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nbd-client: Refuse read-only client with BDRV_O_RDWR

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The NBD spec says that clients should not try to write/trim to
an export advertised as read-only by the server.  But we failed
to check that, and would allow the block layer to use NBD with
BDRV_O_RDWR even when the server is read-only, which meant we
were depending on the server sending a proper EPERM failure for
various commands, and also exposes a leaky abstraction: using
qemu-io in read-write mode would succeed on 'w -z 0 0' because
of local short-circuiting logic, but 'w 0 0' would send a
request over the wire (where it then depends on the server, and
fails at least for qemu-nbd but might pass for other NBD
implementations).

With this patch, a client MUST request read-only mode to access
a server that is doing a read-only export, or else it will get
a message like:

can't open device nbd://localhost:10809/foo: request for write access conflicts with read-only export

It is no longer possible to even attempt writes over the wire
(including the corner case of 0-length writes), because the block
layer enforces the explicit read-only request; this matches the
behavior of qcow2 when backed by a read-only POSIX file.

Fix several iotests to comply with the new behavior (since
qemu-nbd of an internal snapshot, as well as nbd-server-add over QMP,
default to a read-only export, we must tell blockdev-add/qemu-io to
set up a read-only client).

CC: qemu-stable@nongnu.org
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20171108215703.9295-3-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
This commit is contained in:
Eric Blake 2017-11-08 15:56:58 -06:00
parent e659fb3b99
commit 1104d83c72
4 changed files with 16 additions and 6 deletions
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9
block/nbd-client.c
View file

@ -697,6 +697,7 @@ int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t offset,
.len = bytes,
};
assert(!(client->info.flags & NBD_FLAG_READ_ONLY));
if (flags & BDRV_REQ_FUA) {
assert(client->info.flags & NBD_FLAG_SEND_FUA);
request.flags |= NBD_CMD_FLAG_FUA;
@ -717,6 +718,7 @@ int nbd_client_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
.len = bytes,
};
assert(!(client->info.flags & NBD_FLAG_READ_ONLY));
if (!(client->info.flags & NBD_FLAG_SEND_WRITE_ZEROES)) {
return -ENOTSUP;
}
@ -756,6 +758,7 @@ int nbd_client_co_pdiscard(BlockDriverState *bs, int64_t offset, int bytes)
.len = bytes,
};
assert(!(client->info.flags & NBD_FLAG_READ_ONLY));
if (!(client->info.flags & NBD_FLAG_SEND_TRIM)) {
return 0;
}
@ -814,6 +817,12 @@ int nbd_client_init(BlockDriverState *bs,
logout("Failed to negotiate with the NBD server\n");
return ret;
}
if (client->info.flags & NBD_FLAG_READ_ONLY &&
!bdrv_is_read_only(bs)) {
error_setg(errp,
"request for write access conflicts with read-only export");
return -EACCES;
}
if (client->info.flags & NBD_FLAG_SEND_FUA) {
bs->supported_write_flags = BDRV_REQ_FUA;
bs->supported_zero_flags |= BDRV_REQ_FUA;

8
tests/qemu-iotests/058
View file

@ -117,15 +117,15 @@ _export_nbd_snapshot sn1
echo
echo "== verifying the exported snapshot with patterns, method 1 =="
$QEMU_IO_NBD -c 'read -P 0xa 0x1000 0x1000' "$nbd_snapshot_img" | _filter_qemu_io
$QEMU_IO_NBD -c 'read -P 0xb 0x2000 0x1000' "$nbd_snapshot_img" | _filter_qemu_io
$QEMU_IO_NBD -r -c 'read -P 0xa 0x1000 0x1000' "$nbd_snapshot_img" | _filter_qemu_io
$QEMU_IO_NBD -r -c 'read -P 0xb 0x2000 0x1000' "$nbd_snapshot_img" | _filter_qemu_io
_export_nbd_snapshot1 sn1
echo
echo "== verifying the exported snapshot with patterns, method 2 =="
$QEMU_IO_NBD -c 'read -P 0xa 0x1000 0x1000' "$nbd_snapshot_img" | _filter_qemu_io
$QEMU_IO_NBD -c 'read -P 0xb 0x2000 0x1000' "$nbd_snapshot_img" | _filter_qemu_io
$QEMU_IO_NBD -r -c 'read -P 0xa 0x1000 0x1000' "$nbd_snapshot_img" | _filter_qemu_io
$QEMU_IO_NBD -r -c 'read -P 0xb 0x2000 0x1000' "$nbd_snapshot_img" | _filter_qemu_io
$QEMU_IMG convert "$TEST_IMG" -l sn1 -O qcow2 "$converted_image"

4
tests/qemu-iotests/140
View file

@ -78,7 +78,7 @@ _send_qemu_cmd $QEMU_HANDLE \
'arguments': { 'device': 'drv' }}" \
'return'
$QEMU_IO_PROG -f raw -c 'read -P 42 0 64k' \
$QEMU_IO_PROG -f raw -r -c 'read -P 42 0 64k' \
"nbd+unix:///drv?socket=$TEST_DIR/nbd" 2>&1 \
| _filter_qemu_io | _filter_nbd
@ -87,7 +87,7 @@ _send_qemu_cmd $QEMU_HANDLE \
'arguments': { 'device': 'drv' }}" \
'return'
$QEMU_IO_PROG -f raw -c close \
$QEMU_IO_PROG -f raw -r -c close \
"nbd+unix:///drv?socket=$TEST_DIR/nbd" 2>&1 \
| _filter_qemu_io | _filter_nbd

1
tests/qemu-iotests/147
View file

@ -43,6 +43,7 @@ class NBDBlockdevAddBase(iotests.QMPTestCase):
'driver': 'raw',
'file': {
'driver': 'nbd',
'read-only': True,
'server': address
} }
if export is not None: