[Qemu-devel] [PATCH for-2.9 0/2] block/mirror: Fix use-after-free

[Qemu-devel] [PATCH for-2.9 0/2] block/mirror: Fix use-after-free

[Max Reitz]

And the exciting 2.9 ride continues!

When mirroring from a BDS with no parents at all (such as those added
with -blockdev or blockdev-add), we have a use-after-free in mirror's
error path. The first patch of this series fixes that, the other adds a
patch so we don't regress.

What issue will we find next? Stay tuned!


Max Reitz (2):
  block/mirror: Fix use-after-free
  iotests: Add mirror tests for orphaned source

 block/mirror.c                | 12 +++++++++--
 tests/qemu-iotests/041        | 46 +++++++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/041.out    |  4 ++--
 tests/qemu-iotests/iotests.py | 15 ++++++++++++++
 4 files changed, 73 insertions(+), 4 deletions(-)

-- 
2.12.1

[Qemu-devel] [PATCH for-2.9 1/2] block/mirror: Fix use-after-free

[Max Reitz]

If @bs does not have any parents, the only reference to @mirror_top_bs
will be held by the BlockJob object after the bdrv_unref() following
block_job_create(). However, if block_job_create() fails, this reference
will not exist and @mirror_top_bs will have been deleted when we
goto fail.

The issue comes back at all later entries to the fail label: We delete
the BlockJob object before rolling back our changes to the node graph.
This means that we will delete @mirror_top_bs in the process.

All in all, whenever @bs does not have any parents and we go down the
fail path we will dereference @mirror_top_bs after it has been deleted.

Fix this by invoking bdrv_unref() only when block_job_create() was
successful and by bdrv_ref()'ing @mirror_top_bs in the fail path before
deleting the BlockJob object. Finally, bdrv_unref() it at the end of the
fail path after we actually no longer need it.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/mirror.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/block/mirror.c b/block/mirror.c
index 9e2fecc15e..46ecd38ef0 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1150,7 +1150,7 @@ static void mirror_start_job(const char *job_id, BlockDriverState *bs,
     mirror_top_bs->total_sectors = bs->total_sectors;
 
     /* bdrv_append takes ownership of the mirror_top_bs reference, need to keep
-     * it alive until block_job_create() even if bs has no parent. */
+     * it alive until block_job_create() succeeds even if bs has no parent. */
     bdrv_ref(mirror_top_bs);
     bdrv_drained_begin(bs);
     bdrv_append(mirror_top_bs, bs, &local_err);
@@ -1168,10 +1168,12 @@ static void mirror_start_job(const char *job_id, BlockDriverState *bs,
                          BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED |
                          BLK_PERM_WRITE | BLK_PERM_GRAPH_MOD, speed,
                          creation_flags, cb, opaque, errp);
-    bdrv_unref(mirror_top_bs);
     if (!s) {
         goto fail;
     }
+    /* The block job now has a reference to this node */
+    bdrv_unref(mirror_top_bs);
+
     s->source = bs;
     s->mirror_top_bs = mirror_top_bs;
 
@@ -1242,6 +1244,10 @@ static void mirror_start_job(const char *job_id, BlockDriverState *bs,
 
 fail:
     if (s) {
+        /* Make sure this BDS does not go away until we have completed the graph
+         * changes below */
+        bdrv_ref(mirror_top_bs);
+
         g_free(s->replaces);
         blk_unref(s->target);
         block_job_unref(&s->common);
@@ -1250,6 +1256,8 @@ fail:
     bdrv_child_try_set_perm(mirror_top_bs->backing, 0, BLK_PERM_ALL,
                             &error_abort);
     bdrv_replace_node(mirror_top_bs, backing_bs(mirror_top_bs), &error_abort);
+
+    bdrv_unref(mirror_top_bs);
 }
 
 void mirror_start(const char *job_id, BlockDriverState *bs,
-- 
2.12.1

Re: [Qemu-devel] [PATCH for-2.9 1/2] block/mirror: Fix use-after-free

[Philippe Mathieu-Daudé]

nice analysis/catch

On 04/03/2017 02:51 PM, Max Reitz wrote:
> If @bs does not have any parents, the only reference to @mirror_top_bs
> will be held by the BlockJob object after the bdrv_unref() following
> block_job_create(). However, if block_job_create() fails, this reference
> will not exist and @mirror_top_bs will have been deleted when we
> goto fail.
>
> The issue comes back at all later entries to the fail label: We delete
> the BlockJob object before rolling back our changes to the node graph.
> This means that we will delete @mirror_top_bs in the process.
>
> All in all, whenever @bs does not have any parents and we go down the
> fail path we will dereference @mirror_top_bs after it has been deleted.
>
> Fix this by invoking bdrv_unref() only when block_job_create() was
> successful and by bdrv_ref()'ing @mirror_top_bs in the fail path before
> deleting the BlockJob object. Finally, bdrv_unref() it at the end of the
> fail path after we actually no longer need it.
>
> Signed-off-by: Max Reitz <mreitz@redhat.com>

