Commit d36a5c22 authored Feb 08, 2020 by Christian Schoenebeck Committed by Greg Kurz Feb 08, 2020

9pfs: validate count sent by client with T_readdir



A good 9p client sends T_readdir with "count" parameter that's sufficiently
smaller than client's initially negotiated msize (maximum message size).
We perform a check for that though to avoid the server to be interrupted
with a "Failed to encode VirtFS reply type 41" transport error message by
bad clients. This count value constraint uses msize - 11, because 11 is the
header size of R_readdir.

Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <3990d3891e8ae2074709b56449e96ab4b4b93b7d.1579567020.git.qemu_oss@crudebyte.com>
[groug: added comment ]
Signed-off-by: Greg Kurz <groug@kaod.org>

parent e16453a3

hw/9pfs/9p.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -2434,6 +2434,7 @@ static void coroutine_fn v9fs_readdir(void *opaque)
		int32_t count;
		uint32_t max_count;
		V9fsPDU *pdu = opaque;
		V9fsState *s = pdu->s;

		retval = pdu_unmarshal(pdu, offset, "dqd", &fid,
		&initial_offset, &max_count);
		@@ -2442,6 +2443,14 @@ static void coroutine_fn v9fs_readdir(void *opaque)
		}
		trace_v9fs_readdir(pdu->tag, pdu->id, fid, initial_offset, max_count);

		/* Enough space for a R_readdir header: size[4] Rreaddir tag[2] count[4] */
		if (max_count > s->msize - 11) {
		max_count = s->msize - 11;
		warn_report_once(
		"9p: bad client: T_readdir with count > msize - 11"
		);
		}

		fidp = get_fid(pdu, fid);
		if (fidp == NULL) {
		retval = -EINVAL;