X-Git-Url: http://git.efficios.com/?p=lttng-tools.git;a=blobdiff_plain;f=src%2Fbin%2Flttng-sessiond%2Fshm.c;fp=src%2Fbin%2Flttng-sessiond%2Fshm.c;h=0000000000000000000000000000000000000000;hp=1fc07dbd3915fec4606139cdee3bf1012b4edba9;hb=2463b7879c00298daa79744cdaae82ac061a4ed8;hpb=3a4595c2469472dee1656cde5f8882c2123efd3c diff --git a/src/bin/lttng-sessiond/shm.c b/src/bin/lttng-sessiond/shm.c deleted file mode 100644 index 1fc07dbd3..000000000 --- a/src/bin/lttng-sessiond/shm.c +++ /dev/null @@ -1,195 +0,0 @@ -/* - * Copyright (C) 2011 David Goulet - * Copyright (C) 2011 Mathieu Desnoyers - * - * SPDX-License-Identifier: GPL-2.0-only - * - */ - -#define _LGPL_SOURCE -#include -#include -#include -#include -#include -#include -#include -#include - -#include - -#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; - - 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 shm at %s", shm_path); - goto error; - } - } - - ret = ftruncate(wait_shm_fd, mmap_size); - if (ret < 0) { - PERROR("ftruncate wait shm"); - exit(EXIT_FAILURE); - } - -#ifndef __FreeBSD__ - if (global) { - ret = fchown(wait_shm_fd, 0, 0); - if (ret < 0) { - PERROR("fchown"); - 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("fchmod"); - exit(EXIT_FAILURE); - } - } else { - ret = fchown(wait_shm_fd, getuid(), getgid()); - if (ret < 0) { - PERROR("fchown"); - exit(EXIT_FAILURE); - } - } -#else -#warning "FreeBSD does not support setting file mode on shm FD." -#endif - - DBG("Got the wait shm fd %d", wait_shm_fd); - - return wait_shm_fd; - -error: - DBG("Failing to get the wait shm fd"); - - 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; - - assert(shm_path); - - sys_page_size = sysconf(_SC_PAGE_SIZE); - if (sys_page_size < 0) { - PERROR("sysconf PAGE_SIZE"); - 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("Error closing fd"); - } - - if (wait_shm_mmap == MAP_FAILED) { - DBG("mmap error (can be caused by race with ust)."); - goto error; - } - - return wait_shm_mmap; - -error: - return NULL; -}