9p/xen: check logical size for buffer size

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@kernel.org>
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Link: https://lkml.kernel.org/r/20221118135542.63400-1-asmadeus@codewreck.org
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>

diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c
index b15c64128c3e58e7c93bcfe94a3ffa28ffad2611..aaa5fd364691b0bd32957f56a36a80d4989ed7d1 100644 (file)
--- a/net/9p/trans_xen.c
+++ b/net/9p/trans_xen.c
@@ -208,6 +208,14 @@ 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;
 
@@ -217,6 +225,7 @@ static void p9_xen_response(struct work_struct *work)
                                     masked_prod, &masked_cons,
                                     XEN_9PFS_RING_SIZE(ring));
 
+recv_error:
                virt_mb();
                cons += h.size;
                ring->intf->in_cons = cons;