In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
mm\/filemap: __filemap_add_folio() restore index before retrying<\/p>\n
In __filemap_add_folio()’s split-a-conflict loop, xas_set_order() is
\napplied repeatedly: each application modifies xas.xa_index, rounding it
\ndown according to the split_order attempted at that stage: and if all goes
\nas intended, it eventually (or immediately) converges on an
\nxas_try_split() to the required folio_order, with xas.xa_index now the
\nsame as index: then xas_store() puts the new folio into the xarray there.<\/p>\n
But if a new node was needed, and GFP_NOWAIT allocation did not get one,
\nthe lock is dropped, xas_nomem() used to allocate, and sequence retried.
\nIf (that part of) the xarray is unchanged when the lock is reacquired, no
\nproblem. But what if the conflict was meanwhile resolved by another
\nthread (perhaps even doing the same thing, inserting a folio at that same
\nindex)? Isn’t there a danger of now putting our folio into the xarray at
\nan intermediate rounded-down index? With !folio_contains() bug to follow,
\nwhen CONFIG_DEBUG_VM=y is checking for that.<\/p>\n
Fix this with an xas_set_order() to restore the original xas.xa_index at
\nthe bottom of the loop, so the retry does a full re-evaluation after
\nreacquiring the lock, and cannot reach xas_store() with the wrong index.<\/p>\n
Production was suffering from rare SIGILLs and SIGSEGVs, executable text
\nfound a page away from where it belonged, !folio_contains() bug hit when
\ndebug enabled: symptoms not seen since this patch went in.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
mm\/filemap: __filemap_add_folio() restore index before retrying<\/p>\n
In __filemap_add_folio()’s split-a-conflict loop, xas_set_order() <\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-11202","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/11202","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=11202"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=11202"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=11202"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}