10:38 a.m.
Implement virProcessRunInMountNamespace, which runs callback of type
virProcessNamespaceCallback in a container namespace. This uses a
child process to run the callback, since you can't change the mount
namespace of a thread. This implies that callbacks have to be careful
about what code they run due to async safety rules.
Idea by Dan Berrange, based on an initial report by Reco
<recoverym4n(a)gmail.com> at
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=732394
Signed-off-by: Daniel Berrange <berrange(a)redhat.com>
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
src/libvirt_private.syms | 1 +
src/util/virprocess.c | 107 +++++++++++++++++++++++++++++++++++++++++++++++
src/util/virprocess.h | 11 +++++
3 files changed, 119 insertions(+)
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index f22fe50..eee1df4 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1673,6 +1673,7 @@ virProcessGetNamespaces;
virProcessGetStartTime;
virProcessKill;
virProcessKillPainfully;
+virProcessRunInMountNamespace;
virProcessSetAffinity;
virProcessSetMaxFiles;
virProcessSetMaxMemLock;
diff --git a/src/util/virprocess.c b/src/util/virprocess.c
index 83d0679..5c76674 100644
--- a/src/util/virprocess.c
+++ b/src/util/virprocess.c
@@ -50,6 +50,8 @@
#include "virlog.h"
#include "virutil.h"
#include "virstring.h"
+#include "virthread.h"
+#include "vircommand.h"
#define VIR_FROM_THIS VIR_FROM_NONE
@@ -877,3 +879,108 @@ int virProcessGetStartTime(pid_t pid,
return 0;
}
#endif
+
+
+#ifdef HAVE_SETNS
+static int virProcessNamespaceHelper(int errfd,
+ pid_t pid,
+ virProcessNamespaceCallback cb,
+ void *opaque)
+{
+ char *path;
+ int fd = -1;
+ int ret = -1;
+
+ if (virAsprintf(&path, "/proc/%llu/ns/mnt", (unsigned long long)pid)
< 0)
+ goto cleanup;
+
+ if ((fd = open(path, O_RDONLY)) < 0) {
+ virReportSystemError(errno, "%s",
+ _("Kernel does not provide mount namespace"));
+ goto cleanup;
+ }
+
+ if (setns(fd, 0) < 0) {
+ virReportSystemError(errno, "%s",
+ _("Unable to enter mount namespace"));
+ goto cleanup;
+ }
+
+ ret = cb(pid, opaque);
+
+ cleanup:
+ if (ret < 0) {
+ virErrorPtr err = virGetLastError();
+ if (err) {
+ size_t len = strlen(err->message) + 1;
+ ignore_value(safewrite(errfd, err->message, len));
+ }
+ }
+ VIR_FREE(path);
+ VIR_FORCE_CLOSE(fd);
+ return ret;
+}
+
+/* Run cb(opaque) in the mount namespace of pid. Return -1 with error
+ * message raised if we fail to run the child, if the child dies from
+ * a signal, or if the child has status 1; otherwise return the exit
+ * status of the child. The callback will be run in a child process
+ * so must be careful to only use async signal safe functions.
+ */
+int
+virProcessRunInMountNamespace(pid_t pid,
+ virProcessNamespaceCallback cb,
+ void *opaque)
+{
+ int ret = -1;
+ pid_t child = -1;
+ int errfd[2] = { -1, -1 };
+
+ if (pipe(errfd) < 0) {
+ virReportSystemError(errno, "%s",
+ _("Cannot create pipe for child"));
+ return -1;
+ }
+
+ ret = virFork(&child);
+
+ if (ret < 0 || child < 0) {
+ if (child == 0)
+ _exit(1);
+
+ /* parent */
+ virProcessAbort(child);
+ goto cleanup;
+ }
+
+ if (child == 0) {
+ VIR_FORCE_CLOSE(errfd[0]);
+ ret = virProcessNamespaceHelper(errfd[1], pid,
+ cb, opaque);
+ VIR_FORCE_CLOSE(errfd[1]);
+ _exit(ret < 0 ? 1 : 0);
+ } else {
+ char *buf = NULL;
+ VIR_FORCE_CLOSE(errfd[1]);
+
+ ignore_value(virFileReadHeaderFD(errfd[0], 1024, &buf));
+ ret = virProcessWait(child, NULL);
+ VIR_FREE(buf);
+ }
+
+cleanup:
+ VIR_FORCE_CLOSE(errfd[0]);
+ VIR_FORCE_CLOSE(errfd[1]);
+ return ret;
+}
+#else /* !HAVE_SETNS */
+int
+virProcessRunInMountNamespace(pid_t pid ATTRIBUTE_UNUSED,
+ virProcessNamespaceCallback cb ATTRIBUTE_UNUSED,
+ void *opaque ATTRIBUTE_UNUSED)
+{
+ virReportSystemError(ENOSYS, "%s",
+ _("Mount namespaces are not available on this
platform"));
+ return -1;
+}
+#endif
diff --git a/src/util/virprocess.h b/src/util/virprocess.h
index 9f77bc5..5c173b0 100644
--- a/src/util/virprocess.h
+++ b/src/util/virprocess.h
@@ -60,4 +60,15 @@ int virProcessSetNamespaces(size_t nfdlist,
int virProcessSetMaxMemLock(pid_t pid, unsigned long long bytes);
int virProcessSetMaxProcesses(pid_t pid, unsigned int procs);
int virProcessSetMaxFiles(pid_t pid, unsigned int files);
+
+/* Callback to run code within the mount namespace tied to the given
+ * pid. This function must use only async-signal-safe functions, as
+ * it gets run after a fork of a multi-threaded process. The return
+ * value of this function is passed to _exit(), except that a
+ * negative value is treated as an error. */
+typedef int (*virProcessNamespaceCallback)(pid_t pid, void *opaque);
+
+int virProcessRunInMountNamespace(pid_t pid,
+ virProcessNamespaceCallback cb,
+ void *opaque);
#endif /* __VIR_PROCESS_H__ */
--
1.8.5.3