From e9fed2438a1ff475821864f906286dc58907f06b Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Wed, 3 Feb 2021 08:55:13 -0300 Subject: linux: Require /dev/shm as the shared memory file system Previously, glibc would pick an arbitrary tmpfs file system from /proc/mounts if /dev/shm was not available. This could lead to an unsuitable file system being picked for the backing storage for shm_open, sem_open, and related functions. This patch introduces a new function, __shm_get_name, which builds the file name under the appropriate (now hard-coded) directory. It is called from the various shm_* and sem_* function. Unlike the SHM_GET_NAME macro it replaces, the callers handle the return values and errno updates. shm-directory.c is moved directly into the posix subdirectory because it can be implemented directly using POSIX functionality. It resides in libc because it is needed by both librt and nptl/htl. In the sem_open implementation, tmpfname is initialized directly from a string constant. This happens to remove one alloca call. Checked on x86_64-linux-gnu. --- include/shm-directory.h | 41 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) create mode 100644 include/shm-directory.h (limited to 'include') diff --git a/include/shm-directory.h b/include/shm-directory.h new file mode 100644 index 0000000000..1d3ffb6137 --- /dev/null +++ b/include/shm-directory.h @@ -0,0 +1,41 @@ +/* Header for directory for shm/sem files. + Copyright (C) 2014-2021 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C 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; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C 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 the GNU C Library; if not, see + . */ + +#ifndef _SHM_DIRECTORY_H + +#include +#include +#include + +/* The directory that contains shared POSIX objects. */ +#define SHMDIR _PATH_DEV "shm/" + +struct shmdir_name +{ + /* The combined prefix/name. The sizeof includes the terminating + NUL byte. 4 bytes are needed for the optional "sem." prefix. */ + char name[sizeof (SHMDIR) + 4 + NAME_MAX]; +}; + +/* Sets RESULT->name to the constructed name and returns 0 on success, + or -1 on failure. Includes the "sem." prefix in the name if + SEM_PREFIX is true. */ +int __shm_get_name (struct shmdir_name *result, const char *name, + bool sem_prefix); + +#endif /* shm-directory.h */ -- cgit v1.2.3-70-g09d2