The Hyper-V dynamic memory host supplies DM_UNBALLOON_REQUEST messages
with a header size and a range_count field. balloon_down() trusts
range_count and walks req->range_array without checking that the received
message contains that many ranges.
A malformed host or backend message can therefore make the guest read
past the received VMBus packet while freeing balloon ranges. Validate the
received message size and reject range_count values that exceed the
present range array before walking it.
Impact: A malicious Hyper-V host or backend can crash a guest by sending
a short unballoon request with an oversized range_count.
Fixes: 9aa8b50b2b3d ("Drivers: hv: Add Hyper-V balloon driver")
Cc: [email protected]
Assisted-by: Codex:gpt-5-5-xhigh
Signed-off-by: Michael Bommarito <[email protected]>
---
drivers/hv/hv_balloon.c | 26 ++++++++++++++++++++++++--
1 file changed, 24 insertions(+), 2 deletions(-)
diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index a848400a59a2d..f5bc8c9fea7b9 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -1337,8 +1337,23 @@ static void balloon_up(struct work_struct *dummy)
}
}
+static bool unballoon_request_valid(struct dm_unballoon_request *req,
+ u32 msg_size)
+{
+ u32 max_ranges;
+
+ if (msg_size < sizeof(*req) || req->hdr.size < sizeof(*req) ||
+ req->hdr.size > msg_size)
+ return false;
+
+ max_ranges = (req->hdr.size - sizeof(*req)) /
+ sizeof(req->range_array[0]);
+
+ return req->range_count <= max_ranges;
+}
+
static void balloon_down(struct hv_dynmem_device *dm,
- struct dm_unballoon_request *req)
+ struct dm_unballoon_request *req, u32 msg_size)
{
union dm_mem_page_range *range_array = req->range_array;
int range_count = req->range_count;
@@ -1346,6 +1361,12 @@ static void balloon_down(struct hv_dynmem_device *dm,
int i;
unsigned int prev_pages_ballooned = dm->num_pages_ballooned;
+ if (!unballoon_request_valid(req, msg_size)) {
+ pr_warn_ratelimited("Invalid unballoon request: size %u, header
size %u, range count %u\n",
+ msg_size, req->hdr.size, req->range_count);
+ return;
+ }
+
for (i = 0; i < range_count; i++) {
free_balloon_pages(dm, &range_array[i]);
complete(&dm_device.config_event);
@@ -1527,7 +1548,8 @@ static void balloon_onchannelcallback(void *context)
dm->state = DM_BALLOON_DOWN;
balloon_down(dm,
- (struct dm_unballoon_request
*)recv_buffer);
+ (struct dm_unballoon_request *)recv_buffer,
+ recvlen);
break;
case DM_MEM_HOT_ADD_REQUEST:
--
2.53.0
