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CVE-2026-68145
iomap: fix out-of-bounds bitmap_set() with zero-length range
Published 2026-08-10 (2 months ago) by the Linux kernel CNA. Subsystem fs/iomap. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-68145 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 | fixed | 6.12.101-1 | Update the kernel and reboot. Fixed in 6.12.101-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4745-1 · 2026-08-18 · text | 6.12.101-1~deb12u1 | Update the kernel and reboot. DLA-4745-1 shipped the fix on 2026-08-18, in 6.12.101-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
ifs_set_range_dirty() and ifs_set_range_uptodate() compute last_blk as (off + len - 1) >> i_blkbits. When off is 0 and len is 0, the unsigned subtraction underflows to SIZE_MAX, producing a huge last_blk and nr_blks value that causes bitmap_set() to write far beyond the ifs->state allocation. Regarding ifs_set_range_uptodate(), it is temporarily safe because len cannot be passed in as 0. However, for ifs_set_range_dirty() this is reachable from __iomap_write_end(): when copy_folio_from_iter_atomic() returns 0 (e.g. user buffer fault) and the folio is already uptodate, the guard at the top of __iomap_write_end() does not trigger because !folio_test_uptodate() is false, and iomap_set_range_dirty() is called with copied == 0. Add a !len guard to both functions before the computation, so that a zero-length range is a no-op.
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.
fs/iomap/buffered-io.c
- What this is
- FILESYSTEMS [IOMAP]MAINTAINERS section matched on fs/iomap/ · linux-xfs@vger.kernel.org · Supported
Check it on the machine
grep -wE 'CONFIG_BLOCK|CONFIG_FS_IOMAP' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
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, sid, bookworm · linux-6.12y
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switches
- CONFIG_BLOCK, CONFIG_FS_IOMAP
- Reads as
- all on means the file is compiled; any one off means it is not.
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 kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-10 (2 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.14%, higher than 2.9% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- fs/iomap
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.6 | 6.6.153 | 48829622212f |
| 6.6 | 6.12.101 | fb4fad9105c8 |
| 6.6 | 6.18.42 | 7037e7bdcd26 |
| 6.6 | 7.1.6 | c5b6a48a8a71 |
| 6.6 | 7.2 | 9c7d8f7c8994 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4745-1 | 2026-08-18 | bookworm 6.12.101-1~deb12u1 | tracker |
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:LAttack vector, local
- The bug is reached via the buffered write() path through iomap_file_buffered_write() when copy_folio_from_iter_atomic() returns 0; NFS/ksmbd server writes use kernel bvec iterators and do not hit this user-buffer fault path.
- AC:LAttack complexity, low
- An attacker can reliably trigger copied==0 by racing munmap/remap against write() on an already-uptodate folio (TOCTOU after fault_in_iov_iter_readable), controlling both sides of the race on systems where folio size exceeds filesystem block size.
- PR:LPrivileges required, low
- Only standard local write permission to a file on an iomap-backed filesystem (XFS, GFS2, FUSE writeback-cache, zonefs, NTFS) is required; no CAP_SYS_ADMIN or other elevated capability is needed beyond creating/triggering writes to attacker-writable files.
- UI:NUser interaction, none
- Exploitation requires only the attacker's own write operations to a writable file; no action by another user or administrator (such as mounting a filesystem or opening a file on the victim's behalf) is needed.
- S:UScope, unchanged
- Successful exploitation corrupts host kernel heap memory and enables local privilege escalation within the same kernel security domain; it does not inherently cross VM, container, or IOMMU boundaries.
- C:HConfidentiality impact, high
- ifs_set_range_dirty() with len==0 underflows to SIZE_MAX and bitmap_set() writes far beyond the small kzalloc_flex(ifs->state) allocation, corrupting adjacent kmalloc objects in ways that can be leveraged for arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- The out-of-bounds bitmap_set() is a large heap overwrite primitive adjacent to the iomap_folio_state allocation, enabling control of kernel data structures and arbitrary code execution via standard heap exploitation techniques.
- A:HAvailability impact, high
- The massive out-of-bounds write can immediately corrupt critical kernel heap metadata or adjacent objects, causing kernel oops/panic or unrecoverable memory corruption even before full exploitation is attempted.