NFS/localio: prevent direct reclaim recursion into NFS via nfs_writepages

Overview

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

NFS/localio: prevent direct reclaim recursion into NFS via nfs_writepages

LOCALIO is an NFS loopback mount optimization that avoids using the network for READ, WRITE and COMMIT if the NFS client and server are determined to be on the same system. But because LOCALIO is still fundamentally "just NFS loopback mount" it is susceptible to recursion deadlock via direct reclaim, e.g.: NFS LOCALIO down to XFS and then back into NFS via nfs_writepages.

Fix LOCALIO's potential for direct reclaim deadlock by ensuring that all its page cache allocations are done from GFP_NOFS context.

Thanks to Ben Coddington for pointing out commit ad22c7a043c2 ("xfs: prevent stack overflows from page cache allocation").

Affected

• Linux >= 70ba381e1a431245c137ed597ec6a05991c79bd9 < 9118e1cab8a5571c6a95011f77ff28480aee9cb0
• Linux >= 70ba381e1a431245c137ed597ec6a05991c79bd9 < ae26a4cf2baf0a44c538dc093504d1994b02dade
• Linux >= 70ba381e1a431245c137ed597ec6a05991c79bd9 < 6a5de0c4fc0f217eea945d3d72c34ee30d72cbc9
• Linux >= 70ba381e1a431245c137ed597ec6a05991c79bd9 < 67435d2d8a33a75f9647724952cb1b18279d2e95
• Linux 6.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.