[Xen-changelog] [xen-unstable] compat/gnttab: Prevent infinite loop in compat code

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
# Date 1352893537 0
# Node ID b64a7d868f06c730a444e990da1a4d816ce3f5dc
# Parent  c7a01b6450e483ca839228bf1e1e44de692e3458
compat/gnttab: Prevent infinite loop in compat code

c/s 20281:95ea2052b41b, which introduces Grant Table version 2
hypercalls introduces a vulnerability whereby the compat hypercall
handler can fall into an infinite loop.

If the watchdog is enabled, Xen will die after the timeout.

This is a security problem, XSA-24 / CVE-2012-4539.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Committed-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---


diff -r c7a01b6450e4 -r b64a7d868f06 xen/common/compat/grant_table.c
--- a/xen/common/compat/grant_table.c   Wed Nov 14 11:42:21 2012 +0000
+++ b/xen/common/compat/grant_table.c   Wed Nov 14 11:45:37 2012 +0000
@@ -318,6 +318,8 @@ int compat_grant_table_op(unsigned int c
 #undef XLAT_gnttab_get_status_frames_HNDL_frame_list
                 if ( unlikely(__copy_to_guest(cmp_uop, &cmp.get_status, 1)) )
                     rc = -EFAULT;
+                else
+                    i = 1;
             }
             break;
         }

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