[PATCH AUTOSEL 4.19 11/12] 9p/xen: check logical size for buffer size

[Sasha Levin]

From: Dominique Martinet <asmadeus@xxxxxxxxxxxxx>

[ Upstream commit 391c18cf776eb4569ecda1f7794f360fe0a45a26 ]

trans_xen did not check the data fits into the buffer before copying
from the xen ring, but we probably should.
Add a check that just skips the request and return an error to
userspace if it did not fit

Tested-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Reviewed-by: Christian Schoenebeck <linux_oss@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20221118135542.63400-1-asmadeus@xxxxxxxxxxxxx
Signed-off-by: Dominique Martinet <asmadeus@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/9p/trans_xen.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c
index ac60ddfcd88b..6459c2356ff9 100644
--- a/net/9p/trans_xen.c
+++ b/net/9p/trans_xen.c
@@ -230,6 +230,14 @@ static void p9_xen_response(struct work_struct *work)
 			continue;
 		}
 
+		if (h.size > req->rc.capacity) {
+			dev_warn(&priv->dev->dev,
+				 "requested packet size too big: %d for tag %d with capacity %zd\n",
+				 h.size, h.tag, req->rc.capacity);
+			req->status = REQ_STATUS_ERROR;
+			goto recv_error;
+		}
+
 		memcpy(&req->rc, &h, sizeof(h));
 		req->rc.offset = 0;
 
@@ -239,6 +247,7 @@ static void p9_xen_response(struct work_struct *work)
 				     masked_prod, &masked_cons,
 				     XEN_9PFS_RING_SIZE);
 
+recv_error:
 		virt_mb();
 		cons += h.size;
 		ring->intf->in_cons = cons;
-- 
2.35.1