CVE-2026-80697: erofs: ensure valid f_path for page cache sharing
In the Linux kernel, the following vulnerability has been resolved:
erofs: ensure valid fpath 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 fpath.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: errorcode(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 backingfileopen() can be used directly.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-42.42~24.04.1 - Upgrade
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ubuntu/linux-riscv-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1~24.04.1 - Upgrade
Upgrade
ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-42.42 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1016.17 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1016.18 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
Upgrade
ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1015.16 - Upgrade
Upgrade
ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1
Event History
Frequently Asked Questions
What conditions are required to trigger the crash?
The affected system must use EROFS page cache sharing with backing files whose f_path was left NULL. A mincore operation can then dereference the missing mount path and cause a kernel NULL-pointer crash.
How can I identify a likely occurrence of this issue?
The reported failure is a kernel NULL pointer dereference in __do_sys_mincore, with the faulting address shown as 0x18. The issue was reproduced by the erofs/028 test using fincore.
What does the fix change?
The fix gives page-cache-sharing backing files valid paths, using disconnected dentries with erofs_ishare_mnt, rather than leaving f_path empty. It also allows standard backing_file_open() to be used directly.