CVE-2025-68356 — gfs2: Prevent recursive memory reclaim

Affected: Linux

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

gfs2: Prevent recursive memory reclaim

Function new_inode() returns a new inode with inode->i_mapping->gfp_mask set to GFP_HIGHUSER_MOVABLE. This value includes the __GFP_FS 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, gfs2_unstuff_dinode() is called inside filesystem transactions. This calls filemap_grab_folio(), 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 __GFP_FS.

The "meta" and resource group address spaces were already using GFP_NOFS as their gfp_mask (which doesn't include __GFP_FS). The default value of GFP_HIGHUSER_MOVABLE is less restrictive than GFP_NOFS, though. To avoid being overly limiting, use the default value and only knock off the __GFP_FS 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.

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CVE-2025-68356 — gfs2: Prevent recursive memory reclaim