From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gabriel-Andrew Pollo-Guilbert Subject: [lttng-ust RFC v2] Add setuid wrapper for per-UID buffers Date: Wed, 22 May 2019 11:48:55 -0400 Message-ID: <20190522154855.20846-1-gabriel.pollo-guilbert__44085.2759218373$1558540201$gmane$org@efficios.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail.efficios.com (mail.efficios.com [167.114.142.138]) by lists.lttng.org (Postfix) with ESMTPS id 458HBW1M6rzyXh for ; Wed, 22 May 2019 11:49:38 -0400 (EDT) List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" To: lttng-dev@lists.lttng.org List-Id: lttng-dev@lists.lttng.org In case of a per-UID buffer, events following a setuid() call should be forwarded to buffers of the new UID. In order to do so, we add a wrapper around setuid() that unregister and re-register the application from the session daemon. Signed-off-by: Gabriel-Andrew Pollo-Guilbert --- Makefile.am | 1 + configure.ac | 1 + doc/man/lttng-ust.3.txt | 11 ++++++++ include/lttng/ust.h | 1 + liblttng-ust-setuid/Makefile.am | 10 +++++++ liblttng-ust-setuid/ustsetuid.c | 47 +++++++++++++++++++++++++++++++++ liblttng-ust/lttng-ust-comm.c | 29 ++++++++++++++++++-- 7 files changed, 98 insertions(+), 2 deletions(-) create mode 100644 liblttng-ust-setuid/Makefile.am create mode 100644 liblttng-ust-setuid/ustsetuid.c diff --git a/Makefile.am b/Makefile.am index 810761ca..e8812e59 100644 --- a/Makefile.am +++ b/Makefile.am @@ -5,6 +5,7 @@ SUBDIRS = . include snprintf libringbuffer liblttng-ust-comm \ liblttng-ust-ctl \ liblttng-ust-fd \ liblttng-ust-fork \ + liblttng-ust-setuid \ liblttng-ust-libc-wrapper \ liblttng-ust-cyg-profile \ tools diff --git a/configure.ac b/configure.ac index 52fc3f68..95780dba 100644 --- a/configure.ac +++ b/configure.ac @@ -522,6 +522,7 @@ AC_CONFIG_FILES([ liblttng-ust/Makefile liblttng-ust-ctl/Makefile liblttng-ust-fork/Makefile + liblttng-ust-setuid/Makefile liblttng-ust-dl/Makefile liblttng-ust-fd/Makefile liblttng-ust-java/Makefile diff --git a/doc/man/lttng-ust.3.txt b/doc/man/lttng-ust.3.txt index 5c9c9f5d..b252c11d 100644 --- a/doc/man/lttng-ust.3.txt +++ b/doc/man/lttng-ust.3.txt @@ -744,6 +744,17 @@ library before you start the application. Typical use cases include daemons closing all file descriptors after man:fork(2), and buggy applications doing ``double-closes''. +Using LTTng-UST with applications that change user +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If your application is traced using per-UID buffers and changes user ID using +man:setuid(2), the library `liblttng-ust-setuid.so` needs to be preloaded +before starting the application with the `LD_PRELOAD` environment variable (see +man:ld.so(8)). This way, events generated after the UID change will be fowarded +to the correct buffer. + +This workaround requires that the tracing session be global (root +lttng-sessiond) in order to avoid permission problems between a session +daemon started by another user. Context information ~~~~~~~~~~~~~~~~~~~ diff --git a/include/lttng/ust.h b/include/lttng/ust.h index 2779d7a7..5495e564 100644 --- a/include/lttng/ust.h +++ b/include/lttng/ust.h @@ -32,6 +32,7 @@ extern "C" { extern void ust_before_fork(sigset_t *save_sigset); extern void ust_after_fork_parent(sigset_t *restore_sigset); extern void ust_after_fork_child(sigset_t *restore_sigset); +extern void ust_after_setuid(void); #ifdef __cplusplus } diff --git a/liblttng-ust-setuid/Makefile.am b/liblttng-ust-setuid/Makefile.am new file mode 100644 index 00000000..df3cd622 --- /dev/null +++ b/liblttng-ust-setuid/Makefile.am @@ -0,0 +1,10 @@ +AM_CPPFLAGS = -I$(top_srcdir)/include +AM_CFLAGS += -fno-strict-aliasing + +lib_LTLIBRARIES = liblttng-ust-setuid.la +liblttng_ust_setuid_la_SOURCES = ustsetuid.c +liblttng_ust_setuid_la_LIBADD = \ + $(top_builddir)/liblttng-ust/liblttng-ust.la \ + $(DL_LIBS) + +liblttng_ust_setuid_la_CFLAGS = -DUST_COMPONENT=liblttng-ust-setuid $(AM_CFLAGS) diff --git a/liblttng-ust-setuid/ustsetuid.c b/liblttng-ust-setuid/ustsetuid.c new file mode 100644 index 00000000..8cae9a43 --- /dev/null +++ b/liblttng-ust-setuid/ustsetuid.c @@ -0,0 +1,47 @@ +/* + * Copyright (C) 2019 Gabriel-Andrew Pollo-Guilbert + * + * This library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; version 2.1 of + * the License. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this library; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + */ + +#define _GNU_SOURCE +#include +#include +#include +#include +#include + +int setuid(uid_t uid) +{ + static int (*plibc_func)(uid_t) = NULL; + int retval; + + if (plibc_func == NULL) { + plibc_func = dlsym(RTLD_NEXT, "setuid"); + if (plibc_func == NULL) { + fprintf(stderr, "libustsetuid: unable to find \"setuid\" symbol\n"); + errno = ENOSYS; + return -1; + } + } + + retval = plibc_func(uid); + if (retval < 0) + return retval; + + ust_after_setuid(); + + return retval; +} diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c index 61dbb41b..0d0b9eb4 100644 --- a/liblttng-ust/lttng-ust-comm.c +++ b/liblttng-ust/lttng-ust-comm.c @@ -225,10 +225,12 @@ void ust_unlock(void) * daemon problems). */ static sem_t constructor_wait; + /* * Doing this for both the global and local sessiond. */ -static int sem_count = { 2 }; +#define LTTNG_UST_INIT_SEM_COUNT 2 +static int sem_count = { LTTNG_UST_INIT_SEM_COUNT }; /* * Counting nesting within lttng-ust. Used to ensure that calling fork() @@ -1922,7 +1924,7 @@ void lttng_ust_cleanup(int exiting) exit_tracepoint(); if (!exiting) { /* Reinitialize values for fork */ - sem_count = 2; + sem_count = LTTNG_UST_INIT_SEM_COUNT; lttng_ust_comm_should_quit = 0; initialized = 0; } @@ -2072,3 +2074,26 @@ void lttng_ust_sockinfo_session_enabled(void *owner) struct sock_info *sock_info = owner; sock_info->statedump_pending = 1; } + +/* + * Re-register the application when changing user ID. This is especially + * important for per-UID buffers. It is not strictly needed for per-PID + * buffers, but a slight extra overhead when changing user ID is considered + * harmless for a relatively infrequent operation. + */ +void ust_after_setuid(void) +{ + DBG("Unregistering the process"); + lttng_ust_fixup_tls(); + lttng_ust_exit(); + + sem_count = LTTNG_UST_INIT_SEM_COUNT; + lttng_ust_comm_should_quit = 0; + initialized = 0; + + global_apps.wait_shm_mmap = NULL; + local_apps.wait_shm_mmap = NULL; + + DBG("Registering the process under new UID=%u", getuid()); + lttng_ust_init(); +} -- 2.21.0