Helper functions needed to secure the promiscuous mode.

The jack_group2gid() function does a thread-safe lookup of a unix gid from a
unix group name.

The jack_promiscuous_perms() function adjusts the permissions of a shared
resource (socket, semaphore, shm segment, ...) referenced by a fd and/or a
path so it can be used by any member of the provided unix group.

By using those functions it will be possible to enable a secure promiscuous
mode. 'Secure' meaning here that one is not forced to launch every clients
with a (way) too permissive 0000 umask.

common/promiscuous.c

@@ -0,0 +1,95 @@
+/*
+ Copyright (C) 2014-2017 Cédric Schieli
+
+ This program is free software; you can redistribute it and/or
+ modify it under the terms of the GNU General Public License
+ as published by the Free Software Foundation; either version 2
+ of the License, or (at your option) any later version.
+
+ This program 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 General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+*/
+
+#ifndef WIN32
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <grp.h>
+#ifdef __APPLE__
+#include <AvailabilityMacros.h>
+#endif
+#include "JackError.h"
+#endif
+
+
+int
+jack_group2gid(const char* group)
+{
+#ifdef WIN32
+    return -1;
+#else
+    size_t buflen;
+    char *buf;
+    int ret;
+    struct group grp;
+    struct group *result;
+
+    if (!group || !*group)
+        return -1;
+
+    ret = strtol(group, &buf, 10);
+    if (!*buf)
+        return ret;
+
+/* MacOSX only defines _SC_GETGR_R_SIZE_MAX starting from 10.4 */
+#if defined(__APPLE__) && MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_4
+    buflen = 4096;
+#else
+    buflen = sysconf(_SC_GETGR_R_SIZE_MAX);
+    if (buflen == -1)
+        buflen = 4096;
+#endif
+    buf = (char*)malloc(buflen);
+
+    while (buf && ((ret = getgrnam_r(group, &grp, buf, buflen, &result)) == ERANGE)) {
+        buflen *= 2;
+        buf = (char*)realloc(buf, buflen);
+    }
+    if (!buf)
+        return -1;
+    free(buf);
+    if (ret || !result)
+        return -1;
+    return grp.gr_gid;
+#endif
+}
+
+#ifndef WIN32
+int
+jack_promiscuous_perms(int fd, const char* path, gid_t gid)
+{
+	mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;
+	if (gid >= 0) {
+		if (((fd < 0) ? chown(path, -1, gid) : fchown(fd, -1, gid)) < 0) {
+			jack_log("Cannot chgrp %s: %s. Falling back to permissive perms.", path, strerror(errno));
+		} else {
+			mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;
+		}
+	}
+	if (((fd < 0) ? chmod(path, mode) : fchmod(fd, mode)) < 0) {
+		jack_log("Cannot chmod %s: %s. Falling back to default (umask) perms.", path, strerror(errno));
+		return -1;
+	}
+	return 0;
+}
+#endif

common/promiscuous.h

@@ -0,0 +1,39 @@
+/*
+ Copyright (C) 2014-2017 Cédric Schieli
+
+ This program is free software; you can redistribute it and/or
+ modify it under the terms of the GNU General Public License
+ as published by the Free Software Foundation; either version 2
+ of the License, or (at your option) any later version.
+
+ This program 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 General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+*/
+
+#ifndef __jack_gid_h__
+#define __jack_gid_h__
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+int jack_group2gid (const char *group); /*!< Lookup gid for a UNIX group in a thread-safe way */
+#ifndef WIN32
+int jack_promiscuous_perms (int fd, const char *path, gid_t gid); /*!< Set promiscuous permissions on object referenced by fd and/or path */
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __jack_gid_h__ */
+
+

common/wscript

@@ -82,6 +82,7 @@ def build(bld):
         common_libsources += [
             'JackDebugClient.cpp',
             'timestamps.c',
+            'promiscuous.c',
             '../posix/JackPosixThread.cpp',
             '../posix/JackPosixProcessSync.cpp',
             '../posix/JackPosixMutex.cpp',
@@ -97,6 +98,7 @@ def build(bld):
         common_libsources += [
             'JackDebugClient.cpp',
             'timestamps.c',
+            'promiscuous.c',
            '../posix/JackPosixThread.cpp',
            '../posix/JackFifo.cpp',
            '../posix/JackPosixProcessSync.cpp',
@@ -111,6 +113,7 @@ def build(bld):
         common_libsources += [
             'JackDebugClient.cpp',
             'timestamps.c',
+            'promiscuous.c',
             '../posix/JackPosixProcessSync.cpp',
             '../posix/JackPosixThread.cpp',
             '../posix/JackPosixMutex.cpp',