Fix: agent port file is o+w when launching as root

Observed issue
==============

When starting as root, the following permissions are observed:

[-rw-rw-rw-]  agent.port
[-rw-r--r--]  lttng-sessiond.pid

When starting as user:

[-rw-rw----]  agent.port
[-rw-rw-r--]  lttng-sessiond.pid

Note that despite being created by the same function,
`utils_create_pid_file`, the permissions are not the same.

Cause
=====

`get_wait_shm` manipulates the umask and does not restore it, thus
influencing the outcome of following file creations that don't enforce
specific permissions (using chmod).

Also `fopen` defaults to mode `0666 & ~umask`, thus resulting in
unnecessarily lax permissions when the session daemon is started as a
non-privileged user (umask = 0002, most of the time).

Solution
========

Mimic other call sites of umask(), modify then revert the umask.

Open the pid and agent port files as 0644 letting the umask to do its
job as necessary for those files.

Remove unnecessary umask() usage when chmod is directly used.

Known drawbacks
===============

Use of umask in a multi-threaded process is not recommended. Still our
current usage is limited and mostly happens during the initialization
phase. The usage of umask() is required for the `wait_shm` since on
FreeBSD it is not possible to chmod an shm file descriptor. The default
umask would interfere here.

Discussion
==========

The usage in run-as is valid even when in no-clone mode (valgrind) since
it is the sole user of umask() following the initialization phase. When
spawned as a separate process the clearing of umask is totally valid
even if it is not ideal since we are ignoring any umask set by the user.

It seems like the current usage is the lesser evil here.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Ie224d254714fff05f4bced471ebfa8f19eede26a

diff --git a/src/bin/lttng-sessiond/client.c b/src/bin/lttng-sessiond/client.c
index 9873a8f0c9971e23c1c304b92b3d20013d3dd442..a3d508a7018d5df82c0f0157ec7ba43fd1b5479a 100644 (file)
--- a/src/bin/lttng-sessiond/client.c
+++ b/src/bin/lttng-sessiond/client.c
@@ -2395,7 +2395,6 @@ init_setup_error:
 static int create_client_sock(void)
 {
        int ret, client_sock;
-       const mode_t old_umask = umask(0);
 
        /* Create client tool unix socket */
        client_sock = lttcomm_create_unix_sock(
@@ -2429,7 +2428,6 @@ static int create_client_sock(void)
        DBG("Created client socket (fd = %i)", client_sock);
        ret = client_sock;
 end:
-       umask(old_umask);
        return ret;
 }
 

diff --git a/src/bin/lttng-sessiond/register.c b/src/bin/lttng-sessiond/register.c
index c8052d2c154b6ac5c369eb227fd2e8d68e5105fb..334ed9dff6c936001a38dd952f1231f0592a2156 100644 (file)
--- a/src/bin/lttng-sessiond/register.c
+++ b/src/bin/lttng-sessiond/register.c
@@ -39,7 +39,6 @@ static int create_application_socket(void)
 {
        int ret = 0;
        int apps_sock;
-       const mode_t old_umask = umask(0);
 
        /* Create the application unix socket */
        apps_sock = lttcomm_create_unix_sock(
@@ -72,7 +71,6 @@ static int create_application_socket(void)
        DBG3("Session daemon application socket created (fd = %d) ", apps_sock);
        ret = apps_sock;
 end:
-       umask(old_umask);
        return ret;
 error_close_socket:
        if (close(apps_sock)) {

diff --git a/src/common/shm.c b/src/common/shm.c
index 49fd719783ab9e291210b307d89c37a8a8b00533..a6497850c6b53bf783705ff2a256137c350f568a 100644 (file)
--- a/src/common/shm.c
+++ b/src/common/shm.c
@@ -21,8 +21,7 @@
 #include "shm.h"
 
 /*
- * Using fork to set umask in the child process (not multi-thread safe). We
- * deal with the shm_open vs ftruncate race (happening when the sessiond owns
+ * We deal with the shm_open vs ftruncate race (happening when the sessiond owns
  * the shm and does not let everybody modify it, to ensure safety against
  * shm_unlink) by simply letting the mmap fail and retrying after a few
  * seconds. For global shm, everybody has rw access to it until the sessiond
@@ -31,7 +30,7 @@
 static int get_wait_shm(char *shm_path, size_t mmap_size, int global)
 {
        int wait_shm_fd, ret;
-       mode_t mode;
+       mode_t mode, old_mode;
 
        assert(shm_path);
 
@@ -51,11 +50,7 @@ static int get_wait_shm(char *shm_path, size_t mmap_size, int global)
                mode |= S_IROTH | S_IWOTH;
        }
 
-       /*
-        * We're alone in a child process, so we can modify the process-wide
-        * umask.
-        */
-       umask(~mode);
+       old_mode = umask(~mode);
 
        /*
         * Try creating shm (or get rw access). We don't do an exclusive open,
@@ -104,7 +99,7 @@ static int get_wait_shm(char *shm_path, size_t mmap_size, int global)
        if (ret < 0) {
                PERROR("Failed to truncate \"wait\" shared memory object: fd = %d, size = %zu",
                                wait_shm_fd, mmap_size);
-               exit(EXIT_FAILURE);
+               goto error;
        }
 
        if (global) {
@@ -112,7 +107,7 @@ static int get_wait_shm(char *shm_path, size_t mmap_size, int global)
                if (ret < 0) {
                        PERROR("Failed to set ownership of \"wait\" shared memory object: fd = %d, owner = 0, group = 0",
                                        wait_shm_fd);
-                       exit(EXIT_FAILURE);
+                       goto error;
                }
                /*
                 * If global session daemon, any application can
@@ -124,14 +119,14 @@ static int get_wait_shm(char *shm_path, size_t mmap_size, int global)
                if (ret < 0) {
                        PERROR("Failed to set the mode of the \"wait\" shared memory object: fd = %d, mode = %d",
                                        wait_shm_fd, mode);
-                       exit(EXIT_FAILURE);
+                       goto error;
                }
        } else {
                ret = fchown(wait_shm_fd, getuid(), getgid());
                if (ret < 0) {
                        PERROR("Failed to set ownership of \"wait\" shared memory object: fd = %d, owner = %d, group = %d",
                                        wait_shm_fd, getuid(), getgid());
-                       exit(EXIT_FAILURE);
+                       goto error;
                }
        }
 
@@ -139,13 +134,20 @@ static int get_wait_shm(char *shm_path, size_t mmap_size, int global)
                        shm_path, mmap_size, global ? "true" : "false",
                        wait_shm_fd);
 
+end:
+       (void) umask(old_mode);
        return wait_shm_fd;
 
 error:
-       DBG("Failed to open shared memory file descriptor: path = '%s', mmap_size = %zu, global = %s",
-                       shm_path, mmap_size, global ? "true" : "false");
+       DBG("Failing to get the wait shm fd");
+       if (wait_shm_fd >= 0) {
+               if (close(wait_shm_fd)) {
+                       PERROR("Failed to close wait shm file descriptor during error handling");
+               }
+       }
 
-       return -1;
+       wait_shm_fd = -1;
+       goto end;
 }
 
 /*

diff --git a/src/common/utils.c b/src/common/utils.c
index febd75c185ddd87c177f388dfb7ba464e44cbf5c..682084c0f67d0cf32eb39bb2c9e76a5975a0f559 100644 (file)
--- a/src/common/utils.c
+++ b/src/common/utils.c
@@ -224,30 +224,40 @@ end:
 LTTNG_HIDDEN
 int utils_create_pid_file(pid_t pid, const char *filepath)
 {
-       int ret;
-       FILE *fp;
+       int ret, fd = -1;
+       FILE *fp = NULL;
 
        assert(filepath);
 
-       fp = fopen(filepath, "w");
+       fd = open(filepath, O_CREAT | O_WRONLY, S_IRUSR |S_IWUSR | S_IRGRP | S_IROTH);
+       if (fd < 0) {
+               PERROR("open file %s", filepath);
+               ret = -1;
+               goto error;
+       }
+
+       fp = fdopen(fd, "w");
        if (fp == NULL) {
-               PERROR("open pid file %s", filepath);
+               PERROR("fdopen file %s", filepath);
                ret = -1;
+               close(fd);
                goto error;
        }
 
        ret = fprintf(fp, "%d\n", (int) pid);
        if (ret < 0) {
-               PERROR("fprintf pid file");
+               PERROR("fprintf file %s", filepath);
+               ret = -1;
                goto error;
        }
 
-       if (fclose(fp)) {
-               PERROR("fclose");
-       }
-       DBG("Pid %d written in file %s", (int) pid, filepath);
+       DBG("'%d' written in file %s", (int) pid, filepath);
        ret = 0;
+
 error:
+       if (fp && fclose(fp)) {
+               PERROR("fclose file %s", filepath);
+       }
        return ret;
 }