fence fileshares to just those files

when a share is created for just a single file, it was possible to
guess other filenames in the source folder and access those files

copyparty/authsrv.py

@@ -431,6 +431,8 @@ class VFS(object):
 
         self.get_dbv = self._get_dbv
         self.ls = self._ls
+        self.canonical = self._canonical
+        self.dcanonical = self._dcanonical
 
     def __repr__(self) -> str:
         return "VFS(%s)" % (
@@ -624,7 +626,7 @@ class VFS(object):
         vrem = vjoin(self.vpath[len(dbv.vpath) :].lstrip("/"), vrem)
         return dbv, vrem
 
-    def canonical(self, rem: str, resolve: bool = True) -> str:
+    def _canonical(self, rem: str, resolve: bool = True) -> str:
         """returns the canonical path (fully-resolved absolute fs path)"""
         ap = self.realpath
         if rem:
@@ -632,7 +634,7 @@ class VFS(object):
 
         return absreal(ap) if resolve else ap
 
-    def dcanonical(self, rem: str) -> str:
+    def _dcanonical(self, rem: str) -> str:
         """resolves until the final component (filename)"""
         ap = self.realpath
         if rem:
@@ -641,6 +643,44 @@ class VFS(object):
         ad, fn = os.path.split(ap)
         return os.path.join(absreal(ad), fn)
 
+    def _canonical_shr(self, rem: str, resolve: bool = True) -> str:
+        """returns the canonical path (fully-resolved absolute fs path)"""
+        ap = self.realpath
+        if rem:
+            ap += "/" + rem
+
+        rap = absreal(ap)
+        if self.shr_files:
+            assert self.shr_src  # !rm
+            vn, rem = self.shr_src
+            chk = absreal(os.path.join(vn.realpath, rem))
+            if chk != rap:
+                # not the dir itself; assert file allowed
+                ad, fn = os.path.split(rap)
+                if chk != ad or fn not in self.shr_files:
+                    return "\n\n"
+
+        return rap if resolve else ap
+
+    def _dcanonical_shr(self, rem: str) -> str:
+        """resolves until the final component (filename)"""
+        ap = self.realpath
+        if rem:
+            ap += "/" + rem
+
+        ad, fn = os.path.split(ap)
+        ad = absreal(ad)
+        if self.shr_files:
+            assert self.shr_src  # !rm
+            vn, rem = self.shr_src
+            chk = absreal(os.path.join(vn.realpath, rem))
+            if chk != absreal(ap):
+                # not the dir itself; assert file allowed
+                if ad != chk or fn not in self.shr_files:
+                    return "\n\n"
+
+        return os.path.join(ad, fn)
+
     def _ls_nope(
         self, *a, **ka
     ) -> tuple[str, list[tuple[str, os.stat_result]], dict[str, "VFS"]]:
@@ -2751,6 +2791,8 @@ class AuthSrv(object):
 
                     shn.shr_files = set(fns)
                     shn.ls = shn._ls_shr
+                    shn.canonical = shn._canonical_shr
+                    shn.dcanonical = shn._dcanonical_shr
                 else:
                     shn.ls = shn._ls