From: Juergen Gross jgross@suse.com
stable inclusion from linux-4.19.234 commit 8d521d960aef22781ff499e16899c30af899de8d
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Commit 3777ea7bac3113005b7180e6b9dadf16d19a5827 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: Yongqiang Liu liuyongqiang13@huawei.com Reviewed-by: Xiu Jianfeng xiujianfeng@huawei.com Reviewed-by: Jason Yan yanaijie@huawei.com Signed-off-by: Laibin Qiu qiulaibin@huawei.com --- drivers/xen/xenbus/xenbus_client.c | 24 +++++++++++------------- 1 file changed, 11 insertions(+), 13 deletions(-)
diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c index 9955892d1ea6..365cf9f5c967 100644 --- a/drivers/xen/xenbus/xenbus_client.c +++ b/drivers/xen/xenbus/xenbus_client.c @@ -368,7 +368,14 @@ int xenbus_grant_ring(struct xenbus_device *dev, void *vaddr, unsigned int nr_pages, grant_ref_t *grefs) { int err; - int i, j; + unsigned int i; + grant_ref_t gref_head; + + err = gnttab_alloc_grant_references(nr_pages, &gref_head); + if (err) { + xenbus_dev_fatal(dev, err, "granting access to ring page"); + return err; + }
for (i = 0; i < nr_pages; i++) { unsigned long gfn; @@ -378,23 +385,14 @@ int xenbus_grant_ring(struct xenbus_device *dev, void *vaddr, else gfn = virt_to_gfn(vaddr);
- err = gnttab_grant_foreign_access(dev->otherend_id, gfn, 0); - if (err < 0) { - xenbus_dev_fatal(dev, err, - "granting access to ring page"); - goto fail; - } - grefs[i] = err; + grefs[i] = gnttab_claim_grant_reference(&gref_head); + gnttab_grant_foreign_access_ref(grefs[i], dev->otherend_id, + gfn, 0);
vaddr = vaddr + XEN_PAGE_SIZE; }
return 0; - -fail: - for (j = 0; j < i; j++) - gnttab_end_foreign_access_ref(grefs[j], 0); - return err; } EXPORT_SYMBOL_GPL(xenbus_grant_ring);