From d9369eae049c780ebd130a13eedfaaf3586242eb Mon Sep 17 00:00:00 2001

Message-Id: <d9369eae049c780ebd130a13eedfaaf3586242eb@dist-git>

From: Michal Privoznik <mprivozn@redhat.com>

Date: Mon, 9 Mar 2020 14:58:57 +0100

Subject: [PATCH] qemu: Tell secdrivers which images are top parent

When preparing images for block jobs we modify their seclabels so

that QEMU can open them. However, as mentioned in the previous

commit, secdrivers base some it their decisions whether the image

they are working on is top of of the backing chain. Fortunately,

in places where we call secdrivers we know this and the

information can be passed to secdrivers.

The problem is the following: after the first blockcommit from

the base to one of the parents the XATTRs on the base image are

not cleared and therefore the second attempt to do another

blockcommit fails. This is caused by blockcommit code calling

qemuSecuritySetImageLabel() over the base image, possibly

multiple times (to ensure RW/RO access). A naive fix would be to

call the restore function. But this is not possible, because that

would deny QEMU the access to the base image.  Fortunately, we

can use the fact that seclabels are remembered only for the top

of the backing chain and not for the rest of the backing chain.

And thanks to the previous commit we can tell secdrivers which

images are top of the backing chain.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1803551

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

Reviewed-by: Peter Krempa <pkrempa@redhat.com>

(cherry picked from commit 13eb6c14682004d0dc692554475125db0f161da7)

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

Message-Id: <a8d9171d9f88b325480c17969e074d62d3eeba3b.1583760062.git.mprivozn@redhat.com>

Reviewed-by: Jiri Denemark <jdenemar@redhat.com>

---

 src/qemu/qemu_backup.c     |  4 ++--

 src/qemu/qemu_blockjob.c   |  6 ++++--

 src/qemu/qemu_checkpoint.c |  6 ++++--

 src/qemu/qemu_domain.c     | 24 ++++++++++++++++++++----

 src/qemu/qemu_domain.h     |  3 ++-

 src/qemu/qemu_driver.c     | 23 +++++++++++++++++------

 src/qemu/qemu_process.c    |  2 +-

 src/qemu/qemu_security.c   |  6 +++++-

 src/qemu/qemu_security.h   |  3 ++-

 9 files changed, 57 insertions(+), 20 deletions(-)

diff --git a/src/qemu/qemu_backup.c b/src/qemu/qemu_backup.c

index 2cc6ff7a42..8b66ee8d1f 100644

--- a/src/qemu/qemu_backup.c

+++ b/src/qemu/qemu_backup.c

@@ -469,8 +469,8 @@ qemuBackupDiskPrepareOneStorage(virDomainObjPtr vm,

         dd->created = true;

     }

-    if (qemuDomainStorageSourceAccessAllow(priv->driver, vm, dd->store, false,

-                                           true) < 0)

+    if (qemuDomainStorageSourceAccessAllow(priv->driver, vm, dd->store,

+                                           false, true, true) < 0)

         return -1;

     dd->labelled = true;

diff --git a/src/qemu/qemu_blockjob.c b/src/qemu/qemu_blockjob.c

index 71df0d1ab2..e894e1634d 100644

--- a/src/qemu/qemu_blockjob.c

+++ b/src/qemu/qemu_blockjob.c

@@ -1105,9 +1105,11 @@ qemuBlockJobProcessEventCompletedCommit(virQEMUDriverPtr driver,

         return;

     /* revert access to images */

-    qemuDomainStorageSourceAccessAllow(driver, vm, job->data.commit.base, true, false);

+    qemuDomainStorageSourceAccessAllow(driver, vm, job->data.commit.base,

+                                       true, false, false);

     if (job->data.commit.topparent != job->disk->src)

-        qemuDomainStorageSourceAccessAllow(driver, vm, job->data.commit.topparent, true, false);

+        qemuDomainStorageSourceAccessAllow(driver, vm, job->data.commit.topparent,

+                                           true, false, true);

     baseparent->backingStore = NULL;

     job->data.commit.topparent->backingStore = job->data.commit.base;

diff --git a/src/qemu/qemu_checkpoint.c b/src/qemu/qemu_checkpoint.c

index c06bfe6a21..fe54af74ec 100644

--- a/src/qemu/qemu_checkpoint.c

+++ b/src/qemu/qemu_checkpoint.c

@@ -298,7 +298,8 @@ qemuCheckpointDiscardBitmaps(virDomainObjPtr vm,

     for (next = reopenimages; next; next = next->next) {

         virStorageSourcePtr src = next->data;

-        if (qemuDomainStorageSourceAccessAllow(driver, vm, src, false, false) < 0)

+        if (qemuDomainStorageSourceAccessAllow(driver, vm, src,

+                                               false, false, false) < 0)

             goto relabel;

         relabelimages = g_slist_prepend(relabelimages, src);

@@ -313,7 +314,8 @@ qemuCheckpointDiscardBitmaps(virDomainObjPtr vm,

     for (next = relabelimages; next; next = next->next) {

         virStorageSourcePtr src = next->data;

-        ignore_value(qemuDomainStorageSourceAccessAllow(driver, vm, src, true, false));

