Support creds passing between lttng and sessiond

From now on, the lttng command line sends it's credential at each
command along with the regular communication data.

The tracing output directory is set to those credentials (uid/gid) if
the session daemon is running as a regular user (even if the user is in
the tracing group). So *no* tracing group is ever set if the session
daemon is not running as a non-root user.

If the sessiond is running as root, the tracing group is set (if exist)
and the uid of the calling user is used.

This fixes the triple enable-channel/event needed to trace UST
applications with a non-root session daemon. This was reported by
Yannick Brosseau <yannick.brosseau@polymtl.ca>.

Signed-off-by: David Goulet <david.goulet@polymtl.ca>

diff --git a/liblttngctl/lttngctl.c b/liblttngctl/lttngctl.c
index c5e8cf8f8cffae86ecce900354f13a0752b4e382..c65760155347d4ca7e576ea7b24132b580d47e7f 100644 (file)
--- a/liblttngctl/lttngctl.c
+++ b/liblttngctl/lttngctl.c
@@ -93,7 +93,7 @@ static int send_session_msg(struct lttcomm_session_msg *lsm)
                goto end;
        }
 
-       ret = lttcomm_send_unix_sock(sessiond_socket, lsm,
+       ret = lttcomm_send_creds_unix_sock(sessiond_socket, lsm,
                        sizeof(struct lttcomm_session_msg));
 
 end:

diff --git a/lttng-sessiond/event.c b/lttng-sessiond/event.c
index 6e247aa9139db8cf5fcabff7b55810886c47f719..90b10ec3a64e6b4b5defa62e2ccc3a17f22df225 100644 (file)
--- a/lttng-sessiond/event.c
+++ b/lttng-sessiond/event.c
@@ -15,6 +15,7 @@
  * Place - Suite 330, Boston, MA  02111-1307, USA.
  */
 
+#define _GNU_SOURCE
 #include <errno.h>
 #include <urcu/list.h>
 #include <string.h>

diff --git a/lttng-sessiond/lttng-sessiond.h b/lttng-sessiond/lttng-sessiond.h
index 63de2e12076ac3509f049062b2d7bfd60786d9b1..7de024f805136061e8f9c503fa699e7fec1c68aa 100644 (file)
--- a/lttng-sessiond/lttng-sessiond.h
+++ b/lttng-sessiond/lttng-sessiond.h
@@ -71,6 +71,7 @@ extern const char default_home_dir[],
 struct command_ctx {
        int ust_sock;
        unsigned int lttng_msg_size;
+       struct ucred creds;
        struct ltt_session *session;
        struct lttcomm_lttng_msg *llm;
        struct lttcomm_session_msg *lsm;

diff --git a/lttng-sessiond/main.c b/lttng-sessiond/main.c
index 7d63656e4c401b9d66037d2c9d8126974cf6f4c5..25a8ca76bbcb771b8ec309708534ccfddeb03c49 100644 (file)
--- a/lttng-sessiond/main.c
+++ b/lttng-sessiond/main.c
@@ -1871,10 +1871,11 @@ error:
  * Create an UST session and add it to the session ust list.
  */
 static int create_ust_session(struct ltt_session *session,
-               struct lttng_domain *domain)
+               struct lttng_domain *domain, struct ucred *creds)
 {
        int ret;
-       unsigned int uid;
+       unsigned int sess_uid;
+       gid_t gid;
        struct ltt_ust_session *lus = NULL;
 
        switch (domain->type) {
@@ -1887,15 +1888,23 @@ static int create_ust_session(struct ltt_session *session,
 
        DBG("Creating UST session");
 
-       uid = session->uid;
-       lus = trace_ust_create_session(session->path, uid, domain);
+       sess_uid = session->uid;
+       lus = trace_ust_create_session(session->path, sess_uid, domain);
        if (lus == NULL) {
                ret = LTTCOMM_UST_SESS_FAIL;
                goto error;
        }
 
-       ret = mkdir_recursive(lus->pathname, S_IRWXU | S_IRWXG,
-                       geteuid(), allowed_group());
+       /*
+        * Get the right group ID. To use the tracing group, the daemon must be
+        * running with root credentials or else it's the user GID used.
+        */
+       gid = allowed_group();
+       if (gid < 0 || !is_root) {
+               gid = creds->gid;
+       }
+
+       ret = mkdir_recursive(lus->pathname, S_IRWXU | S_IRWXG, creds->uid, gid);
        if (ret < 0) {
                if (ret != -EEXIST) {
                        ERR("Trace directory creation error");
@@ -1925,9 +1934,11 @@ error:
 /*
  * Create a kernel tracer session then create the default channel.
  */
-static int create_kernel_session(struct ltt_session *session)
+static int create_kernel_session(struct ltt_session *session,
+               struct ucred *creds)
 {
        int ret;
+       gid_t gid;
 
