xen/663eaa27-libxl-XenStore-error-handling-in-device-creation.patch

# Commit 531d3bea5e9357357eaf6d40f5784a1b4c29b910
# Date 2024-05-11 00:13:43 +0100
# Author Demi Marie Obenour <demi@invisiblethingslab.com>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
libxl: Fix handling XenStore errors in device creation

If xenstored runs out of memory it is possible for it to fail operations
that should succeed.  libxl wasn't robust against this, and could fail
to ensure that the TTY path of a non-initial console was created and
read-only for guests.  This doesn't qualify for an XSA because guests
should not be able to run xenstored out of memory, but it still needs to
be fixed.

Add the missing error checks to ensure that all errors are properly
handled and that at no point can a guest make the TTY path of its
frontend directory writable.

Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Reviewed-by: Juergen Gross <jgross@suse.com>

--- a/tools/libs/light/libxl_console.c
+++ b/tools/libs/light/libxl_console.c
@@ -351,11 +351,10 @@ int libxl__device_console_add(libxl__gc
         flexarray_append(front, "protocol");
         flexarray_append(front, LIBXL_XENCONSOLE_PROTOCOL);
     }
-    libxl__device_generic_add(gc, XBT_NULL, device,
-                              libxl__xs_kvs_of_flexarray(gc, back),
-                              libxl__xs_kvs_of_flexarray(gc, front),
-                              libxl__xs_kvs_of_flexarray(gc, ro_front));
-    rc = 0;
+    rc = libxl__device_generic_add(gc, XBT_NULL, device,
+                                   libxl__xs_kvs_of_flexarray(gc, back),
+                                   libxl__xs_kvs_of_flexarray(gc, front),
+                                   libxl__xs_kvs_of_flexarray(gc, ro_front));
 out:
     return rc;
 }
@@ -665,6 +664,8 @@ int libxl_device_channel_getinfo(libxl_c
               */
              if (!val) val = "/NO-SUCH-PATH";
              channelinfo->u.pty.path = strdup(val);
+             if (channelinfo->u.pty.path == NULL)
+                 abort();
              break;
          default:
              break;
--- a/tools/libs/light/libxl_device.c
+++ b/tools/libs/light/libxl_device.c
@@ -177,8 +177,13 @@ int libxl__device_generic_add(libxl__gc
     ro_frontend_perms[1].perms = backend_perms[1].perms = XS_PERM_READ;
 
 retry_transaction:
-    if (create_transaction)
+    if (create_transaction) {
         t = xs_transaction_start(ctx->xsh);
+        if (t == XBT_NULL) {
+            LOGED(ERROR, device->domid, "xs_transaction_start failed");
+            return ERROR_FAIL;
+        }
+    }
 
