[libvirt] [PATCH] qemuDomainSaveMemory: Don't enforce dynamicOwnership

[Michal Privoznik]

https://bugzilla.redhat.com/show_bug.cgi?id=1589115

When doing a memory snapshot qemuOpenFile() is used. This means
that the file where memory is saved is firstly attempted to be
created under root:root (because that's what libvirtd is running
under) and if this fails the second attempt is done under
domain's uid:gid. This does not make much sense - qemu is given
opened FD so it does not need to access the file. Moreover, if
dynamicOwnership is set in qemu.conf and the file lives on a
squashed NFS this is deadly combination and very likely to fail.

The fix consists of using:

  qemuOpenFileAs(fallback_uid = cfg->user,
                 fallback_gid = cfg->group,
                 dynamicOwnership = false)

In other words, dynamicOwnership is turned off for memory
snapshot (chown() will still be attempted if the file does not
live on NFS) and instead of using domain DAC label, configured
user:group is set as fallback.

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/qemu/qemu_driver.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 129bacdd34..6af7e6e171 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -3223,6 +3223,7 @@ qemuDomainSaveMemory(virQEMUDriverPtr driver,
                      unsigned int flags,
                      qemuDomainAsyncJob asyncJob)
 {
+    virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
     bool bypassSecurityDriver = false;
     bool needUnlink = false;
     int ret = -1;
@@ -3241,9 +3242,10 @@ qemuDomainSaveMemory(virQEMUDriverPtr driver,
             goto cleanup;
         }
     }
-    fd = qemuOpenFile(driver, vm, path,
-                      O_WRONLY | O_TRUNC | O_CREAT | directFlag,
-                      &needUnlink, &bypassSecurityDriver);
+
+    fd = qemuOpenFileAs(cfg->user, cfg->group, false, path,
+                        O_WRONLY | O_TRUNC | O_CREAT | directFlag,
+                        &needUnlink, &bypassSecurityDriver);
     if (fd < 0)
         goto cleanup;
 
@@ -3283,6 +3285,7 @@ qemuDomainSaveMemory(virQEMUDriverPtr driver,
  cleanup:
     VIR_FORCE_CLOSE(fd);
     virFileWrapperFdFree(wrapperFd);
+    virObjectUnref(cfg);
 
     if (ret < 0 && needUnlink)
         unlink(path);
-- 
2.16.4