[Xen-changelog] [xen-4.0-testing] compat/gnttab: Prevent infinite loop in compat code

[Xen patchbot-4.0-testing <patchbot@xxxxxxx>]

# HG changeset patch
# User Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
# Date 1352893595 0
# Node ID 68d7b9cc8259799d3c0d4075157578d5c704f72c
# Parent  c52d74b254dc38a0aeb1516bf1170158069e9442
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>

xen-unstable changeset: 26151:b64a7d868f06
Backport-requested-by: security@xxxxxxx
Committed-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---


diff -r c52d74b254dc -r 68d7b9cc8259 xen/common/compat/grant_table.c
--- a/xen/common/compat/grant_table.c   Wed Nov 14 11:44:46 2012 +0000
+++ b/xen/common/compat/grant_table.c   Wed Nov 14 11:46:35 2012 +0000
@@ -310,6 +310,8 @@ 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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