From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludo@gnu.org>
Subject: bug#37744: Per-user profile directory hijack (CVE-2019-17365 for Nix)
Date: Wed, 16 Oct 2019 22:01:37 +0200
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In-Reply-To: <87imoook2l.fsf@nckx> (Tobias Geerinckx-Rice's message of "Wed,
 16 Oct 2019 16:12:50 +0200")
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To: Tobias Geerinckx-Rice <me@tobias.gr>
Cc: 37744@debbugs.gnu.org, guix-security@gnu.org

Tobias Geerinckx-Rice <me@tobias.gr> skribis:

> Ludovic Court=C3=A8s =E5=86=99=E9=81=93=EF=BC=9A
>> diff --git a/nix/libstore/local-store.cc
>> b/nix/libstore/local-store.cc
>> index 3b08492c64..3793382361 100644
>> --- a/nix/libstore/local-store.cc
>> +++ b/nix/libstore/local-store.cc
>> @@ -88,8 +88,9 @@ LocalStore::LocalStore(bool reserveSpace)
>>           Path perUserDir =3D profilesDir + "/per-user";
>>          createDirs(perUserDir);
>> -        if (chmod(perUserDir.c_str(), 01777) =3D=3D -1)
>> -            throw SysError(format("could not set permissions on
>> '%1%' to 1777") % perUserDir);
>> +        if (chmod(perUserDir.c_str(), 0755) =3D=3D -1)
>> +            throw SysError(format("could not set permissions on
>> '%1%' to 755")
>> +                           % perUserDir);
>>           mode_t perm =3D 01775;
>
> This is inside
>
>  if (getuid() =3D=3D 0 && settings.buildUsersGroup !=3D "") {
>    =E2=80=A6
>  }
>
> It's not clear to me why the second condition here is relevant, but I
> don't have the big picture.  Nor do I suspect I want it.

Yeah =E2=80=98settings.buildUsersGroup !=3D ""=E2=80=99 probably doesn=E2=
=80=99t make all that
much sense here but it was already there and we strongly discourage
against root without =E2=80=98--build-users-group=E2=80=99 anyway.

Thanks for having lynx eyes!  :-)

Ludo=E2=80=99.