CVE-2025-68356

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

gfs2: Prevent recursive memory reclaim

Function newinode() returns a new inode with inode->imapping->gfpmask set to GFPHIGHUSER_MOVABLE. This value includes the _GFPFS flag, so allocations in that address space can recurse into filesystem memory reclaim. We don't want that to happen because it can consume a significant amount of stack memory.

Worse than that is that it can also deadlock: for example, in several places, gfs2unstuffdinode() is called inside filesystem transactions. This calls filemapgrabfolio(), which can allocate a new folio, which can trigger memory reclaim. If memory reclaim recurses into the filesystem and starts another transaction, a deadlock will ensue.

To fix these kinds of problems, prevent memory reclaim from recursing into filesystem code by making sure that the gfp_mask of inode address spaces doesn't include _GFPFS.

The "meta" and resource group address spaces were already using GFPNOFS as their gfpmask (which doesn't include __GFPFS). The default value of GFPHIGHUSERMOVABLE is less restrictive than GFPNOFS, though. To avoid being overly limiting, use the default value and only knock off the _GFPFS flag. I'm not sure if this will actually make a difference, but it also shouldn't hurt.

This patch is loosely based on commit ad22c7a043c2 ("xfs: prevent stack overflows from page cache allocation").

Fixes xfstest generic/273.