crypto: perform permission checks under BQL

Move the permission API calls into driver-specific callbacks
that always run under BQL. In this case, bdrv_crypto_luks
needs to perform permission checks before and after
qcrypto_block_amend_options(). The problem is that the caller,
block_crypto_amend_options_generic_luks(), can also run in I/O
from .bdrv_co_amend(). This does not comply with Global State-I/O API split,
as permissions API must always run under BQL.

Firstly, introduce .bdrv_amend_pre_run() and .bdrv_amend_clean()
callbacks. These two callbacks are guaranteed to be invoked under
BQL, respectively before and after .bdrv_co_amend().
They take care of performing the permission checks
in the same way as they are currently done before and after
qcrypto_block_amend_options().
These callbacks are in preparation for next patch, where we
delete the original permission check. Right now they just add redundant
control.

Then, call .bdrv_amend_pre_run() before job_start in
qmp_x_blockdev_amend(), so that it will be run before the job coroutine
is created and stay in the main loop.
As a cleanup, use JobDriver's .clean() callback to call
.bdrv_amend_clean(), and run amend-specific cleanup callbacks under BQL.

After this patch, permission failures occur early in the blockdev-amend
job to update a LUKS volume's keys.  iotest 296 must now expect them in
x-blockdev-amend's QMP reply instead of waiting for the actual job to
fail later.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20220209105452.1694545-2-eesposit@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220304153729.711387-6-hreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/amend.c

@@ -53,10 +53,29 @@ static int coroutine_fn blockdev_amend_run(Job *job, Error **errp)
     return ret;
 }
 
+static int blockdev_amend_pre_run(BlockdevAmendJob *s, Error **errp)
+{
+    if (s->bs->drv->bdrv_amend_pre_run) {
+        return s->bs->drv->bdrv_amend_pre_run(s->bs, errp);
+    }
+
+    return 0;
+}
+
+static void blockdev_amend_clean(Job *job)
+{
+    BlockdevAmendJob *s = container_of(job, BlockdevAmendJob, common);
+
+    if (s->bs->drv->bdrv_amend_clean) {
+        s->bs->drv->bdrv_amend_clean(s->bs);
+    }
+}
+
 static const JobDriver blockdev_amend_job_driver = {
     .instance_size = sizeof(BlockdevAmendJob),
     .job_type      = JOB_TYPE_AMEND,
     .run           = blockdev_amend_run,
+    .clean         = blockdev_amend_clean,
 };
 
 void qmp_x_blockdev_amend(const char *job_id,
@@ -113,5 +132,11 @@ void qmp_x_blockdev_amend(const char *job_id,
     s->bs = bs,
     s->opts = QAPI_CLONE(BlockdevAmendOptions, options),
     s->force = has_force ? force : false;
+
+    if (blockdev_amend_pre_run(s, errp)) {
+        job_early_fail(&s->common);
+        return;
+    }
+
     job_start(&s->common);
 }

block/crypto.c

@@ -777,6 +777,37 @@ block_crypto_get_specific_info_luks(BlockDriverState *bs, Error **errp)
     return spec_info;
 }
 
+static int
+block_crypto_amend_prepare(BlockDriverState *bs, Error **errp)
+{
+    BlockCrypto *crypto = bs->opaque;
+    int ret;
+
+    /* apply for exclusive read/write permissions to the underlying file */
+    crypto->updating_keys = true;
+    ret = bdrv_child_refresh_perms(bs, bs->file, errp);
+    if (ret < 0) {
+        /* Well, in this case we will not be updating any keys */
+        crypto->updating_keys = false;
+    }
+    return ret;
+}
+
+static void
+block_crypto_amend_cleanup(BlockDriverState *bs)
+{
+    BlockCrypto *crypto = bs->opaque;
+    Error *errp = NULL;
+
+    /* release exclusive read/write permissions to the underlying file */
+    crypto->updating_keys = false;
+    bdrv_child_refresh_perms(bs, bs->file, &errp);
+
+    if (errp) {
+        error_report_err(errp);
+    }
+}
+
 static int
 block_crypto_amend_options_generic_luks(BlockDriverState *bs,
                                         QCryptoBlockAmendOptions *amend_options,
@@ -931,6 +962,8 @@ static BlockDriver bdrv_crypto_luks = {
     .bdrv_get_specific_info = block_crypto_get_specific_info_luks,
     .bdrv_amend_options = block_crypto_amend_options_luks,
     .bdrv_co_amend      = block_crypto_co_amend_luks,
+    .bdrv_amend_pre_run = block_crypto_amend_prepare,
+    .bdrv_amend_clean   = block_crypto_amend_cleanup,
 