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

> ---
>  block/mirror.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/block/mirror.c b/block/mirror.c
> index 9e2fecc15e..46ecd38ef0 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -1150,7 +1150,7 @@ static void mirror_start_job(const char *job_id, BlockDriverState *bs,
>      mirror_top_bs->total_sectors = bs->total_sectors;
>
>      /* bdrv_append takes ownership of the mirror_top_bs reference, need to keep
> -     * it alive until block_job_create() even if bs has no parent. */
> +     * it alive until block_job_create() succeeds even if bs has no parent. */
>      bdrv_ref(mirror_top_bs);
>      bdrv_drained_begin(bs);
>      bdrv_append(mirror_top_bs, bs, &local_err);
> @@ -1168,10 +1168,12 @@ static void mirror_start_job(const char *job_id, BlockDriverState *bs,
>                           BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED |
>                           BLK_PERM_WRITE | BLK_PERM_GRAPH_MOD, speed,
>                           creation_flags, cb, opaque, errp);
> -    bdrv_unref(mirror_top_bs);
>      if (!s) {
>          goto fail;
>      }
> +    /* The block job now has a reference to this node */
> +    bdrv_unref(mirror_top_bs);
> +
>      s->source = bs;
>      s->mirror_top_bs = mirror_top_bs;
>
> @@ -1242,6 +1244,10 @@ static void mirror_start_job(const char *job_id, BlockDriverState *bs,
>
>  fail:
>      if (s) {
> +        /* Make sure this BDS does not go away until we have completed the graph
> +         * changes below */
> +        bdrv_ref(mirror_top_bs);
> +
>          g_free(s->replaces);
>          blk_unref(s->target);
>          block_job_unref(&s->common);
> @@ -1250,6 +1256,8 @@ fail:
>      bdrv_child_try_set_perm(mirror_top_bs->backing, 0, BLK_PERM_ALL,
>                              &error_abort);
>      bdrv_replace_node(mirror_top_bs, backing_bs(mirror_top_bs), &error_abort);
> +
> +    bdrv_unref(mirror_top_bs);
>  }
>
>  void mirror_start(const char *job_id, BlockDriverState *bs,
>

[Qemu-devel] [PATCH for-2.9 2/2] iotests: Add mirror tests for orphaned source

[Max Reitz]

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 tests/qemu-iotests/041        | 46 +++++++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/041.out    |  4 ++--
 tests/qemu-iotests/iotests.py | 15 ++++++++++++++
 3 files changed, 63 insertions(+), 2 deletions(-)

diff --git a/tests/qemu-iotests/041 b/tests/qemu-iotests/041
index bc6cf782fe..2f54986434 100755
--- a/tests/qemu-iotests/041
+++ b/tests/qemu-iotests/041
@@ -966,5 +966,51 @@ class TestRepairQuorum(iotests.QMPTestCase):
         #       to check that this file is really driven by quorum
         self.vm.shutdown()
 
