From 1104d83c726d2b20f9cec7b99ab3570a2fdbd46d Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Wed, 8 Nov 2017 15:56:58 -0600 Subject: [PATCH] nbd-client: Refuse read-only client with BDRV_O_RDWR 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 Message-Id: <20171108215703.9295-3-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy --- block/nbd-client.c | 9 +++++++++ tests/qemu-iotests/058 | 8 ++++---- tests/qemu-iotests/140 | 4 ++-- tests/qemu-iotests/147 | 1 + 4 files changed, 16 insertions(+), 6 deletions(-) diff --git a/block/nbd-client.c b/block/nbd-client.c index de6c153328..daa4392531 100644 --- a/block/nbd-client.c +++ b/block/nbd-client.c @@ -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; diff --git a/tests/qemu-iotests/058 b/tests/qemu-iotests/058 index 2253c6a6d1..5eb8784669 100755 --- a/tests/qemu-iotests/058 +++ b/tests/qemu-iotests/058 @@ -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" diff --git a/tests/qemu-iotests/140 b/tests/qemu-iotests/140 index f89d0d6789..a8fc95145c 100755 --- a/tests/qemu-iotests/140 +++ b/tests/qemu-iotests/140 @@ -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 diff --git a/tests/qemu-iotests/147 b/tests/qemu-iotests/147 index db34838cd0..90f40ed245 100755 --- a/tests/qemu-iotests/147 +++ b/tests/qemu-iotests/147 @@ -43,6 +43,7 @@ class NBDBlockdevAddBase(iotests.QMPTestCase): 'driver': 'raw', 'file': { 'driver': 'nbd', + 'read-only': True, 'server': address } } if export is not None: