diff options
Diffstat (limited to 'system/xen/xsa/xsa236-4.9.patch')
| -rw-r--r-- | system/xen/xsa/xsa236-4.9.patch | 66 |
1 files changed, 66 insertions, 0 deletions
diff --git a/system/xen/xsa/xsa236-4.9.patch b/system/xen/xsa/xsa236-4.9.patch new file mode 100644 index 0000000000..203025dbae --- /dev/null +++ b/system/xen/xsa/xsa236-4.9.patch @@ -0,0 +1,66 @@ +From: Jan Beulich <jbeulich@suse.com> +Subject: gnttab: fix pin count / page reference race + +Dropping page references before decrementing pin counts is a bad idea +if assumptions are being made that a non-zero pin count implies a valid +page. Fix the order of operations in gnttab_copy_release_buf(), but at +the same time also remove the assertion that was found to trigger: +map_grant_ref() also has the potential of causing a race here, and +changing the order of operations there would likely be quite a bit more +involved. + +This is XSA-236. + +Reported-by: Pawel Wieczorkiewicz <wipawel@amazon.de> +Signed-off-by: Jan Beulich <jbeulich@suse.com> +Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com> + +--- a/xen/common/grant_table.c ++++ b/xen/common/grant_table.c +@@ -2330,9 +2330,20 @@ __acquire_grant_for_copy( + td = page_get_owner_and_reference(*page); + /* + * act->pin being non-zero should guarantee the page to have a +- * non-zero refcount and hence a valid owner. ++ * non-zero refcount and hence a valid owner (matching the one on ++ * record), with one exception: If the owning domain is dying we ++ * had better not make implications from pin count (map_grant_ref() ++ * updates pin counts before obtaining page references, for ++ * example). + */ +- ASSERT(td); ++ if ( td != rd || rd->is_dying ) ++ { ++ if ( td ) ++ put_page(*page); ++ *page = NULL; ++ rc = GNTST_bad_domain; ++ goto unlock_out_clear; ++ } + } + + act->pin += readonly ? GNTPIN_hstr_inc : GNTPIN_hstw_inc; +@@ -2451,6 +2462,11 @@ static void gnttab_copy_release_buf(stru + unmap_domain_page(buf->virt); + buf->virt = NULL; + } ++ if ( buf->have_grant ) ++ { ++ __release_grant_for_copy(buf->domain, buf->ptr.u.ref, buf->read_only); ++ buf->have_grant = 0; ++ } + if ( buf->have_type ) + { + put_page_type(buf->page); +@@ -2461,11 +2477,6 @@ static void gnttab_copy_release_buf(stru + put_page(buf->page); + buf->page = NULL; + } +- if ( buf->have_grant ) +- { +- __release_grant_for_copy(buf->domain, buf->ptr.u.ref, buf->read_only); +- buf->have_grant = 0; +- } + } + + static int gnttab_copy_claim_buf(const struct gnttab_copy *op, |