     /* FIXME: read frontend_path and check state before removing stuff */
 
@@ -195,42 +200,55 @@ retry_transaction:
         if (rc) goto out;
     }
 
-    /* xxx much of this function lacks error checks! */
-
     if (fents || ro_fents) {
-        xs_rm(ctx->xsh, t, frontend_path);
-        xs_mkdir(ctx->xsh, t, frontend_path);
+        if (!xs_rm(ctx->xsh, t, frontend_path) && errno != ENOENT)
+            goto out;
+        if (!xs_mkdir(ctx->xsh, t, frontend_path))
+            goto out;
         /* Console 0 is a special case. It doesn't use the regular PV
          * state machine but also the frontend directory has
          * historically contained other information, such as the
          * vnc-port, which we don't want the guest fiddling with.
          */
         if ((device->kind == LIBXL__DEVICE_KIND_CONSOLE && device->devid == 0) ||
-            (device->kind == LIBXL__DEVICE_KIND_VUART))
-            xs_set_permissions(ctx->xsh, t, frontend_path,
-                               ro_frontend_perms, ARRAY_SIZE(ro_frontend_perms));
-        else
-            xs_set_permissions(ctx->xsh, t, frontend_path,
-                               frontend_perms, ARRAY_SIZE(frontend_perms));
-        xs_write(ctx->xsh, t, GCSPRINTF("%s/backend", frontend_path),
-                 backend_path, strlen(backend_path));
-        if (fents)
-            libxl__xs_writev_perms(gc, t, frontend_path, fents,
-                                   frontend_perms, ARRAY_SIZE(frontend_perms));
-        if (ro_fents)
-            libxl__xs_writev_perms(gc, t, frontend_path, ro_fents,
-                                   ro_frontend_perms, ARRAY_SIZE(ro_frontend_perms));
+            (device->kind == LIBXL__DEVICE_KIND_VUART)) {
+            if (!xs_set_permissions(ctx->xsh, t, frontend_path,
+                                    ro_frontend_perms, ARRAY_SIZE(ro_frontend_perms)))
+                goto out;
+        } else {
+            if (!xs_set_permissions(ctx->xsh, t, frontend_path,
+                                    frontend_perms, ARRAY_SIZE(frontend_perms)))
+                goto out;
+        }
+        if (!xs_write(ctx->xsh, t, GCSPRINTF("%s/backend", frontend_path),
+                      backend_path, strlen(backend_path)))
+            goto out;
+        if (fents) {
+            rc = libxl__xs_writev_perms(gc, t, frontend_path, fents,
+                                        frontend_perms, ARRAY_SIZE(frontend_perms));
+            if (rc) goto out;
+        }
+        if (ro_fents) {
+            rc = libxl__xs_writev_perms(gc, t, frontend_path, ro_fents,
+                                        ro_frontend_perms, ARRAY_SIZE(ro_frontend_perms));
+            if (rc) goto out;
+        }
     }
 
     if (bents) {
         if (!libxl_only) {
-            xs_rm(ctx->xsh, t, backend_path);
-            xs_mkdir(ctx->xsh, t, backend_path);
-            xs_set_permissions(ctx->xsh, t, backend_path, backend_perms,
-                               ARRAY_SIZE(backend_perms));
-            xs_write(ctx->xsh, t, GCSPRINTF("%s/frontend", backend_path),
-                     frontend_path, strlen(frontend_path));
-            libxl__xs_writev(gc, t, backend_path, bents);
+            if (!xs_rm(ctx->xsh, t, backend_path) && errno != ENOENT)
+                goto out;
+            if (!xs_mkdir(ctx->xsh, t, backend_path))
+                goto out;
+            if (!xs_set_permissions(ctx->xsh, t, backend_path, backend_perms,
+                                    ARRAY_SIZE(backend_perms)))
+                goto out;
+            if (!xs_write(ctx->xsh, t, GCSPRINTF("%s/frontend", backend_path),
+                          frontend_path, strlen(frontend_path)))
+                goto out;
+            rc = libxl__xs_writev(gc, t, backend_path, bents);
+            if (rc) goto out;
         }
 
         /*
@@ -276,7 +294,7 @@ retry_transaction:
  out:
     if (create_transaction && t)
         libxl__xs_transaction_abort(gc, &t);
-    return rc;
+    return rc != 0 ? rc : ERROR_FAIL;
 }
 
 typedef struct {
--- a/tools/libs/light/libxl_xshelp.c
+++ b/tools/libs/light/libxl_xshelp.c
@@ -60,10 +60,15 @@ int libxl__xs_writev_perms(libxl__gc *gc
     for (i = 0; kvs[i] != NULL; i += 2) {
         path = GCSPRINTF("%s/%s", dir, kvs[i]);
         if (path && kvs[i + 1]) {
-            int length = strlen(kvs[i + 1]);
-            xs_write(ctx->xsh, t, path, kvs[i + 1], length);
-            if (perms)
-                xs_set_permissions(ctx->xsh, t, path, perms, num_perms);
+            size_t length = strlen(kvs[i + 1]);
+            if (length > UINT_MAX)
+                return ERROR_FAIL;
+            if (!xs_write(ctx->xsh, t, path, kvs[i + 1], length))
+                return ERROR_FAIL;
+            if (perms) {
+                if (!xs_set_permissions(ctx->xsh, t, path, perms, num_perms))
+                    return ERROR_FAIL;
+            }
         }
     }
     return 0;