	}
+	struct srv_pathinfo *pathinfo = map_load(&ctx->parent_sess->paths, fidinfo->path);
+	assert(pathinfo);
+
+	ctx->user = srv_userid_incref(fidinfo->user);
+	struct lib9p_srv_stat cur_stat = LO_CALL(pathinfo->file, stat, ctx);
+	if (lib9p_ctx_has_error(&ctx->basectx))
+		return;
+	lib9p_srv_stat_assert(cur_stat);
+
+#define is_str_donttouch(VAL) ((VAL).len == 0)
+#define is_int_donttouch(VAL) ((VAL) == ~(typeof(VAL))0)
+
+	if (!is_str_donttouch(req->stat.name) && !lib9p_str_eq(req->stat.name, cur_stat.name)) {
+		if (pathinfo->parent_dir == fidinfo->path) {
+			lib9p_error(&ctx->basectx,
+			            LIB9P_ERRNO_L_EBUSY, "change name: cannot rename root");
+			goto twstat_return;
+		}
+		struct srv_pathinfo *parent = map_load(&ctx->parent_sess->paths, pathinfo->parent_dir);
+		assert(parent);
+		struct lib9p_srv_stat parent_stat = LO_CALL(parent->file, stat, ctx);
+		if (lib9p_ctx_has_error(&ctx->basectx))
+			goto twstat_return;
+		if (!srv_check_perm(ctx, &parent_stat, 0b010)) {
+			lib9p_error(&ctx->basectx,
+			            LIB9P_ERRNO_L_EACCES, "change name: you do not have write permission on the parent directory");
+			goto twstat_return;
+		}
+	}
+	if (!is_int_donttouch(req->stat.length) && req->stat.length != cur_stat.size) {
+		if (!srv_check_perm(ctx, &cur_stat, 0b010)) {
+			lib9p_error(&ctx->basectx,
+			            LIB9P_ERRNO_L_EACCES, "change length: you do not have write permission");
+			goto twstat_return;
+		}
+	}
+	if (!is_int_donttouch(req->stat.mode) && req->stat.mode != cur_stat.mode) {
+		if (!(srv_user_is_same(ctx->user, &cur_stat.owner_uid) || srv_user_is_leader(ctx->user, &cur_stat.owner_gid))) {
+			lib9p_error(&ctx->basectx,
+			            LIB9P_ERRNO_L_EACCES, "change mode: you are neither the owner nor group-leader");
+			goto twstat_return;
+		}
+	}
+	if (!is_int_donttouch(req->stat.mtime) && req->stat.mode != cur_stat.mtime_sec) {
+		if (!(srv_user_is_same(ctx->user, &cur_stat.owner_uid) || srv_user_is_leader(ctx->user, &cur_stat.owner_gid))) {
+			lib9p_error(&ctx->basectx,
+			            LIB9P_ERRNO_L_EACCES, "change mtime: you are neither the owner nor group-leader");
+			goto twstat_return;
+		}
+	}
+	if ((!is_str_donttouch(req->stat.owner_gname) && !lib9p_str_eq(req->stat.owner_gname, cur_stat.owner_gid.name))
+#if CONFIG_9P_ENABLE_9P2000_u
+	    || (ctx->basectx.version == LIB9P_VER_9P2000_u &&
+	        !is_int_donttouch(req->stat.owner_gnum) && req->stat.owner_gnum != cur_stat.owner_gid.num)
+#endif
+	    ) {
+#if CONFIG_9P_ENABLE_9P2000_u
+		if (ctx->basectx.version == LIB9P_VER_9P2000_u) {
+			/* TODO: check that gid==n_gid */
+		}
+#endif
+		struct lib9p_srv_userid new_group = srv_userid_new_stack(req->stat.owner_gname, req->stat.owner_gnum);
+		if (srv_user_is_same(ctx->user, &cur_stat.owner_uid)) {
+			if (!srv_user_is_member(ctx->user, &new_group)) {
+				lib9p_error(&ctx->basectx,
+				            LIB9P_ERRNO_L_EACCES, "change group: you are not a member of the new group");
+				goto twstat_return;
+			}
+		} else if (srv_user_is_leader(ctx->user, &cur_stat.owner_gid)) {
+			if (!srv_user_is_leader(ctx->user, &new_group)) {
+				lib9p_error(&ctx->basectx,
+				            LIB9P_ERRNO_L_EACCES, "change group: you are not a leader of the new group");
+				goto twstat_return;
+			}
+		} else {
+			lib9p_error(&ctx->basectx,
+			            LIB9P_ERRNO_L_EACCES, "change group: you are neither the owner nor group-leader");
+			goto twstat_return;
+		}
+	}
+
 	lib9p_error(&ctx->basectx,
 	            LIB9P_ERRNO_L_EOPNOTSUPP, "wstat not (yet?) implemented");
 
+ twstat_return:
 	srv_respond(ctx, wstat, &resp);
+	ctx->user = srv_userid_decref(ctx->user);
 }
 #endif