From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f179.google.com ([209.85.220.179]:33907 "EHLO mail-qk0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964800AbcDYUXQ (ORCPT ); Mon, 25 Apr 2016 16:23:16 -0400 Received: by mail-qk0-f179.google.com with SMTP id r184so67188420qkc.1 for ; Mon, 25 Apr 2016 13:23:16 -0700 (PDT) Message-ID: <1461615792.4288.31.camel@poochiereds.net> Subject: Re: [PATCH v3 2/3] gssd: using syscalls directly to change thread's identity From: Jeff Layton To: Olga Kornievskaia , steved@redhat.com Cc: linux-nfs@vger.kernel.org Date: Mon, 25 Apr 2016 16:23:12 -0400 In-Reply-To: <1461603513-67523-3-git-send-email-kolga@netapp.com> References: <1461603513-67523-1-git-send-email-kolga@netapp.com> <1461603513-67523-3-git-send-email-kolga@netapp.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org List-ID: On Mon, 2016-04-25 at 12:58 -0400, Olga Kornievskaia wrote: > For the threaded version we have to set uid,gid per thread instead > of per process. glibc setresuid() when called from a thread, it'll > send a signal to all other threads to synchronize the uid in all > other threads. To bypass this, we have to call syscall() directly. > > Signed-off-by: Olga Kornievskaia > Reviewed-by: Steve Dickson > --- >  utils/gssd/gssd_proc.c | 12 +++++++++--- >  1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/utils/gssd/gssd_proc.c b/utils/gssd/gssd_proc.c > index e2e95dc..487a4f5 100644 > --- a/utils/gssd/gssd_proc.c > +++ b/utils/gssd/gssd_proc.c > @@ -69,6 +69,7 @@ >  #include >  #include >  #include > +#include >   >  #include "gssd.h" >  #include "err_util.h" > @@ -436,7 +437,7 @@ change_identity(uid_t uid) >   struct passwd *pw; >   >   /* drop list of supplimentary groups first */ > - if (setgroups(0, NULL) != 0) { > + if (syscall(SYS_setgroups, 0) != 0) { >   printerr(0, "WARNING: unable to drop supplimentary groups!"); >   return errno; >   } > @@ -457,7 +458,12 @@ change_identity(uid_t uid) >    * Switch the GIDs. Note that we leave the saved-set-gid alone in an >    * attempt to prevent attacks via ptrace() >    */ > - if (setresgid(pw->pw_gid, pw->pw_gid, -1) != 0) { > + /* For the threaded version we have to set uid,gid per thread instead > +  * of per process. glibc setresuid() when called from a thread, it'll > +  * send a signal to all other threads to synchronize the uid in all > +  * other threads. To bypass this, we have to call syscall() directly. > +  */ > + if (syscall(SYS_setresgid, pw->pw_gid) != 0) { >   printerr(0, "WARNING: failed to set gid to %u!\n", pw->pw_gid); >   return errno; >   } > @@ -466,7 +472,7 @@ change_identity(uid_t uid) >    * Switch UIDs, but leave saved-set-uid alone to prevent ptrace() by >    * other processes running with this uid. >    */ > - if (setresuid(uid, uid, -1) != 0) { > + if (syscall(SYS_setresuid, uid) != 0) { That looks wrong. setresuid takes 3 arguments: SYSCALL_DEFINE3(setresuid, uid_t, ruid, uid_t, euid, uid_t, suid) Ditto for setresgid above. syscall is a varargs function, so you really _must_ pass in the right number of args or you'll end up feeding it random junk in registers or off the stack. The compiler won't save you here... >  printerr(0, "WARNING: Failed to setuid for user with uid %u\n", >   uid); >   return errno; -- Jeff Layton