Return-Path: Received: from mail-ig0-f193.google.com ([209.85.213.193]:35008 "EHLO mail-ig0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751470AbcDVUll (ORCPT ); Fri, 22 Apr 2016 16:41:41 -0400 Received: by mail-ig0-f193.google.com with SMTP id fn8so3631923igb.2 for ; Fri, 22 Apr 2016 13:41:41 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <571A6FB0.8080709@RedHat.com> References: <1461186721-64008-1-git-send-email-kolga@netapp.com> <1461186721-64008-3-git-send-email-kolga@netapp.com> <571A6FB0.8080709@RedHat.com> Date: Fri, 22 Apr 2016 16:41:40 -0400 Message-ID: Subject: Re: [RFC PATCH v2 2/3] gssd: using syscalls directly to change thread's identity From: Olga Kornievskaia To: Steve Dickson Cc: Olga Kornievskaia , linux-nfs Content-Type: text/plain; charset=UTF-8 Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, Apr 22, 2016 at 2:38 PM, Steve Dickson wrote: > > > 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; > } > Do you know why we do this before getting the passwd entry? Doing as you suggest causes problems as in it it fails to drop the supplementary groups. > steved. > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html