qemu: ensure sane umask for qemu process

Add umask to _virCommand, allow user to set umask to command.
Set umask(002) to qemu process to overwrite the default umask
of 022 set by many distros, so that unix sockets created for
virtio-serial has expected permissions.

Fix problem reported here:
https://sourceware.org/bugzilla/show_bug.cgi?id=13078#c11
https://bugzilla.novell.com/show_bug.cgi?id=888166

To use virtio-serial device, unix socket created for chardev with
default umask(022) has insufficient permissions.
e.g.:
-device virtio-serial \
-chardev socket,path=/tmp/foo,server,nowait,id=foo \
-device virtserialport,chardev=foo,name=org.fedoraproject.port.0

srwxr-xr-x 1 qemu qemu 0 21. Jul 14:19 /tmp/somefile.sock

Other users in the same group (like real user, test engines, etc)
cannot write to this socket.
Signed-off-by: NChunyan Liu <cyliu@suse.com>
Signed-off-by: NEric Blake <eblake@redhat.com>

src/libvirt_private.syms

@@ -1171,6 +1171,7 @@ virCommandSetPidFile;
 virCommandSetPreExecHook;
 virCommandSetSELinuxLabel;
 virCommandSetUID;
+virCommandSetUmask;
 virCommandSetWorkingDirectory;
 virCommandToString;
 virCommandWait;

src/qemu/qemu_process.c

@@ -4141,6 +4141,7 @@ int qemuProcessStart(virConnectPtr conn,
     virCommandSetPreExecHook(cmd, qemuProcessHook, &hookData);
     virCommandSetMaxProcesses(cmd, cfg->maxProcesses);
     virCommandSetMaxFiles(cmd, cfg->maxFiles);
+    virCommandSetUmask(cmd, 0x002);
 
     VIR_DEBUG("Setting up security labelling");
     if (virSecurityManagerSetChildProcessLabel(driver->securityManager,

src/util/vircommand.c

@@ -133,6 +133,7 @@ struct _virCommand {
 #if defined(WITH_SECDRIVER_APPARMOR)
     char *appArmorProfile;
 #endif
+    int umask;
 };
 
 /* See virCommandSetDryRun for description for this variable */
@@ -582,6 +583,8 @@ virExec(virCommandPtr cmd)
 
     /* child */
 
+    if (cmd->umask)
+        umask(cmd->umask);
     ret = EXIT_CANCELED;
     openmax = sysconf(_SC_OPEN_MAX);
     if (openmax < 0) {
@@ -1082,6 +1085,14 @@ virCommandSetMaxFiles(virCommandPtr cmd, unsigned int files)
     cmd->maxFiles = files;
 }
 
+void virCommandSetUmask(virCommandPtr cmd, int umask)
+{
+    if (!cmd || cmd->has_error)
+        return;
+
+    cmd->umask = umask;
+}
+
 /**
  * virCommandClearCaps:
  * @cmd: the command to modify

src/util/vircommand.h

@@ -72,6 +72,7 @@ void virCommandSetUID(virCommandPtr cmd, uid_t uid);
 void virCommandSetMaxMemLock(virCommandPtr cmd, unsigned long long bytes);
 void virCommandSetMaxProcesses(virCommandPtr cmd, unsigned int procs);
 void virCommandSetMaxFiles(virCommandPtr cmd, unsigned int files);
+void virCommandSetUmask(virCommandPtr cmd, int umask);
 
 void virCommandClearCaps(virCommandPtr cmd);