File 2363-erl_tar-Handle-leading-slashes-and-directo... of Package erlang

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File 2363-erl_tar-Handle-leading-slashes-and-directory-travers.patch of Package erlang (Revision ef2f13a3fd79ccee295941d812fb0579)

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From 05f20a9790fa88011c1ce7099e0a660aa83195a9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Fri, 7 Apr 2017 13:07:48 +0200
Subject: [PATCH 2/2] erl_tar: Handle leading slashes and directory traversal
 attacks

---
 lib/stdlib/doc/src/erl_tar.xml |  4 +++
 lib/stdlib/src/erl_tar.erl     | 59 ++++++++++++++++++++++++++++--------------
 lib/stdlib/test/tar_SUITE.erl  | 37 ++++++++++++++++++++++++--
 3 files changed, 79 insertions(+), 21 deletions(-)

diff --git a/lib/stdlib/doc/src/erl_tar.xml b/lib/stdlib/doc/src/erl_tar.xml
index f28d8b425..fab7c832d 100644
--- a/lib/stdlib/doc/src/erl_tar.xml
+++ b/lib/stdlib/doc/src/erl_tar.xml
@@ -292,6 +292,10 @@
 <c>Fd</c> is assumed to be a file descriptor returned from function
 <c>file:open/2</c>.
 Otherwise, <c>Name</c> is to be a filename.
+	<note>Leading slashes in tar member names will be removed before
+	writing the file. That is, absolute paths will be turned into
+	relative paths. There will be an info message written to the error
+	logger when paths are changed in this way.</note>
 </desc>
 </func>
 
diff --git a/lib/stdlib/src/erl_tar.erl b/lib/stdlib/src/erl_tar.erl
index a54df939b..168ea4002 100644
--- a/lib/stdlib/src/erl_tar.erl
+++ b/lib/stdlib/src/erl_tar.erl
@@ -69,6 +69,8 @@ format_error(invalid_gnu_1_0_sparsemap) ->
 "Invalid GNU sparse map (version 1.0)";
 format_error({invalid_gnu_0_1_sparsemap, Format}) ->
 lists:flatten(io_lib:format("Invalid GNU sparse map (version ~s)", [Format]));
+format_error(unsafe_path) ->
+ "The path points above the current working directory";
 format_error({Name,Reason}) ->
 lists:flatten(io_lib:format("~ts: ~ts", [Name,format_error(Reason)]));
 format_error(Atom) when is_atom(Atom) ->
@@ -120,26 +122,38 @@ do_extract(Handle, Opts) when is_list(Opts) ->
 
 extract1(eof, Reader, _, Acc) when is_list(Acc) ->
 {ok, {ok, lists:reverse(Acc)}, Reader};
+extract1(eof, Reader, _, leading_slash) ->
+ error_logger:info_msg("erl_tar: removed leading '/' from member names\n"),
+ {ok, ok, Reader};
 extract1(eof, Reader, _, Acc) ->
 {ok, Acc, Reader};
-extract1(#tar_header{name=Name,size=Size}=Header, Reader, Opts, Acc) ->
+extract1(#tar_header{name=Name,size=Size}=Header, Reader0, Opts, Acc0) ->
 case check_extract(Name, Opts) of
 true ->
- case do_read(Reader, Size) of
- {ok, Bin, Reader2} ->
- case write_extracted_element(Header, Bin, Opts) of
- ok ->
- {ok, Acc, Reader2};
- {ok, NameBin} when is_list(Acc) ->
- {ok, [NameBin | Acc], Reader2};
- {error, _} = Err ->
- throw(Err)
- end;
+ case do_read(Reader0, Size) of
+ {ok, Bin, Reader1} ->
+ Acc = extract2(Header, Bin, Opts, Acc0),
+ {ok, Acc, Reader1};
 {error, _} = Err ->
 throw(Err)
 end;
 false ->
- {ok, Acc, skip_file(Reader)}
+ {ok, Acc0, skip_file(Reader0)}
+ end.
+
+extract2(Header, Bin, Opts, Acc) ->
+ case write_extracted_element(Header, Bin, Opts) of
+ ok ->
+ case Header of
+ #tar_header{name="/"++_} ->
+ leading_slash;
+ #tar_header{} ->
+ Acc
+ end;
+ {ok, NameBin} when is_list(Acc) ->
+ [NameBin | Acc];
+ {error, _} = Err ->
+ throw(Err)
 end.
 
