[libvirt] [PATCH sandbox] Ensure libvirt-sandbox-init-common uses correct ld-linux

[Daniel P. Berrange]

The libc.so library requires certainly functionality to be
provided by the ld-linux.so library. The ld-linux.so is loaded
by the kernel based on the PT_INTERP ELF section, and as such
LD_LIBRARY_PATH has no effect.

So, although libvirt-sandbox-init-{qemu,lxc} set LD_LIBRARY_PATH
to force use of the libs from the host OS image, the common
init program was stil using the ld-linux.so from the guest OS
image. Sometimes this works, sometimes it breaks.

When trying to run Fedora 19 as the root filesystem from a
Fedora 22 host, it would break thus:

/etc/libvirt-sandbox/scratch/.libs/libvirt-sandbox-init-common: relocation error: /etc/libvirt-sandbox/scratch/.libs/libc.so.6: symbol _dl_find_dso_for_object, version GLIBC_PRIVATE not defined in file ld-linux-x86-64.so.2 with link time reference

To deal with this we must ensure that we always invoke the
libvirt-sandbox-init-common program using the ld-linux that
was provided by the host OS image.

The sandbox builder is tweaked so that it always copies the
host ld-linux.so into the libs scratch directory, and gives
it a predictable name 'ld.so', since every architecture seems
to have a different name.

The libvirt-sandbox-init-{lxc,qemu} files are changed so that
instead of exec'ing libvirt-sandbox-init-common directly, they
will load it via the ld.so file.
---
 libvirt-sandbox/libvirt-sandbox-builder.c   | 28 +++++++++++++++++++++++-----
 libvirt-sandbox/libvirt-sandbox-init-lxc.c  |  1 +
 libvirt-sandbox/libvirt-sandbox-init-qemu.c |  1 +
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/libvirt-sandbox/libvirt-sandbox-builder.c b/libvirt-sandbox/libvirt-sandbox-builder.c
index 2726868..e615606 100644
--- a/libvirt-sandbox/libvirt-sandbox-builder.c
+++ b/libvirt-sandbox/libvirt-sandbox-builder.c
@@ -252,10 +252,11 @@ GVirConnection *gvir_sandbox_builder_get_connection(GVirSandboxBuilder *builder)
 
 static gboolean gvir_sandbox_builder_copy_file(const char *path,
                                                const char *libsdir,
+                                               const char *newname,
                                                GError **error)
 {
     gchar *name = g_path_get_basename(path);
-    gchar *target = g_build_filename(libsdir, name, NULL);
+    gchar *target = g_build_filename(libsdir, newname ? newname : name, NULL);
     GFile *srcFile = g_file_new_for_path(path);
     GFile *tgtFile = g_file_new_for_path(target);
     gboolean result = FALSE;
@@ -285,7 +286,7 @@ static gboolean gvir_sandbox_builder_copy_program(const char *program,
     const gchar *argv[] = {LDD_PATH, program, NULL};
     gboolean result = FALSE;
 
-    if (!gvir_sandbox_builder_copy_file(program, dest, error))
+    if (!gvir_sandbox_builder_copy_file(program, dest, NULL, error))
         goto cleanup;
 
 
@@ -301,14 +302,31 @@ static gboolean gvir_sandbox_builder_copy_program(const char *program,
         *tmp = '\0';
 
         /* Search the line for the library path */
-        start = strstr(line, " => ");
+        start = strstr(line, "/");
         end = strstr(line, " (");
 
         if (start && end) {
-            start = start + 4;
+            const gchar *newname = NULL;
             *end = '\0';
 
-            if (!gvir_sandbox_builder_copy_file(start, dest, error))
+            /* There are countless different naming schemes for
+             * the ld-linux.so library across architectures. Pretty
+             * much the only thing in common is they start with
+             * the two letters 'ld'. The LDD program prints it
+             * out differently too - it doesn't include " => "
+             * as this library is special - its actually a static
+             * linked executable not a library.
+             *
+             * To make life easier for libvirt-sandbox-init-{qemu,lxc}
+             * we just call the file 'ld.so' when we copy it into our
+             * scratch dir, no matter what it was called on the host.
+             */
+            if (!strstr(line, " => ") &&
+                strstr(start, "/ld")) {
+                newname = "ld.so";
+            }
+
+            if (!gvir_sandbox_builder_copy_file(start, dest, newname, error))
                 goto cleanup;
         }
 
diff --git a/libvirt-sandbox/libvirt-sandbox-init-lxc.c b/libvirt-sandbox/libvirt-sandbox-init-lxc.c
index e2fe7f0..d1e4a79 100644
--- a/libvirt-sandbox/libvirt-sandbox-init-lxc.c
+++ b/libvirt-sandbox/libvirt-sandbox-init-lxc.c
@@ -77,6 +77,7 @@ main(int argc, char **argv)
         args[narg++] = "1000";
     }
 
+    args[narg++] = SANDBOXCONFIGDIR "/.libs/ld.so";
     args[narg++] = SANDBOXCONFIGDIR "/.libs/libvirt-sandbox-init-common";
     if (debug)
         args[narg++] = "-d";
diff --git a/libvirt-sandbox/libvirt-sandbox-init-qemu.c b/libvirt-sandbox/libvirt-sandbox-init-qemu.c
index 09580da..cd6055a 100644
--- a/libvirt-sandbox/libvirt-sandbox-init-qemu.c
+++ b/libvirt-sandbox/libvirt-sandbox-init-qemu.c
@@ -422,6 +422,7 @@ main(int argc ATTR_UNUSED, char **argv ATTR_UNUSED)
         args[narg++] = "1000";
     }
 
+    args[narg++] = SANDBOXCONFIGDIR "/.libs/ld.so";
     args[narg++] = SANDBOXCONFIGDIR "/.libs/libvirt-sandbox-init-common";
     if (debug)
         args[narg++] = "-d";
-- 
2.4.3