CVE-2026-74591

In the Linux kernel, the following vulnerability has been resolved:

mm/filemap: _filemapadd_folio() restore index before retrying

In _filemapaddfolio()'s split-a-conflict loop, xasset_order() is

applied repeatedly: each application modifies xas.xa_index, rounding it

down according to the split_order attempted at that stage: and if all goes

as intended, it eventually (or immediately) converges on an

xastrysplit() to the required folioorder, with xas.xaindex now the

same as index: then xas_store() puts the new folio into the xarray there.

But if a new node was needed, and GFP_NOWAIT allocation did not get one,

the lock is dropped, xas_nomem() used to allocate, and sequence retried. 

If (that part of) the xarray is unchanged when the lock is reacquired, no

problem.  But what if the conflict was meanwhile resolved by another

thread (perhaps even doing the same thing, inserting a folio at that same

index)?  Isn't there a danger of now putting our folio into the xarray at

an intermediate rounded-down index?  With !folio_contains() bug to follow,

when CONFIGDEBUGVM=y is checking for that.

Fix this with an xassetorder() to restore the original xas.xa_index at

the bottom of the loop, so the retry does a full re-evaluation after

reacquiring the lock, and cannot reach xas_store() with the wrong index.

Production was suffering from rare SIGILLs and SIGSEGVs, executable text

found a page away from where it belonged, !folio_contains() bug hit when

debug enabled: symptoms not seen since this patch went in.