File 0776-Fix-filelib-safe_relative_path-2.patch of Package erlang

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File 0776-Fix-filelib-safe_relative_path-2.patch of Package erlang (Revision e1db283a562e295f06bdb5f0f8cb2214)

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From 8e83401d041313907f7c1b94fa6ef294f610d1ef Mon Sep 17 00:00:00 2001
From: Jan Uhlig <juhlig@hnc-agency.org>
Date: Thu, 4 May 2023 15:38:29 +0200
Subject: [PATCH] Fix filelib:safe_relative_path/2
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The function would return a wrong path if the second argument was a link
and the path in the first argument would descend and then ascend again to
the top level.

The function would also report a path as unsafe by falsely detecting a
link loop if a link would target another link, which in turn would target
a file of the same name like bar --> foo/bar --> (foo/)foo/bar.

Co-authored-by: Björn Gustavsson <bgustavsson@gmail.com>
---
 lib/stdlib/src/filelib.erl        | 110 +++++++++++++++---------------
 lib/stdlib/test/filelib_SUITE.erl |  31 ++++++++-
 2 files changed, 85 insertions(+), 56 deletions(-)

diff --git a/lib/stdlib/src/filelib.erl b/lib/stdlib/src/filelib.erl
index de08352398..2f0ff53744 100644
--- a/lib/stdlib/src/filelib.erl
+++ b/lib/stdlib/src/filelib.erl
@@ -770,65 +770,65 @@ find_regular_file([File|Files]) ->
       Cwd :: filename_all(),
       SafeFilename :: filename_all().
 
+safe_relative_path(Path, "") ->
+    safe_relative_path(Path, ".");
 safe_relative_path(Path, Cwd) ->
-    case filename:pathtype(Path) of
-        relative -> safe_relative_path(filename:split(Path), Cwd, [], "");
-        _ -> unsafe
-    end.
-
-safe_relative_path([], _Cwd, _PrevLinks, Acc) ->
-    Acc;
-
-safe_relative_path([Segment | Segments], Cwd, PrevLinks, Acc) ->
-    AccSegment = join(Acc, Segment),
-    case safe_relative_path(AccSegment) of
-        unsafe ->
-            unsafe;
-        SafeAccSegment ->
-            case file:read_link(join(Cwd, SafeAccSegment)) of
-                {ok, LinkPath} ->
-                    case lists:member(LinkPath, PrevLinks) of
-                        true ->
-                            unsafe;
-                        false ->
-                            case safe_relative_path(filename:split(LinkPath), Cwd, [LinkPath | PrevLinks], Acc) of
-                                unsafe -> unsafe;
-                                NewAcc -> safe_relative_path(Segments, Cwd, [], NewAcc)
-                            end
-                    end;
-                {error, _} ->
-                    safe_relative_path(Segments, Cwd, PrevLinks, SafeAccSegment)
-            end
-  end.
-
-join([], Path) -> Path;
-join(Left, Right) -> filename:join(Left, Right).
-
-safe_relative_path(Path) ->
-    case filename:pathtype(Path) of
+    srp_path(filename:split(Path),
+             Cwd,
+             sets:new([{version, 2}]),
+             []).
+
+srp_path([], _Cwd, _Seen, []) ->
+    "";
+srp_path([], _Cwd, _Seen, Acc) ->
+    filename:join(Acc);
+srp_path(["."|Segs], Cwd, Seen, Acc) ->
+    srp_path(Segs, Cwd, Seen, Acc);
+srp_path([<<".">>|Segs], Cwd, Seen, Acc) ->
+    srp_path(Segs, Cwd, Seen, Acc);
+srp_path([".."|_Segs], _Cwd, _Seen, []) ->
+    unsafe;
+srp_path([".."|Segs], Cwd, Seen, [_|_]=Acc) ->
+    srp_path(Segs, Cwd, Seen, lists:droplast(Acc));
+srp_path([<<"..">>|_Segs], _Cwd, _Seen, []) ->
+    unsafe;
+srp_path([<<"..">>|Segs], Cwd, Seen, [_|_]=Acc) ->
+    srp_path(Segs, Cwd, Seen, lists:droplast(Acc));
+srp_path([clear|Segs], Cwd, _Seen, Acc) ->
+    srp_path(Segs, Cwd, sets:new([{version, 2}]), Acc);
+srp_path([Seg|_]=Segs, Cwd, Seen, Acc) ->
+    case filename:pathtype(Seg) of
         relative ->
-            Cs0 = filename:split(Path),
-            safe_relative_path_1(Cs0, []);
+            srp_segment(Segs, Cwd, Seen, Acc);
         _ ->
             unsafe
     end.
 
-safe_relative_path_1(["."|T], Acc) ->
-    safe_relative_path_1(T, Acc);
-safe_relative_path_1([<<".">>|T], Acc) ->
-    safe_relative_path_1(T, Acc);
-safe_relative_path_1([".."|T], Acc) ->
-    climb(T, Acc);
-safe_relative_path_1([<<"..">>|T], Acc) ->
-    climb(T, Acc);
-safe_relative_path_1([H|T], Acc) ->
-    safe_relative_path_1(T, [H|Acc]);
-safe_relative_path_1([], []) ->
-    [];
-safe_relative_path_1([], Acc) ->
-    filename:join(lists:reverse(Acc)).
+srp_segment([Seg|Segs], Cwd, Seen, Acc) ->
+    Path = filename:join([Cwd|Acc]),
+    case file:read_link(filename:join(Path, Seg)) of
+        {ok, LinkPath} ->
+            srp_link(Path,
+                     LinkPath,
+                     Segs,
+                     Cwd,
+                     Seen,
+                     Acc);
+        {error, _} ->
+            srp_path(Segs,
+                     Cwd,
+                     Seen,
+                     Acc++[Seg])
+    end.
 
-climb(_, []) ->
-    unsafe;
-climb(T, [_|Acc]) ->
-    safe_relative_path_1(T, Acc).
+srp_link(Path, LinkPath, Segs, Cwd, Seen, Acc) ->
+    FullLinkPath = filename:join(Path, LinkPath),
+    case sets:is_element(FullLinkPath, Seen) of
+        true ->
+            unsafe;
+        false ->
+            srp_path(filename:split(LinkPath)++[clear|Segs],
+                     Cwd,
+                     sets:add_element(FullLinkPath, Seen),
+                     Acc)
+    end.
diff --git a/lib/stdlib/test/filelib_SUITE.erl b/lib/stdlib/test/filelib_SUITE.erl
index 179567f128..8b5e9c6377 100644
--- a/lib/stdlib/test/filelib_SUITE.erl
+++ b/lib/stdlib/test/filelib_SUITE.erl
@@ -840,7 +840,10 @@ safe_relative_path_links(Config) ->
                 nested_links_test(BaseDir),
                 loop_test(BaseDir),
                 loop_with_parent_test(BaseDir),
-                revist_links_test(BaseDir);
+                revist_links_test(BaseDir),
+                descend_climb_cwd_link_test(BaseDir),
+                chained_links_same_target_name_test(BaseDir),
+                ok;
             false ->
                 {skipped, "This platform/user can't create symlinks."}
         end
@@ -914,6 +917,32 @@ revist_links_test(BaseDir) ->
     "file" = filelib:safe_relative_path("x/x/y/y/file", filename:join(BaseDir, "revist_links_test")),
     "file" = filelib:safe_relative_path("x/z/y/x/./z/foo/../x/./y/file", filename:join(BaseDir, "revist_links_test")).
 
+descend_climb_cwd_link_test(BaseDir) ->
+    Dir = filename:join(BaseDir, ?FUNCTION_NAME),
+
+    ok = file:make_dir(Dir),
+    ok = file:make_dir(filename:join(Dir, "cwd")),
+
+    ok = file:make_symlink("cwd", filename:join(Dir, "cwd_link")),
+
+    "" = filelib:safe_relative_path("foo/..", filename:join(Dir, "cwd_link")),
+    "bar" = filelib:safe_relative_path("foo/../bar", filename:join(Dir, "cwd_link")),
+    "" = filelib:safe_relative_path("foo/..", filename:join(Dir, "cwd")),
+    "bar" = filelib:safe_relative_path("foo/../bar", filename:join(Dir, "cwd")).
+
+chained_links_same_target_name_test(BaseDir) ->
+    Dir = filename:join(BaseDir, ?FUNCTION_NAME),
+
+    ok = file:make_dir(Dir),
+    ok = file:make_dir(filename:join(Dir, "foo")),
+    ok = file:make_dir(filename:join(Dir, "foo/foo")),
+    ok = file:make_dir(filename:join(Dir, "foo/foo/bar")),
+
+    ok = file:make_symlink("foo/bar", filename:join(Dir, "foo/bar")),
+    ok = file:make_symlink("foo/bar", filename:join(Dir, "bar")),
+
+    "foo/foo/bar" = filelib:safe_relative_path("bar", Dir).
+
 rm_rf(Dir) ->
     case file:read_link_info(Dir) of
         {ok, #file_info{type = directory}} ->
-- 
2.35.3

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File 0776-Fix-filelib-safe_relative_path-2.patch of Package erlang (Revision e1db283a562e295f06bdb5f0f8cb2214)

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