+# Test mirroring with a source that does not have any parents (not even a
+# BlockBackend)
+class TestOrphanedSource(iotests.QMPTestCase):
+    def setUp(self):
+        blk0 = { 'node-name': 'src',
+                 'driver': 'null-co' }
+
+        blk1 = { 'node-name': 'dest',
+                 'driver': 'null-co' }
+
+        blk2 = { 'node-name': 'dest-ro',
+                 'driver': 'null-co',
+                 'read-only': 'on' }
+
+        self.vm = iotests.VM()
+        self.vm.add_blockdev(self.qmp_to_opts(blk0))
+        self.vm.add_blockdev(self.qmp_to_opts(blk1))
+        self.vm.add_blockdev(self.qmp_to_opts(blk2))
+        self.vm.launch()
+
+    def tearDown(self):
+        self.vm.shutdown()
+
+    def test_no_job_id(self):
+        self.assert_no_active_block_jobs()
+
+        result = self.vm.qmp('blockdev-mirror', device='src', sync='full',
+                             target='dest')
+        self.assert_qmp(result, 'error/class', 'GenericError')
+
+    def test_success(self):
+        self.assert_no_active_block_jobs()
+
+        result = self.vm.qmp('blockdev-mirror', job_id='job', device='src',
+                             sync='full', target='dest')
+        self.assert_qmp(result, 'return', {})
+
+        self.complete_and_wait('job')
+
+    def test_failing_permissions(self):
+        self.assert_no_active_block_jobs()
+
+        result = self.vm.qmp('blockdev-mirror', device='src', sync='full',
+                             target='dest-ro')
+        self.assert_qmp(result, 'error/class', 'GenericError')
+
 if __name__ == '__main__':
     iotests.main(supported_fmts=['qcow2', 'qed'])
diff --git a/tests/qemu-iotests/041.out b/tests/qemu-iotests/041.out
index b67d0504a6..e30fd3b05b 100644
--- a/tests/qemu-iotests/041.out
+++ b/tests/qemu-iotests/041.out
@@ -1,5 +1,5 @@
-............................................................................
+...............................................................................
 ----------------------------------------------------------------------
-Ran 76 tests
+Ran 79 tests
 
 OK
diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index bec8eb4b8d..abcf3c10e2 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -177,6 +177,14 @@ class VM(qtest.QEMUQtestMachine):
         self._num_drives += 1
         return self
 
+    def add_blockdev(self, opts):
+        self._args.append('-blockdev')
+        if isinstance(opts, str):
+            self._args.append(opts)
+        else:
+            self._args.append(','.join(opts))
+        return self
+
     def pause_drive(self, drive, event=None):
         '''Pause drive r/w operations'''
         if not event:
@@ -235,6 +243,13 @@ class QMPTestCase(unittest.TestCase):
             output[basestr[:-1]] = obj # Strip trailing '.'
         return output
 
+    def qmp_to_opts(self, obj):
+        obj = self.flatten_qmp_object(obj)
+        output_list = list()
+        for key in obj:
+            output_list += [key + '=' + obj[key]]
+        return ','.join(output_list)
+
     def assert_qmp_absent(self, d, path):
         try:
             result = self.dictpath(d, path)
-- 
2.12.1

Re: [Qemu-devel] [PATCH for-2.9 2/2] iotests: Add mirror tests for orphaned source

[Eric Blake]

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On 04/03/2017 12:51 PM, Max Reitz wrote:
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  tests/qemu-iotests/041        | 46 +++++++++++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/041.out    |  4 ++--
>  tests/qemu-iotests/iotests.py | 15 ++++++++++++++
>  3 files changed, 63 insertions(+), 2 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [Qemu-block] [PATCH for-2.9 0/2] block/mirror: Fix use-after-free

[John Snow]

On 04/03/2017 01:51 PM, Max Reitz wrote:
> And the exciting 2.9 ride continues!
> 
> When mirroring from a BDS with no parents at all (such as those added
> with -blockdev or blockdev-add), we have a use-after-free in mirror's
> error path. The first patch of this series fixes that, the other adds a
> patch so we don't regress.
> 
> What issue will we find next? Stay tuned!
> 

Reviewed-by: John Snow <jsnow@redhat.com>

> 
> Max Reitz (2):
>   block/mirror: Fix use-after-free
>   iotests: Add mirror tests for orphaned source
> 
>  block/mirror.c                | 12 +++++++++--
>  tests/qemu-iotests/041        | 46 +++++++++++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/041.out    |  4 ++--
>  tests/qemu-iotests/iotests.py | 15 ++++++++++++++
>  4 files changed, 73 insertions(+), 4 deletions(-)
> 

Re: [Qemu-devel] [PATCH for-2.9 0/2] block/mirror: Fix use-after-free

[Kevin Wolf]

Am 03.04.2017 um 19:51 hat Max Reitz geschrieben:
> And the exciting 2.9 ride continues!
> 
> When mirroring from a BDS with no parents at all (such as those added
> with -blockdev or blockdev-add), we have a use-after-free in mirror's
> error path. The first patch of this series fixes that, the other adds a
> patch so we don't regress.
> 
> What issue will we find next? Stay tuned!

Thanks, applied to the block branch.

Kevin