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nbd: Don't send oversize strings

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Qemu as server currently won't accept export names larger than 256
bytes, nor create dirty bitmap names longer than 1023 bytes, so most
uses of qemu as client or server have no reason to get anywhere near
the NBD spec maximum of a 4k limit per string.

However, we weren't actually enforcing things, ignoring when the
remote side violates the protocol on input, and also having several
code paths where we send oversize strings on output (for example,
qemu-nbd --description could easily send more than 4k).  Tighten
things up as follows:

client:
- Perform bounds check on export name and dirty bitmap request prior
  to handing it to server
- Validate that copied server replies are not too long (ignoring
  NBD_INFO_* replies that are not copied is not too bad)
server:
- Perform bounds check on export name and description prior to
  advertising it to client
- Reject client name or metadata query that is too long
- Adjust things to allow full 4k name limit rather than previous
  256 byte limit

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20191114024635.11363-4-eblake@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
This commit is contained in:
Eric Blake 2019-11-13 20:46:34 -06:00
parent cf7c49cf6a
commit 93676c88d7
6 changed files with 58 additions and 12 deletions
Download patch file Download diff file Expand all files Collapse all files

10
block/nbd.c
View file

@ -1832,6 +1832,10 @@ static int nbd_process_options(BlockDriverState *bs, QDict *options,
}
s->export = g_strdup(qemu_opt_get(opts, "export"));
if (s->export && strlen(s->export) > NBD_MAX_STRING_SIZE) {
error_setg(errp, "export name too long to send to server");
goto error;
}
s->tlscredsid = g_strdup(qemu_opt_get(opts, "tls-creds"));
if (s->tlscredsid) {
@ -1849,6 +1853,11 @@ static int nbd_process_options(BlockDriverState *bs, QDict *options,
}
s->x_dirty_bitmap = g_strdup(qemu_opt_get(opts, "x-dirty-bitmap"));
if (s->x_dirty_bitmap && strlen(s->x_dirty_bitmap) > NBD_MAX_STRING_SIZE) {
error_setg(errp, "x-dirty-bitmap query too long to send to server");
goto error;
}
s->reconnect_delay = qemu_opt_get_number(opts, "reconnect-delay", 0);
ret = 0;
@ -1859,6 +1868,7 @@ static int nbd_process_options(BlockDriverState *bs, QDict *options,
qapi_free_SocketAddress(s->saddr);
g_free(s->export);
g_free(s->tlscredsid);
g_free(s->x_dirty_bitmap);
}
qemu_opts_del(opts);
return ret;