xen/xenbus: don't let xenbus_grant_ring() remove grants in error case

stable inclusion
from stable-v5.10.105
commit 5c600371b8fd02cbbb0eb83a9f664e3f0b75c28e
bugzilla: 186480 https://gitee.com/src-openeuler/kernel/issues/I50WA6
CVE: CVE-2022-23040

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c600371b8fd02cbbb0eb83a9f664e3f0b75c28e



--------------------------------

Commit 3777ea7b upstream.

Letting xenbus_grant_ring() tear down grants in the error case is
problematic, as the other side could already have used these grants.
Calling gnttab_end_foreign_access_ref() without checking success is
resulting in an unclear situation for any caller of xenbus_grant_ring()
as in the error case the memory pages of the ring page might be
partially mapped. Freeing them would risk unwanted foreign access to
them, while not freeing them would leak memory.

In order to remove the need to undo any gnttab_grant_foreign_access()
calls, use gnttab_alloc_grant_references() to make sure no further
error can occur in the loop granting access to the ring pages.

It should be noted that this way of handling removes leaking of
grant entries in the error case, too.

This is CVE-2022-23040 / part of XSA-396.

Reported-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>