     .is_format          = true,
 

include/block/block_int.h

@@ -124,6 +124,20 @@ struct BlockDriver {
      * on those children.
      */
     bool is_format;
+
+    /*
+     * This function is invoked under BQL before .bdrv_co_amend()
+     * (which in contrast does not necessarily run under the BQL)
+     * to allow driver-specific initialization code that requires
+     * the BQL, like setting up specific permission flags.
+     */
+    int (*bdrv_amend_pre_run)(BlockDriverState *bs, Error **errp);
+    /*
+     * This function is invoked under BQL after .bdrv_co_amend()
+     * to allow cleaning up what was done in .bdrv_amend_pre_run().
+     */
+    void (*bdrv_amend_clean)(BlockDriverState *bs);
+
     /*
      * Return true if @to_replace can be replaced by a BDS with the
      * same data as @bs without it affecting @bs's behavior (that is,

tests/qemu-iotests/296

@@ -174,8 +174,12 @@ class EncryptionSetupTestCase(iotests.QMPTestCase):
         }
 
         result = vm.qmp('x-blockdev-amend', **args)
-        assert result['return'] == {}
-        vm.run_job('job0')
+        iotests.log(result)
+        # Run the job only if it was created
+        event = ('JOB_STATUS_CHANGE',
+                 {'data': {'id': 'job0', 'status': 'created'}})
+        if vm.events_wait([event], timeout=0.0) is not None:
+            vm.run_job('job0')
 
     # test that when the image opened by two qemu processes,
     # neither of them can update the encryption keys

tests/qemu-iotests/296.out

@@ -1,11 +1,9 @@
 
+{"return": {}}
 {"execute": "job-dismiss", "arguments": {"id": "job0"}}
 {"return": {}}
-Job failed: Failed to get shared "consistent read" lock
-{"execute": "job-dismiss", "arguments": {"id": "job0"}}
-{"return": {}}
-Job failed: Failed to get shared "consistent read" lock
-{"execute": "job-dismiss", "arguments": {"id": "job0"}}
+{"error": {"class": "GenericError", "desc": "Failed to get shared \"consistent read\" lock"}}
+{"error": {"class": "GenericError", "desc": "Failed to get shared \"consistent read\" lock"}}
 {"return": {}}
 {"execute": "job-dismiss", "arguments": {"id": "job0"}}
 {"return": {}}
@@ -13,14 +11,9 @@ qemu-img: Failed to get shared "consistent read" lock
 Is another process using the image [TEST_DIR/test.img]?
 
 .
-Job failed: Block node is read-only
-{"execute": "job-dismiss", "arguments": {"id": "job0"}}
-{"return": {}}
-Job failed: Failed to get shared "consistent read" lock
-{"execute": "job-dismiss", "arguments": {"id": "job0"}}
-{"return": {}}
-Job failed: Failed to get shared "consistent read" lock
-{"execute": "job-dismiss", "arguments": {"id": "job0"}}
+{"error": {"class": "GenericError", "desc": "Block node is read-only"}}
+{"error": {"class": "GenericError", "desc": "Failed to get shared \"consistent read\" lock"}}
+{"error": {"class": "GenericError", "desc": "Failed to get shared \"consistent read\" lock"}}
 {"return": {}}
 {"execute": "job-dismiss", "arguments": {"id": "job0"}}
 {"return": {}}