        DBG("Creating kernel session");
 
@@ -1942,8 +1953,17 @@ static int create_kernel_session(struct ltt_session *session)
                session->kernel_session->consumer_fd = kconsumer_data.cmd_sock;
        }
 
+       gid = allowed_group();
+       if (gid < 0) {
+               /*
+                * Use GID 0 has a fallback since kernel session is only allowed under
+                * root or the gid of the calling user
+                */
+               is_root ? (gid = 0) : (gid = creds->gid);
+       }
+
        ret = mkdir_recursive(session->kernel_session->trace_path,
-                       S_IRWXU | S_IRWXG, geteuid(), allowed_group());
+                       S_IRWXU | S_IRWXG, creds->uid, gid);
        if (ret < 0) {
                if (ret != -EEXIST) {
                        ERR("Trace directory creation error");
@@ -3234,7 +3254,7 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
                /* Need a session for kernel command */
                if (need_tracing_session) {
                        if (cmd_ctx->session->kernel_session == NULL) {
-                               ret = create_kernel_session(cmd_ctx->session);
+                               ret = create_kernel_session(cmd_ctx->session, &cmd_ctx->creds);
                                if (ret < 0) {
                                        ret = LTTCOMM_KERN_SESS_FAIL;
                                        goto error;
@@ -3261,7 +3281,7 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
                if (need_tracing_session) {
                        if (cmd_ctx->session->ust_session == NULL) {
                                ret = create_ust_session(cmd_ctx->session,
-                                               &cmd_ctx->lsm->domain);
+                                               &cmd_ctx->lsm->domain, &cmd_ctx->creds);
                                if (ret != LTTCOMM_OK) {
                                        goto error;
                                }
@@ -3628,6 +3648,12 @@ static void *thread_manage_clients(void *data)
                        goto error;
                }
 
+               /* Set socket option for credentials retrieval */
+               ret = lttcomm_setsockopt_creds_unix_sock(sock);
+               if (ret < 0) {
+                       goto error;
+               }
+
                /* Allocate context command to process the client request */
                cmd_ctx = zmalloc(sizeof(struct command_ctx));
                if (cmd_ctx == NULL) {
@@ -3651,8 +3677,8 @@ static void *thread_manage_clients(void *data)
                 * the client.
                 */
                DBG("Receiving data from client ...");
-               ret = lttcomm_recv_unix_sock(sock, cmd_ctx->lsm,
-                               sizeof(struct lttcomm_session_msg));
+               ret = lttcomm_recv_creds_unix_sock(sock, cmd_ctx->lsm,
+                               sizeof(struct lttcomm_session_msg), &cmd_ctx->creds);
                if (ret <= 0) {
                        DBG("Nothing recv() from client... continuing");
                        close(sock);
@@ -3690,10 +3716,10 @@ static void *thread_manage_clients(void *data)
                        ERR("Failed to send data back to client");
                }
 
-               clean_command_ctx(&cmd_ctx);
-
                /* End of transmission */
                close(sock);
+
+               clean_command_ctx(&cmd_ctx);
        }
 
 error:
@@ -3935,27 +3961,22 @@ static int check_existing_daemon(void)
  * Race window between mkdir and chown is OK because we are going from more
  * permissive (root.root) to les permissive (root.tracing).
  */
-static int set_permissions(void)
+static int set_permissions(char *rundir)
 {
        int ret;
        gid_t gid;
 
        gid = allowed_group();
        if (gid < 0) {
-               if (is_root) {
-                       WARN("No tracing group detected");
-                       ret = 0;
-               } else {
-                       ERR("Missing tracing group. Aborting execution.");
-                       ret = -1;
-               }
+               WARN("No tracing group detected");
+               ret = 0;
                goto end;
        }
 
        /* Set lttng run dir */
-       ret = chown(LTTNG_RUNDIR, 0, gid);
+       ret = chown(rundir, 0, gid);
        if (ret < 0) {
-               ERR("Unable to set group on " LTTNG_RUNDIR);
+               ERR("Unable to set group on %s", rundir);
                perror("chown");
        }
 
@@ -4367,7 +4388,7 @@ int main(int argc, char **argv)
        }
 
        /* Set credentials to socket */
-       if (is_root && ((ret = set_permissions()) < 0)) {
+       if (is_root && ((ret = set_permissions(rundir)) < 0)) {
                goto exit;
        }