+        ignore_value(qemuDomainStorageSourceAccessAllow(driver, vm, src,

+                                                        true, false, false));

     }

     return rc;

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c

index 3cbe7ef6e1..14bab896bc 100644

--- a/src/qemu/qemu_domain.c

+++ b/src/qemu/qemu_domain.c

@@ -11770,6 +11770,8 @@ typedef enum {

     QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_SKIP_REVOKE = 1 << 4,

     /* VM already has access to the source and we are just modifying it */

     QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_MODIFY_ACCESS = 1 << 5,

+    /* whether the image is the top image of the backing chain (e.g. disk source) */

+    QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_CHAIN_TOP = 1 << 6,

 } qemuDomainStorageSourceAccessFlags;

@@ -11847,6 +11849,7 @@ qemuDomainStorageSourceAccessModify(virQEMUDriverPtr driver,

     bool force_ro = flags & QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_FORCE_READ_ONLY;

     bool force_rw = flags & QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_FORCE_READ_WRITE;

     bool revoke = flags & QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_REVOKE;

+    bool chain_top = flags & QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_CHAIN_TOP;

     int rc;

     bool was_readonly = src->readonly;

     bool revoke_cgroup = false;

@@ -11893,7 +11896,7 @@ qemuDomainStorageSourceAccessModify(virQEMUDriverPtr driver,

         revoke_namespace = true;

     }

-    if (qemuSecuritySetImageLabel(driver, vm, src, chain) < 0)

+    if (qemuSecuritySetImageLabel(driver, vm, src, chain, chain_top) < 0)

         goto revoke;

     revoke_label = true;

@@ -11956,7 +11959,8 @@ qemuDomainStorageSourceChainAccessAllow(virQEMUDriverPtr driver,

                                         virDomainObjPtr vm,

                                         virStorageSourcePtr src)

 {

-    qemuDomainStorageSourceAccessFlags flags = QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_CHAIN;

+    qemuDomainStorageSourceAccessFlags flags = QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_CHAIN |

+                                               QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_CHAIN_TOP;

     return qemuDomainStorageSourceAccessModify(driver, vm, src, flags);

 }

@@ -11968,7 +11972,8 @@ qemuDomainStorageSourceChainAccessRevoke(virQEMUDriverPtr driver,

                                          virStorageSourcePtr src)

 {

     qemuDomainStorageSourceAccessFlags flags = QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_REVOKE |

-                                               QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_CHAIN;

+                                               QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_CHAIN |

+                                               QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_CHAIN_TOP;

     return qemuDomainStorageSourceAccessModify(driver, vm, src, flags);

 }

@@ -11998,6 +12003,7 @@ qemuDomainStorageSourceAccessRevoke(virQEMUDriverPtr driver,

  * @elem: source structure to set access for

  * @readonly: setup read-only access if true

  * @newSource: @elem describes a storage source which @vm can't access yet

+ * @chainTop: @elem is top parent of backing chain

  *

  * Allow a VM access to a single element of a disk backing chain; this helper

  * ensures that the lock manager, cgroup device controller, and security manager

@@ -12005,13 +12011,20 @@ qemuDomainStorageSourceAccessRevoke(virQEMUDriverPtr driver,

  *

  * When modifying permissions of @elem which @vm can already access (is in the

  * backing chain) @newSource needs to be set to false.

+ *

+ * The @chainTop flag must be set if the @elem image is the topmost image of a

+ * given backing chain or meant to become the topmost image (for e.g.

+ * snapshots, or blockcopy or even in the end for active layer block commit,

+ * where we discard the top of the backing chain so one of the intermediates

+ * (the base) becomes the top of the chain).

  */

 int

 qemuDomainStorageSourceAccessAllow(virQEMUDriverPtr driver,

                                    virDomainObjPtr vm,

                                    virStorageSourcePtr elem,

                                    bool readonly,

-                                   bool newSource)

+                                   bool newSource,

+                                   bool chainTop)

 {

     qemuDomainStorageSourceAccessFlags flags = QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_SKIP_REVOKE;

@@ -12023,6 +12036,9 @@ qemuDomainStorageSourceAccessAllow(virQEMUDriverPtr driver,

     if (!newSource)

         flags |= QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_MODIFY_ACCESS;

+    if (chainTop)

+        flags |= QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_CHAIN_TOP;

+

     return qemuDomainStorageSourceAccessModify(driver, vm, elem, flags);

 }

diff --git a/src/qemu/qemu_domain.h b/src/qemu/qemu_domain.h

index 83150e4e6d..9d143b575d 100644

--- a/src/qemu/qemu_domain.h

+++ b/src/qemu/qemu_domain.h

@@ -895,7 +895,8 @@ int qemuDomainStorageSourceAccessAllow(virQEMUDriverPtr driver,

                                        virDomainObjPtr vm,

                                        virStorageSourcePtr elem,

                                        bool readonly,

-                                       bool newSource);

