[lttng-dev] [lttng-ust RFC] Add setuid wrapper for per-UID buffers

[Sebastien Boisvert]

On 2019-05-21 2:01 p.m., Gabriel-Andrew Pollo-Guilbert wrote:
> In case of a per-UID buffers, events following a setuid() call should be
> fowarded 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 <gabriel.pollo-guilbert at efficios.com>
> ---
>  Makefile.am                     |  1 +
>  configure.ac                    |  1 +
>  include/lttng/ust.h             |  1 +
>  liblttng-ust-setuid/Makefile.am | 10 +++++++
>  liblttng-ust-setuid/ustsetuid.c | 48 +++++++++++++++++++++++++++++++++
>  liblttng-ust/lttng-ust-comm.c   | 23 ++++++++++++++++
>  6 files changed, 84 insertions(+)
>  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/include/lttng/ust.h b/include/lttng/ust.h
> index 2779d7a7..37f15520 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();
>  
>  #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..f95e1896
> --- /dev/null
> +++ b/liblttng-ust-setuid/ustsetuid.c
> @@ -0,0 +1,48 @@
> +/*
> + * 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 <lttng/ust-dlfcn.h>
> +#include <unistd.h>
> +#include <errno.h>
> +#include <stdio.h>
> +
> +#include <lttng/ust.h>

I think that you can move this include right after the other lttng include above.

> +
> +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..5e55466e 100644
> --- a/liblttng-ust/lttng-ust-comm.c
> +++ b/liblttng-ust/lttng-ust-comm.c
> @@ -2072,3 +2072,26 @@ void lttng_ust_sockinfo_session_enabled(void *owner)
>  	struct sock_info *sock_info = owner;
>  	sock_info->statedump_pending = 1;
>  }
> +
> +void ust_after_setuid()
> +{
> +	/*
> +	 * TODO: Don't re-register the application if in per-PID mode. That
> +	 *       said, LTTng-UST isn't aware of the buffer types configured by
> +	 *       LTTng-Tools.
> +	 */
> +
> +	DBG("Unregistering the process");
> +	lttng_ust_fixup_tls();
> +	lttng_ust_exit();
> +
> +	sem_count = 2;
> +	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();

Can any of those function calls fail ?

> +}
>