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snapshot: Avoid latent use-after-free when cleaning snapshots
Right now, the only callers of qemuDomainSnapshotDiscardAllMetadata() are right before freeing the virDomainSnapshotObjList, so it did not matter if the list's metaroot (which points to all the defined root snapshots) is left inconsistent. But an upcoming patch will want to clear all snapshots if a bulk redefine fails partway through, in which case things must be reset. Make this work by teaching the existing virDomainSnapshotUpdateRelations() to be safe regardless of the incoming state of the metaroot (since we don't want to leak that internal detail into qemu code), then fixing the qemu code to use it after deleting all snapshots. Additionally, the qemu code must reset vm->current_snapshot if the current snapshot was removed, regardless of whether the overall removal succeeded or failed later. Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: John Ferlan <jferlan@redhat.com>
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@ -1206,13 +1206,16 @@ virDomainSnapshotSetRelations(void *payload,
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}
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/* Populate parent link and child count of all snapshots, with all
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* relations starting as 0/NULL. Return 0 on success, -1 if a parent
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* is missing or if a circular relationship was requested. */
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* assigned defs having relations starting as 0/NULL. Return 0 on
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* success, -1 if a parent is missing or if a circular relationship
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* was requested. */
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int
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virDomainSnapshotUpdateRelations(virDomainSnapshotObjListPtr snapshots)
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{
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struct snapshot_set_relation act = { snapshots, 0 };
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snapshots->metaroot.nchildren = 0;
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snapshots->metaroot.first_child = NULL;
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virHashForEach(snapshots->objs, virDomainSnapshotSetRelations, &act);
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return act.err;
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}
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@ -8625,6 +8625,10 @@ qemuDomainSnapshotDiscardAllMetadata(virQEMUDriverPtr driver,
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rem.err = 0;
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virDomainSnapshotForEach(vm->snapshots, qemuDomainSnapshotDiscardAll,
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&rem);
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if (rem.current)
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vm->current_snapshot = NULL;
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if (virDomainSnapshotUpdateRelations(vm->snapshots) < 0 && !rem.err)
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rem.err = -1;
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return rem.err;
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}
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