CVE-2026-80697

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

erofs: ensure valid f_path for page cache sharing

Previously, backing files for page cache sharing were set up with fpath left as NULL (only finode was valid). It worked, but a recent mincore fix relies on f_path.mnt and crashes (found by "erofs/028" on 7.2-rc4):

BUG: kernel NULL pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: Oops: 0000 [#1] SMP PTI CPU: 3 UID: 0 PID: 675528 Comm: fincore Not tainted 7.2.0-rc4-00002-g[]-dirty #1 PREEMPT(lazy) Hardware name: Red Hat KVM, BIOS 1.16.0-4.al8 04/01/2014 RIP: 0010:__dosysmincore+0xc0/0x2c0 ...

Specify valid paths using valid disconnected dentries together with erofsisharemnt instead of leaving fpath empty, so they are more like real backing files in a pseudo filesystem and standard backingfile_open() can be used directly.