[libvirt] [PATCH v2] 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>
---

Diff to v1:
- Fix doCoreDump too (raised in review by John).

 src/qemu/qemu_driver.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 9a35e04a85..86674e519b 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -3185,6 +3185,7 @@ qemuDomainSaveMemory(virQEMUDriverPtr driver,
                      unsigned int flags,
                      qemuDomainAsyncJob asyncJob)
 {
+    virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
     bool needUnlink = false;
     int ret = -1;
     int fd = -1;
@@ -3202,9 +3203,10 @@ qemuDomainSaveMemory(virQEMUDriverPtr driver,
             goto cleanup;
         }
     }
-    fd = qemuOpenFile(driver, vm, path,
-                      O_WRONLY | O_TRUNC | O_CREAT | directFlag,
-                      &needUnlink);
+
+    fd = qemuOpenFileAs(cfg->user, cfg->group, false, path,
+                        O_WRONLY | O_TRUNC | O_CREAT | directFlag,
+                        &needUnlink);
     if (fd < 0)
         goto cleanup;
 
@@ -3244,6 +3246,7 @@ qemuDomainSaveMemory(virQEMUDriverPtr driver,
  cleanup:
     VIR_FORCE_CLOSE(fd);
     virFileWrapperFdFree(wrapperFd);
+    virObjectUnref(cfg);
 
     if (ret < 0 && needUnlink)
         unlink(path);
@@ -3793,9 +3796,9 @@ doCoreDump(virQEMUDriverPtr driver,
     /* Core dumps usually imply last-ditch analysis efforts are
      * desired, so we intentionally do not unlink even if a file was
      * created.  */
-    if ((fd = qemuOpenFile(driver, vm, path,
-                           O_CREAT | O_TRUNC | O_WRONLY | directFlag,
-                           NULL)) < 0)
+    if ((fd = qemuOpenFileAs(cfg->user, cfg->group, false, path,
+                             O_CREAT | O_TRUNC | O_WRONLY | directFlag,
+                             NULL)) < 0)
         goto cleanup;
 
     if (!(wrapperFd = virFileWrapperFdNew(&fd, path, flags)))
-- 
2.16.4