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>

1 files changed, 33 insertions, 0 deletions

diff --git a/block/crypto.c b/block/crypto.c
index c8ba4681e2..70b2f07351 100644
--- a/block/crypto.c
+++ b/block/crypto.c
@@ -778,6 +778,37 @@ block_crypto_get_specific_info_luks(BlockDriverState *bs, Error **errp)
 }
 
 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,
                                         bool force,
@@ -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,