[lttng-dev] [lttng-ust RFC v3] Add setuid wrappers for per-UID buffers
Gabriel-Andrew Pollo-Guilbert
gabriel.pollo-guilbert at efficios.com
Mon May 27 17:51:01 EDT 2019
In case of a per-UID buffer, events following a change of user ID should be
forwarded to buffers of the new UID. In order to do so, we add a wrapper around
setuid(3), setreuid(3) and setresuid(2) that unregister and re-register the
application from the session daemon.
While there exist some other functions such as seteuid(3) or setfsuid(2), we
don't need to add a wrapper for them since they do not edit the real user ID,
the actual ID returned by getuid(3) and used for creating the buffers.
Signed-off-by: Gabriel-Andrew Pollo-Guilbert <gabriel.pollo-guilbert at efficios.com>
---
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 | 102 ++++++++++++++++++++++++++++++++
liblttng-ust/lttng-ust-comm.c | 29 ++++++++-
7 files changed, 153 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..b94ea8d2
--- /dev/null
+++ b/liblttng-ust-setuid/ustsetuid.c
@@ -0,0 +1,102 @@
+/*
+ * 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 <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+#include <lttng/ust-dlfcn.h>
+#include <lttng/ust.h>
+
+int setuid(uid_t uid)
+{
+ static int (*plibc_func)(uid_t) = NULL;
+ int retval;
+
+ if (plibc_func == NULL) {
+ plibc_func = dlsym(RTLD_NEXT, __func__);
+ if (plibc_func == NULL) {
+ fprintf(stderr, "libustsetuid: unable to find \"%s\" symbol\n", __func__);
+ errno = ENOSYS;
+ return -1;
+ }
+ }
+
+ uid_t before_uid = getuid();
+
+ retval = plibc_func(uid);
+ if (retval < 0)
+ return retval;
+
+ if (before_uid != getuid())
+ ust_after_setuid();
+
+ return retval;
+}
+
+int setreuid(uid_t ruid, uid_t euid)
+{
+ static int (*plibc_func)(uid_t, uid_t) = NULL;
+ int retval;
+
+ if (plibc_func == NULL) {
+ plibc_func = dlsym(RTLD_NEXT, __func__);
+ if (plibc_func == NULL) {
+ fprintf(stderr, "libustsetuid: unable to find \"%s\" symbol\n", __func__);
+ errno = ENOSYS;
+ return -1;
+ }
+ }
+
+ uid_t before_uid = getuid();
+
+ retval = plibc_func(ruid, euid);
+ if (retval < 0)
+ return retval;
+
+ if (before_uid != getuid())
+ ust_after_setuid();
+
+ return retval;
+}
+
+int setresuid(uid_t ruid, uid_t euid, uid_t suid)
+{
+ static int (*plibc_func)(uid_t, uid_t, uid_t) = NULL;
+ int retval;
+
+ if (plibc_func == NULL) {
+ plibc_func = dlsym(RTLD_NEXT, __func__);
+ if (plibc_func == NULL) {
+ fprintf(stderr, "libustsetuid: unable to find \"%s\" symbol\n", __func__);
+ errno = ENOSYS;
+ return -1;
+ }
+ }
+
+ uid_t before_uid = getuid();
+
+ retval = plibc_func(ruid, euid, suid);
+ if (retval < 0)
+ return retval;
+
+ if (before_uid != getuid())
+ 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
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