From ee1f334f2f580ff09f7c1f83be46aa2bbb4d5f6a Mon Sep 17 00:00:00 2001 From: Ian Campbell Date: Wed, 4 Jan 2012 09:34:49 +0000 Subject: [PATCH] xen/xenbus: Reject replies with payload > XENSTORE_PAYLOAD_MAX. commit 9e7860cee18241633eddb36a4c34c7b61d8cecbc upstream. Haogang Chen found out that: There is a potential integer overflow in process_msg() that could result in cross-domain attack. body = kmalloc(msg->hdr.len + 1, GFP_NOIO | __GFP_HIGH); When a malicious guest passes 0xffffffff in msg->hdr.len, the subsequent call to xb_read() would write to a zero-length buffer. The other end of this connection is always the xenstore backend daemon so there is no guest (malicious or otherwise) which can do this. The xenstore daemon is a trusted component in the system. However this seem like a reasonable robustness improvement so we should have it. And Ian when read the API docs found that: The payload length (len field of the header) is limited to 4096 (XENSTORE_PAYLOAD_MAX) in both directions. If a client exceeds the limit, its xenstored connection will be immediately killed by xenstored, which is usually catastrophic from the client's point of view. Clients (particularly domains, which cannot just reconnect) should avoid this. so this patch checks against that instead. This also avoids a potential integer overflow pointed out by Haogang Chen. Signed-off-by: Ian Campbell Cc: Haogang Chen Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Greg Kroah-Hartman --- drivers/xen/xenbus/xenbus_xs.c | 6 ++++++ include/xen/interface/io/xs_wire.h | 3 +++ 2 files changed, 9 insertions(+) diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c index ede860f921df..a580b177eff1 100644 --- a/drivers/xen/xenbus/xenbus_xs.c +++ b/drivers/xen/xenbus/xenbus_xs.c @@ -801,6 +801,12 @@ static int process_msg(void) goto out; } + if (msg->hdr.len > XENSTORE_PAYLOAD_MAX) { + kfree(msg); + err = -EINVAL; + goto out; + } + body = kmalloc(msg->hdr.len + 1, GFP_NOIO | __GFP_HIGH); if (body == NULL) { kfree(msg); diff --git a/include/xen/interface/io/xs_wire.h b/include/xen/interface/io/xs_wire.h index f6f07aa35af5..7cdfca24eafb 100644 --- a/include/xen/interface/io/xs_wire.h +++ b/include/xen/interface/io/xs_wire.h @@ -87,4 +87,7 @@ struct xenstore_domain_interface { XENSTORE_RING_IDX rsp_cons, rsp_prod; }; +/* Violating this is very bad. See docs/misc/xenstore.txt. */ +#define XENSTORE_PAYLOAD_MAX 4096 + #endif /* _XS_WIRE_H */ -- 2.39.5