From 009cd8665095a04115940704d680a52dcc49d489 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Mon, 25 Sep 2023 14:22:31 -0500 Subject: nbd/server: Support a request payload Upcoming additions to support NBD 64-bit effect lengths allow for the possibility to distinguish between payload length (capped at 32M) and effect length (64 bits, although we generally assume 63 bits because of off_t limitations). Without that extension, only the NBD_CMD_WRITE request has a payload; but with the extension, it makes sense to allow at least NBD_CMD_BLOCK_STATUS to have both a payload and effect length in a future patch (where the payload is a limited-size struct that in turn gives the real effect length as well as a subset of known ids for which status is requested). Other future NBD commands may also have a request payload, so the 64-bit extension introduces a new NBD_CMD_FLAG_PAYLOAD_LEN that distinguishes between whether the header length is a payload length or an effect length, rather than hard-coding the decision based on the command. According to the spec, a client should never send a command with a payload without the negotiation phase proving such extension is available. So in the unlikely event the bit is set or cleared incorrectly, the client is already at fault; if the client then provides the payload, we can gracefully consume it off the wire and fail the command with NBD_EINVAL (subsequent checks for magic numbers ensure we are still in sync), while if the client fails to send payload we block waiting for it (basically deadlocking our connection to the bad client, but not negatively impacting our ability to service other clients, so not a security risk). Note that we do not support the payload version of BLOCK_STATUS yet. This patch also fixes a latent bug introduced in b2578459: once request->len can be 64 bits, assigning it to a 32-bit payload_len can cause wraparound to 0 which then sets req->complete prematurely; thankfully, the bug was not possible back then (it takes this and later patches to even allow request->len larger than 32 bits; and since previously the only 'payload_len = request->len' assignment was in NBD_CMD_WRITE which also sets check_length, which in turn rejects lengths larger than 32M before relying on any possibly-truncated value stored in payload_len). Signed-off-by: Eric Blake Message-ID: <20230925192229.3186470-15-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy [eblake: enhance comment on handling client error, fix type bug] Signed-off-by: Eric Blake --- nbd/server.c | 42 +++++++++++++++++++++++++++++++++++++----- nbd/trace-events | 1 + 2 files changed, 38 insertions(+), 5 deletions(-) (limited to 'nbd') diff --git a/nbd/server.c b/nbd/server.c index 7a6f95071f..56e9b41828 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -2322,10 +2322,12 @@ static int coroutine_fn nbd_co_receive_request(NBDRequestData *req, Error **errp) { NBDClient *client = req->client; + bool extended_with_payload; bool check_length = false; bool check_rofs = false; bool allocate_buffer = false; - unsigned payload_len = 0; + bool payload_okay = false; + uint64_t payload_len = 0; int valid_flags = NBD_CMD_FLAG_FUA; int ret; @@ -2338,6 +2340,13 @@ static int coroutine_fn nbd_co_receive_request(NBDRequestData *req, trace_nbd_co_receive_request_decode_type(request->cookie, request->type, nbd_cmd_lookup(request->type)); + extended_with_payload = client->mode >= NBD_MODE_EXTENDED && + request->flags & NBD_CMD_FLAG_PAYLOAD_LEN; + if (extended_with_payload) { + payload_len = request->len; + check_length = true; + } + switch (request->type) { case NBD_CMD_DISC: /* Special case: we're going to disconnect without a reply, @@ -2354,6 +2363,15 @@ static int coroutine_fn nbd_co_receive_request(NBDRequestData *req, break; case NBD_CMD_WRITE: + if (client->mode >= NBD_MODE_EXTENDED) { + if (!extended_with_payload) { + /* The client is noncompliant. Trace it, but proceed. */ + trace_nbd_co_receive_ext_payload_compliance(request->from, + request->len); + } + valid_flags |= NBD_CMD_FLAG_PAYLOAD_LEN; + } + payload_okay = true; payload_len = request->len; check_length = true; allocate_buffer = true; @@ -2395,6 +2413,16 @@ static int coroutine_fn nbd_co_receive_request(NBDRequestData *req, request->len, NBD_MAX_BUFFER_SIZE); return -EINVAL; } + if (payload_len && !payload_okay) { + /* + * For now, we don't support payloads on other commands; but + * we can keep the connection alive by ignoring the payload. + * We will fail the command later with NBD_EINVAL for the use + * of an unsupported flag (and not for access beyond bounds). + */ + assert(request->type != NBD_CMD_WRITE); + request->len = 0; + } if (allocate_buffer) { /* READ, WRITE */ req->data = blk_try_blockalign(client->exp->common.blk, @@ -2405,10 +2433,14 @@ static int coroutine_fn nbd_co_receive_request(NBDRequestData *req, } } if (payload_len) { - /* WRITE */ - assert(req->data); - ret = nbd_read(client->ioc, req->data, payload_len, - "CMD_WRITE data", errp); + if (payload_okay) { + /* WRITE */ + assert(req->data); + ret = nbd_read(client->ioc, req->data, payload_len, + "CMD_WRITE data", errp); + } else { + ret = nbd_drop(client->ioc, payload_len, errp); + } if (ret < 0) { return -EIO; } diff --git a/nbd/trace-events b/nbd/trace-events index f9dccfcfb4..c1a3227613 100644 --- a/nbd/trace-events +++ b/nbd/trace-events @@ -71,6 +71,7 @@ nbd_co_send_extents(uint64_t cookie, unsigned int extents, uint32_t id, uint64_t nbd_co_send_chunk_error(uint64_t cookie, int err, const char *errname, const char *msg) "Send structured error reply: cookie = %" PRIu64 ", error = %d (%s), msg = '%s'" nbd_co_receive_request_decode_type(uint64_t cookie, uint16_t type, const char *name) "Decoding type: cookie = %" PRIu64 ", type = %" PRIu16 " (%s)" nbd_co_receive_request_payload_received(uint64_t cookie, uint64_t len) "Payload received: cookie = %" PRIu64 ", len = %" PRIu64 +nbd_co_receive_ext_payload_compliance(uint64_t from, uint64_t len) "client sent non-compliant write without payload flag: from=0x%" PRIx64 ", len=0x%" PRIx64 nbd_co_receive_align_compliance(const char *op, uint64_t from, uint64_t len, uint32_t align) "client sent non-compliant unaligned %s request: from=0x%" PRIx64 ", len=0x%" PRIx64 ", align=0x%" PRIx32 nbd_trip(void) "Reading request" -- cgit v1.2.3