+++ /dev/null
-/*
- * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
- * Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- *
- * SPDX-License-Identifier: GPL-2.0-only
- *
- */
-
-#define _LGPL_SOURCE
-#include <fcntl.h>
-#include <limits.h>
-#include <sys/mman.h>
-#include <sys/stat.h>
-#include <sys/types.h>
-#include <sys/wait.h>
-#include <unistd.h>
-#include <urcu.h>
-
-#include <common/error.h>
-
-#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
- * 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
- * starts.
- */
-static int get_wait_shm(char *shm_path, size_t mmap_size, int global)
-{
- int wait_shm_fd, ret;
- mode_t mode;
-
- LTTNG_ASSERT(shm_path);
-
- /* Default permissions */
- mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;
-
- /*
- * Change owner of the shm path.
- */
- if (global) {
- /*
- * If global session daemon, any application can
- * register. Make it initially writeable so applications
- * registering concurrently can do ftruncate() by
- * themselves.
- */
- mode |= S_IROTH | S_IWOTH;
- }
-
- /*
- * We're alone in a child process, so we can modify the process-wide
- * umask.
- */
- umask(~mode);
-
- /*
- * Try creating shm (or get rw access). We don't do an exclusive open,
- * because we allow other processes to create+ftruncate it concurrently.
- *
- * A sysctl, fs.protected_regular may prevent the session daemon from
- * opening a previously created shm when the O_CREAT flag is provided.
- * Systemd enables this ABI-breaking change by default since v241.
- *
- * First, attempt to use the create-or-open semantic that is
- * desired here. If this fails with EACCES, work around this broken
- * behaviour and attempt to open the shm without the O_CREAT flag.
- *
- * The two attempts are made in this order since applications are
- * expected to race with the session daemon to create this shm.
- * Attempting an shm_open() without the O_CREAT flag first could fail
- * because the file doesn't exist. It could then be created by an
- * application, which would cause a second try with the O_CREAT flag to
- * fail with EACCES.
- *
- * Note that this introduces a new failure mode where a user could
- * launch an application (creating the shm) and unlink the shm while
- * the session daemon is launching, causing the second attempt
- * to fail. This is not recovered-from as unlinking the shm will
- * prevent userspace tracing from succeeding anyhow: the sessiond would
- * use a now-unlinked shm, while the next application would create
- * a new named shm.
- */
- wait_shm_fd = shm_open(shm_path, O_RDWR | O_CREAT, mode);
- if (wait_shm_fd < 0) {
- if (errno == EACCES) {
- /* Work around sysctl fs.protected_regular. */
- DBG("shm_open of %s returned EACCES, this may be caused "
- "by the fs.protected_regular sysctl. "
- "Attempting to open the shm without "
- "creating it.", shm_path);
- wait_shm_fd = shm_open(shm_path, O_RDWR, mode);
- }
- if (wait_shm_fd < 0) {
- PERROR("Failed to open \"wait\" shared memory object: path = '%s'", shm_path);
- goto error;
- }
- }
-
- ret = ftruncate(wait_shm_fd, mmap_size);
- if (ret < 0) {
- PERROR("Failed to truncate \"wait\" shared memory object: fd = %d, size = %zu",
- wait_shm_fd, mmap_size);
- exit(EXIT_FAILURE);
- }
-
- if (global) {
- ret = fchown(wait_shm_fd, 0, 0);
- 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);
- }
- /*
- * If global session daemon, any application can
- * register so the shm needs to be set in read-only mode
- * for others.
- */
- mode &= ~S_IWOTH;
- ret = fchmod(wait_shm_fd, mode);
- 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);
- }
- } 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);
- }
- }
-
- DBG("Wait shared memory file descriptor created successfully: path = '%s', mmap_size = %zu, global = %s, fd = %d",
- shm_path, mmap_size, global ? "true" : "false",
- wait_shm_fd);
-
- 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");
-
- return -1;
-}
-
-/*
- * Return the wait shm mmap for UST application notification. The global
- * variable is used to indicate if the the session daemon is global
- * (root:tracing) or running with an unprivileged user.
- *
- * This returned value is used by futex_wait_update() in futex.c to WAKE all
- * waiters which are UST application waiting for a session daemon.
- */
-char *shm_ust_get_mmap(char *shm_path, int global)
-{
- size_t mmap_size;
- int wait_shm_fd, ret;
- char *wait_shm_mmap;
- long sys_page_size;
-
- LTTNG_ASSERT(shm_path);
-
- sys_page_size = sysconf(_SC_PAGE_SIZE);
- if (sys_page_size < 0) {
- PERROR("Failed to get PAGE_SIZE of system");
- goto error;
- }
- mmap_size = sys_page_size;
-
- wait_shm_fd = get_wait_shm(shm_path, mmap_size, global);
- if (wait_shm_fd < 0) {
- goto error;
- }
-
- wait_shm_mmap = mmap(NULL, mmap_size, PROT_WRITE | PROT_READ,
- MAP_SHARED, wait_shm_fd, 0);
-
- /* close shm fd immediately after taking the mmap reference */
- ret = close(wait_shm_fd);
- if (ret) {
- PERROR("Failed to close \"wait\" shared memory object file descriptor: fd = %d",
- wait_shm_fd);
- }
-
- if (wait_shm_mmap == MAP_FAILED) {
- DBG("Failed to mmap the \"wait\" shareed memory object (can be caused by race with ust): path = '%s', global = %s",
- shm_path, global ? "true" : "false");
- goto error;
- }
-
- return wait_shm_mmap;
-
-error:
- return NULL;
-}
-
-/*
- * shm_create_anonymous is never called concurrently within a process.
- */
-int shm_create_anonymous(const char *owner_name)
-{
- char tmp_name[NAME_MAX];
- int shmfd, ret;
-
- ret = snprintf(tmp_name, NAME_MAX, "/shm-%s-%d", owner_name, getpid());
- if (ret < 0) {
- PERROR("Failed to format shm path: owner_name = '%s', pid = %d",
- owner_name, getpid());
- return -1;
- }
-
- /*
- * Allocate shm, and immediately unlink its shm oject, keeping only the
- * file descriptor as a reference to the object.
- */
- shmfd = shm_open(tmp_name, O_CREAT | O_EXCL | O_RDWR, 0700);
- if (shmfd < 0) {
- PERROR("Failed to open shared memory object: path = '%s'", tmp_name);
- goto error_shm_open;
- }
-
- ret = shm_unlink(tmp_name);
- if (ret < 0 && errno != ENOENT) {
- PERROR("Failed to unlink shared memory object: path = '%s'",
- tmp_name);
- goto error_shm_release;
- }
-
- return shmfd;
-
-error_shm_release:
- ret = close(shmfd);
- if (ret) {
- PERROR("Failed to close shared memory object file descriptor: fd = %d, path = '%s'",
- shmfd, tmp_name);
- }
-error_shm_open:
- return -1;
-}
projects / lttng-tools.git / blobdiff