From: Juergen Gross jgross@suse.com
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 --- drivers/xen/xenbus/xenbus_client.c | 24 +++++++++++------------- 1 file changed, 11 insertions(+), 13 deletions(-)
--- a/drivers/xen/xenbus/xenbus_client.c +++ b/drivers/xen/xenbus/xenbus_client.c @@ -387,7 +387,14 @@ int xenbus_grant_ring(struct xenbus_devi 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; @@ -397,23 +404,14 @@ int xenbus_grant_ring(struct xenbus_devi 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);