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Improve the cowboy_static consistency across platforms

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As a result we explictly reject path_info components that include
a forward slash, backward slash or NUL character. This only applies
to the [...] part of the path for dir/priv_dir configuration.

Also improve the tests so that they work on Windows.
This commit is contained in:
Loïc Hoguin 2019-09-07 12:18:16 +02:00
parent 36836594f8
commit 4427108b69
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2 changed files with 65 additions and 38 deletions
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70
src/cowboy_static.erl
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@ -119,35 +119,51 @@ init_dir(Req, Path, HowToAccess, Extra) when is_list(Path) ->
init_dir(Req, list_to_binary(Path), HowToAccess, Extra);
init_dir(Req, Path, HowToAccess, Extra) ->
Dir = fullpath(filename:absname(Path)),
PathInfo = cowboy_req:path_info(Req),
Filepath = filename:join([Dir|escape_reserved(PathInfo)]),
Len = byte_size(Dir),
case fullpath(Filepath) of
<< Dir:Len/binary, $/, _/binary >> ->
init_info(Req, Filepath, HowToAccess, Extra);
<< Dir:Len/binary >> ->
init_info(Req, Filepath, HowToAccess, Extra);
_ ->
{cowboy_rest, Req, error}
case cowboy_req:path_info(Req) of
%% When dir/priv_dir are used and there is no path_info
%% this is a configuration error and we abort immediately.
undefined ->
{ok, cowboy_req:reply(500, Req), error};
PathInfo ->
case validate_reserved(PathInfo) of
error ->
{cowboy_rest, Req, error};
ok ->
Filepath = filename:join([Dir|PathInfo]),
Len = byte_size(Dir),
case fullpath(Filepath) of
<< Dir:Len/binary, $/, _/binary >> ->
init_info(Req, Filepath, HowToAccess, Extra);
<< Dir:Len/binary >> ->
init_info(Req, Filepath, HowToAccess, Extra);
_ ->
{cowboy_rest, Req, error}
end
end
end.
escape_reserved([]) -> [];
escape_reserved([P|Tail]) -> [escape_reserved(P, <<>>)|escape_reserved(Tail)].
validate_reserved([]) ->
ok;
validate_reserved([P|Tail]) ->
case validate_reserved1(P) of
ok -> validate_reserved(Tail);
error -> error
end.
%% We escape the slash found in path segments because
%% a segment corresponds to a directory entry, and
%% therefore those slashes are expected to be part of
%% the directory name.
%%
%% Note that on most systems the slash is prohibited
%% and cannot appear in filenames, which means the
%% requested file will end up being not found.
escape_reserved(<<>>, Acc) ->
Acc;
escape_reserved(<< $/, Rest/bits >>, Acc) ->
escape_reserved(Rest, << Acc/binary, $\\, $/ >>);
escape_reserved(<< C, Rest/bits >>, Acc) ->
escape_reserved(Rest, << Acc/binary, C >>).
%% We always reject forward slash, backward slash and NUL as
%% those have special meanings across the supported platforms.
%% We could support the backward slash on some platforms but
%% for the sake of consistency and simplicity we don't.
validate_reserved1(<<>>) ->
ok;
validate_reserved1(<<$/, _/bits>>) ->
error;
validate_reserved1(<<$\\, _/bits>>) ->
error;
validate_reserved1(<<0, _/bits>>) ->
error;
validate_reserved1(<<_, Rest/bits>>) ->
validate_reserved1(Rest).
fullpath(Path) ->
fullpath(filename:split(Path), []).
@ -290,7 +306,7 @@ bad_path_win32_check_test_() ->
-endif.
%% Reject requests that tried to access a file outside
%% the target directory.
%% the target directory, or used reserved characters.
-spec malformed_request(Req, State)
-> {boolean(), Req, State}.