+                                       bool newSource,

+                                       bool chainTop);

 int qemuDomainPrepareStorageSourceBlockdev(virDomainDiskDefPtr disk,

                                            virStorageSourcePtr src,

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c

index d346446444..26f100177b 100644

--- a/src/qemu/qemu_driver.c

+++ b/src/qemu/qemu_driver.c

@@ -15467,7 +15467,8 @@ qemuDomainSnapshotDiskPrepareOne(virQEMUDriverPtr driver,

     }

     /* set correct security, cgroup and locking options on the new image */

-    if (qemuDomainStorageSourceAccessAllow(driver, vm, dd->src, false, true) < 0)

+    if (qemuDomainStorageSourceAccessAllow(driver, vm, dd->src,

+                                           false, true, true) < 0)

         return -1;

     dd->prepared = true;

@@ -18815,11 +18816,19 @@ qemuDomainBlockCommit(virDomainPtr dom,

      * operation succeeds, but doing that requires tracking the

      * operation in XML across libvirtd restarts.  */

     clean_access = true;

-    if (qemuDomainStorageSourceAccessAllow(driver, vm, baseSource, false, false) < 0 ||

-        (top_parent && top_parent != disk->src &&

-         qemuDomainStorageSourceAccessAllow(driver, vm, top_parent, false, false) < 0))

+    if (qemuDomainStorageSourceAccessAllow(driver, vm, baseSource,

+                                           false, false, false) < 0)

         goto endjob;

+    if (top_parent && top_parent != disk->src) {

+        /* While top_parent is topmost image, we don't need to remember its

+         * owner as it will be overwritten upon finishing the commit. Hence,

+         * pass chainTop = false. */

+        if (qemuDomainStorageSourceAccessAllow(driver, vm, top_parent,

+                                               false, false, false) < 0)

+            goto endjob;

+    }

+

     if (!(job = qemuBlockJobDiskNewCommit(vm, disk, top_parent, topSource,

                                           baseSource,

                                           flags & VIR_DOMAIN_BLOCK_COMMIT_DELETE,

@@ -18877,9 +18886,11 @@ qemuDomainBlockCommit(virDomainPtr dom,

         virErrorPtr orig_err;

         virErrorPreserveLast(&orig_err);

         /* Revert access to read-only, if possible.  */

-        qemuDomainStorageSourceAccessAllow(driver, vm, baseSource, true, false);

+        qemuDomainStorageSourceAccessAllow(driver, vm, baseSource,

+                                           true, false, false);

         if (top_parent && top_parent != disk->src)

-            qemuDomainStorageSourceAccessAllow(driver, vm, top_parent, true, false);

+            qemuDomainStorageSourceAccessAllow(driver, vm, top_parent,

+                                               true, false, false);

         virErrorRestore(&orig_err);

     }

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c

index 0476f18517..dffff04554 100644

--- a/src/qemu/qemu_process.c

+++ b/src/qemu/qemu_process.c

@@ -7823,7 +7823,7 @@ qemuProcessRefreshLegacyBlockjob(void *payload,

                 (qemuDomainNamespaceSetupDisk(vm, disk->mirror) < 0 ||

                  qemuSetupImageChainCgroup(vm, disk->mirror) < 0 ||

                  qemuSecuritySetImageLabel(priv->driver, vm, disk->mirror,

-                                           true) < 0))

+                                           true, true) < 0))

                 goto cleanup;

         }

     }

diff --git a/src/qemu/qemu_security.c b/src/qemu/qemu_security.c

index 2aa2b5b9c6..484fc34552 100644

--- a/src/qemu/qemu_security.c

+++ b/src/qemu/qemu_security.c

@@ -98,7 +98,8 @@ int

 qemuSecuritySetImageLabel(virQEMUDriverPtr driver,

                           virDomainObjPtr vm,

                           virStorageSourcePtr src,

-                          bool backingChain)

+                          bool backingChain,

+                          bool chainTop)

 {

     qemuDomainObjPrivatePtr priv = vm->privateData;

     pid_t pid = -1;

@@ -108,6 +109,9 @@ qemuSecuritySetImageLabel(virQEMUDriverPtr driver,

     if (backingChain)

         labelFlags |= VIR_SECURITY_DOMAIN_IMAGE_LABEL_BACKING_CHAIN;

+    if (chainTop)

+        labelFlags |= VIR_SECURITY_DOMAIN_IMAGE_PARENT_CHAIN_TOP;

+

     if (qemuDomainNamespaceEnabled(vm, QEMU_DOMAIN_NS_MOUNT))

         pid = vm->pid;

diff --git a/src/qemu/qemu_security.h b/src/qemu/qemu_security.h

index a8c648ece1..c8516005ac 100644

--- a/src/qemu/qemu_security.h

+++ b/src/qemu/qemu_security.h

@@ -36,7 +36,8 @@ void qemuSecurityRestoreAllLabel(virQEMUDriverPtr driver,

 int qemuSecuritySetImageLabel(virQEMUDriverPtr driver,

                               virDomainObjPtr vm,

                               virStorageSourcePtr src,

-                              bool backingChain);

+                              bool backingChain,

+                              bool chainTop);

 int qemuSecurityRestoreImageLabel(virQEMUDriverPtr driver,

                                   virDomainObjPtr vm,

-- 

2.25.1