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virt-login-shell: use single instead of double fork

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Note that 'virsh lxc-enter-namespace' must double-fork, for two
reasons: some namespaces can only be done from a single thread,
while virsh is multithreaded; and because virsh can be run in
batch mode where we must not corrupt the namespace of that
execution upon return from the subsidiary command.

When virt-login-shell was first written, it blindly copied from
'virsh lxc-enter-namespace', including the double-fork.  But
neither of the reasons for double forking apply to
virt-login-shell (we are single-threaded, and we have nothing to
do after the child completes that would require us to preserve a
namespace), so we can simplify life by using a single fork.
In turn, this will make it easier for a future patch to pass the
child's exit status on to the invoking shell.

In flattening to a single fork, note that closing the fds must
be done after fork, because the parent process still needs to
use fds to control the virConnectPtr; meanwhile, chdir can be
done prior to forking (in fact, it's easier to report errors
on anything attempted before forking).

* tools/virt-login-shell.c (main): Single rather than double fork.
(virLoginShellFini): Delete, by inlining actions instead.

Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Eric Blake 2013-12-23 09:15:16 -07:00
parent 25f87817ab
commit 4594a33b4b
1 changed files with 43 additions and 73 deletions
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116
tools/virt-login-shell.c
View File

@ -41,24 +41,8 @@
#include "vircommand.h"
#define VIR_FROM_THIS VIR_FROM_NONE
static ssize_t nfdlist;
static int *fdlist;
static const char *conf_file = SYSCONFDIR "/libvirt/virt-login-shell.conf";
static void virLoginShellFini(virConnectPtr conn, virDomainPtr dom)
{
size_t i;
for (i = 0; i < nfdlist; i++)
VIR_FORCE_CLOSE(fdlist[i]);
VIR_FREE(fdlist);
nfdlist = 0;
if (dom)
virDomainFree(dom);
if (conn)
virConnectClose(conn);
}
static int virLoginShellAllowedUser(virConfPtr conf,
const char *name,
gid_t *groups)
@ -187,7 +171,6 @@ main(int argc, char **argv)
pid_t cpid;
int ret = EXIT_FAILURE;
int status;
int status2;
uid_t uid = getuid();
gid_t gid = getgid();
char *name = NULL;
@ -201,6 +184,10 @@ main(int argc, char **argv)
int longindex = -1;
int ngroups;
gid_t *groups = NULL;
ssize_t nfdlist = 0;
int *fdlist = NULL;
int openmax;
size_t i;
struct option opt[] = {
{"help", no_argument, NULL, 'h'},
@ -298,6 +285,13 @@ main(int argc, char **argv)
}
}
openmax = sysconf(_SC_OPEN_MAX);
if (openmax < 0) {
virReportSystemError(errno, "%s",
_("sysconf(_SC_OPEN_MAX) failed"));
goto cleanup;
}
if ((nfdlist = virDomainLxcOpenNamespace(dom, &fdlist, 0)) < 0)
goto cleanup;
if (VIR_ALLOC(secmodel) < 0)
@ -308,76 +302,52 @@ main(int argc, char **argv)
goto cleanup;
if (virDomainGetSecurityLabel(dom, seclabel) < 0)
goto cleanup;
if (virSetUIDGID(0, 0, NULL, 0) < 0)
goto cleanup;
if (virDomainLxcEnterSecurityLabel(secmodel, seclabel, NULL, 0) < 0)
goto cleanup;
if (nfdlist > 0 &&
virDomainLxcEnterNamespace(dom, nfdlist, fdlist, NULL, NULL, 0) < 0)
goto cleanup;
if (virSetUIDGID(uid, gid, groups, ngroups) < 0)
goto cleanup;
if (chdir(homedir) < 0) {
virReportSystemError(errno, _("Unable to chdir(%s)"), homedir);
goto cleanup;
}
/* Fork once because we don't want to affect virt-login-shell's
* namespace itself. FIXME: is this necessary?
*/
/* A fork is required to create new process in correct pid namespace. */
if ((cpid = virFork()) < 0)
goto cleanup;
if (cpid == 0) {
pid_t ccpid;
int tmpfd;
int openmax = sysconf(_SC_OPEN_MAX);
int fd;
if (virSetUIDGID(0, 0, NULL, 0) < 0)
return EXIT_FAILURE;
if (virDomainLxcEnterSecurityLabel(secmodel,
seclabel,
NULL,
0) < 0)
return EXIT_FAILURE;
if (nfdlist > 0) {
if (virDomainLxcEnterNamespace(dom,
nfdlist,
fdlist,
NULL,
NULL,
0) < 0)
return EXIT_FAILURE;
}
ret = virSetUIDGID(uid, gid, groups, ngroups);
VIR_FREE(groups);
if (ret < 0)
return EXIT_FAILURE;
if (openmax < 0) {
virReportSystemError(errno, "%s",
_("sysconf(_SC_OPEN_MAX) failed"));
return EXIT_FAILURE;
}
for (fd = 3; fd < openmax; fd++) {
int tmpfd = fd;
for (i = 3; i < openmax; i++) {
tmpfd = i;
VIR_MASS_CLOSE(tmpfd);
}
/* A fork is required to create new process in correct pid
* namespace. */
if ((ccpid = virFork()) < 0)
if (execv(shargv[0], (char *const*) shargv) < 0) {
virReportSystemError(errno, _("Unable to exec shell %s"),
shargv[0]);
return EXIT_FAILURE;
if (ccpid == 0) {
if (chdir(homedir) < 0) {
virReportSystemError(errno, _("Unable to chdir(%s)"), homedir);
return EXIT_FAILURE;
}
if (execv(shargv[0], (char *const*) shargv) < 0) {
virReportSystemError(errno, _("Unable to exec shell %s"),
shargv[0]);
return EXIT_FAILURE;
}
}
return virProcessWait(ccpid, &status2, true);
return EXIT_SUCCESS;
}
ret = virProcessWait(cpid, &status, true);
if (virProcessWait(cpid, &status, true) < 0)
goto cleanup;
ret = EXIT_SUCCESS;
cleanup:
for (i = 0; i < nfdlist; i++)
VIR_FORCE_CLOSE(fdlist[i]);
VIR_FREE(fdlist);
virConfFree(conf);
virLoginShellFini(conn, dom);
if (dom)
virDomainFree(dom);
if (conn)
virConnectClose(conn);
virStringFreeList(shargv);
VIR_FREE(name);
VIR_FREE(homedir);