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CVE-2026-74591
mm/filemap: __filemap_add_folio() restore index before retrying
Published 2026-08-22 (2 months ago) by the Linux kernel CNA. Subsystem mm. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74591 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
In __filemap_add_folio()'s split-a-conflict loop, xas_set_order() is applied repeatedly: each application modifies xas.xa_index, rounding it down according to the split_order attempted at that stage: and if all goes as intended, it eventually (or immediately) converges on an xas_try_split() to the required folio_order, with xas.xa_index now the same as index: then xas_store() puts the new folio into the xarray there. But if a new node was needed, and GFP_NOWAIT allocation did not get one, the lock is dropped, xas_nomem() used to allocate, and sequence retried. If (that part of) the xarray is unchanged when the lock is reacquired, no problem. But what if the conflict was meanwhile resolved by another thread (perhaps even doing the same thing, inserting a folio at that same index)? Isn't there a danger of now putting our folio into the xarray at an intermediate rounded-down index? With !folio_contains() bug to follow, when CONFIG_DEBUG_VM=y is checking for that. Fix this with an xas_set_order() to restore the original xas.xa_index at the bottom of the loop, so the retry does a full re-evaluation after reacquiring the lock, and cannot reach xas_store() with the wrong index. Production was suffering from rare SIGILLs and SIGSEGVs, executable text found a page away from where it belonged, !folio_contains() bug hit when debug enabled: symptoms not seen since this patch went in.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
mm/filemap.c
- What this is
- PAGE CACHEMAINTAINERS section matched on mm/filemap.c · linux-fsdevel@vger.kernel.org · Supported
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS Debian linux-config packages
Signals
- Published
- 2026-08-22 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.65%, higher than 50.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- mm
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.15 | 6.18.45 | 4917e3ebcab5 |
| 6.15 | 7.1.9 | 267ecd2eb775 |
| 6.15 | 7.2 | 86da3f7e1e60 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- __filemap_add_folio() is reached from every page-cache insert path including nfsd vfs_iocb_iter_read() and ksmbd kernel_read() on internet-facing file servers, as well as local buffered reads, writes, and mmap faults via filemap_get_folio().
- AC:LAttack complexity, low
- An attacker controls both sides of the race by issuing concurrent reads/writes or NFS/SMB requests to the same file offsets while applying memory pressure to force xas_nomem() xa_node allocation retries after lock drops.
- PR:NPrivileges required, none
- Exploitation requires only the ability to trigger concurrent page-cache population on accessible files via network NFS/SMB reads or local syscalls; no real root, CAP_SYS_ADMIN, or init-namespace privileges are needed.
- UI:NUser interaction, none
- The corrupt insert is triggered entirely by attacker-driven concurrent I/O and memory pressure; no victim click, mount, or other interactive action beyond normal automated file access is required.
- S:UScope, unchanged
- Corruption is confined to the kernel page cache and process address spaces on the same host; it does not cross a VM, container runtime, or IOMMU security boundary to a separate authority.
- C:HConfidentiality impact, high
- Storing a folio at a rounded-down xarray index maps the wrong physical page to a file offset, enabling cross-page disclosure of file or kernel data; production saw executable text one page away from its correct location.
- I:HIntegrity impact, high
- Wrong-index folio insertion corrupts page-cache mappings and served executable content, providing a memory-corruption primitive that can alter code and data seen by userspace mappings and enable further exploitation.
- A:HAvailability impact, high
- Production systems experienced rare SIGILL and SIGSEGV crashes from corrupted mappings, and CONFIG_DEBUG_VM builds hit !folio_contains() BUG checks, demonstrating reliable kernel and process termination.