From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:54720 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751718AbcDVSil (ORCPT ); Fri, 22 Apr 2016 14:38:41 -0400 Subject: Re: [RFC PATCH v2 2/3] gssd: using syscalls directly to change thread's identity To: Olga Kornievskaia References: <1461186721-64008-1-git-send-email-kolga@netapp.com> <1461186721-64008-3-git-send-email-kolga@netapp.com> Cc: linux-nfs@vger.kernel.org From: Steve Dickson Message-ID: <571A6FB0.8080709@RedHat.com> Date: Fri, 22 Apr 2016 14:38:40 -0400 MIME-Version: 1.0 In-Reply-To: <1461186721-64008-3-git-send-email-kolga@netapp.com> Content-Type: text/plain; charset=windows-1252 Sender: linux-nfs-owner@vger.kernel.org List-ID: On 04/20/2016 05:12 PM, 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 | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/utils/gssd/gssd_proc.c b/utils/gssd/gssd_proc.c > index 581a125..5d9a6db 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" > @@ -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) { > printerr(0, "WARNING: Failed to setuid for user with uid %u\n", > uid); > return errno; > We also have to do the same thing to the setgroups() call at the top of change_identity(). So add the following diff to this patch and we are good to go... diff --git a/utils/gssd/gssd_proc.c b/utils/gssd/gssd_proc.c index e651d71..2f9f8ab 100644 --- a/utils/gssd/gssd_proc.c +++ b/utils/gssd/gssd_proc.c @@ -437,7 +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; } steved.