 %% Checks if the file Name should be extracted.
@@ -1052,14 +1066,11 @@ unpack_modern(Format, #header_v7{}=V7, Bin, #tar_header{}=Header0)
 
 
 safe_join_path([], Name) ->
- strip_slashes(Name, both);
+ filename:join([Name]);
 safe_join_path(Prefix, []) ->
- strip_slashes(Prefix, right);
+ filename:join([Prefix]);
 safe_join_path(Prefix, Name) ->
- filename:join(strip_slashes(Prefix, right), strip_slashes(Name, both)).
-
-strip_slashes(Str, Direction) ->
- string:strip(Str, Direction, $/).
+ filename:join(Prefix, Name).
 
 new_sparse_file_reader(Reader, Sparsemap, RealSize) ->
 true = validate_sparse_entries(Sparsemap, RealSize),
@@ -1557,7 +1568,7 @@ write_extracted_element(#tar_header{name=Name,typeflag=Type},
 ok
 end;
 write_extracted_element(#tar_header{name=Name0}=Header, Bin, Opts) ->
- Name1 = filename:absname(Name0, Opts#read_opts.cwd),
+ Name1 = make_safe_path(Name0, Opts),
 Created =
 case typeflag(Header#tar_header.typeflag) of
 regular ->
@@ -1585,6 +1596,16 @@ write_extracted_element(#tar_header{name=Name0}=Header, Bin, Opts) ->
 not_written -> ok
 end.
 
+make_safe_path([$/|Path], Opts) ->
+ make_safe_path(Path, Opts);
+make_safe_path(Path, #read_opts{cwd=Cwd}) ->
+ case filename:safe_relative_path(Path) of
+ unsafe ->
+ throw({error,{Path,unsafe_path}});
+ SafePath ->
+ filename:absname(SafePath, Cwd)
+ end.
+
 create_regular(Name, NameInArchive, Bin, Opts) ->
 case write_extracted_file(Name, Bin, Opts) of
 not_written ->
diff --git a/lib/stdlib/test/tar_SUITE.erl b/lib/stdlib/test/tar_SUITE.erl
index 2e1ae7bcf..76fa760fa 100644
--- a/lib/stdlib/test/tar_SUITE.erl
+++ b/lib/stdlib/test/tar_SUITE.erl
@@ -27,7 +27,7 @@
 	 extract_from_binary_compressed/1, extract_filtered/1,
 	 extract_from_open_file/1, symlinks/1, open_add_close/1, cooked_compressed/1,
 	 memory/1,unicode/1,read_other_implementations/1,
- sparse/1, init/1]).
+ sparse/1, init/1, leading_slash/1, dotdot/1]).
 
 -include_lib("common_test/include/ct.hrl").
 -include_lib("kernel/include/file.hrl").
@@ -41,7 +41,7 @@ all() ->
 extract_filtered,
 symlinks, open_add_close, cooked_compressed, memory, unicode,
 read_other_implementations,
- sparse,init].
+ sparse,init,leading_slash,dotdot].
 
 groups() -> 
 [].
@@ -920,6 +920,39 @@ unicode_create_files() ->
 		 []
 	 end].
 
+leading_slash(Config) ->
+ PrivDir = proplists:get_value(priv_dir, Config),
+ Dir = filename:join(PrivDir, ?FUNCTION_NAME),
+ TarFile = filename:join(Dir, "leading_slash.tar"),
+ ok = filelib:ensure_dir(TarFile),
+ {ok,Fd} = erl_tar:open(TarFile, [write]),
+ TarMemberName = "e/d/c/b/a_member",
+ TarMemberNameAbs = "/" ++ TarMemberName,
+ Contents = <<"contents\n">>,
+ ok = erl_tar:add(Fd, Contents, TarMemberNameAbs, [verbose]),
+ ok = erl_tar:close(Fd),
+
+ ok = erl_tar:extract(TarFile, [{cwd,Dir}]),
+
+ {ok,Contents} = file:read_file(filename:join(Dir, TarMemberName)),
+ ok.
+
+dotdot(Config) ->
+ PrivDir = proplists:get_value(priv_dir, Config),
+ Dir = filename:join(PrivDir, ?FUNCTION_NAME),
+ ok = file:make_dir(Dir),
+ Tar = filename:join(Dir, "dotdot.tar"),
+ {ok,Fd} = erl_tar:open(Tar, [write]),
+ BeamFile = code:which(?MODULE),
+ ok = erl_tar:add(Fd, BeamFile, "a/./../../some_file", []),
+ ok = erl_tar:close(Fd),
+
+ {error,{_,unsafe_path=Error}} = erl_tar:extract(Tar, [{cwd,Dir}]),
+ false = filelib:is_regular(filename:join(PrivDir, "some_file")),
+ io:format("~s\n", [erl_tar:format_error(Error)]),
+
+ ok.
+
 %% Delete the given list of files.
 delete_files([]) -> ok;
 delete_files([Item|Rest]) ->
-- 
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