Bug 2559788 (CVE-2026-99063)

Summary: CVE-2026-99063 kernel: dm ioctl: don't let data_start run past the buffer
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's Device Mapper (DM) subsystem. When processing certain input/output control (ioctl) requests with minimal buffer sizes, the interface fails to properly validate that the result buffer's start offset remains within the allocated memory boundaries. A local attacker with administrative privileges can exploit this flaw to cause an out-of-bounds read, leading to the disclosure of sensitive adjacent kernel memory or a system crash resulting in a Denial of Service (DoS).
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-10-23 13:38:08 UTC 
In the Linux kernel, the following vulnerability has been resolved:

dm ioctl: don't let data_start run past the buffer

struct dm_ioctl has seven bytes of trailing padding, so the smallest
buffer userspace is allowed to ask for, offsetof(struct dm_ioctl, data),
is seven bytes shorter than sizeof(struct dm_ioctl).

get_result_buffer() sets data_start to sizeof(struct dm_ioctl) without
looking at how big the buffer actually is. Ask for the minimum and
data_start ends up seven bytes past the end. Callers add it to
data_size, and ctl_ioctl() copies that much back to userspace:

  BUG: KASAN: slab-out-of-bounds in _copy_to_user+0xad/0xd0
  Read of size 312 at addr ffff8880169e4c00 by task repro-dm/140
   ctl_ioctl+0x5e3/0xcb0
   dm_ctl_ioctl+0x25/0x40
  allocated 305-byte region [ffff8880169e4c00, ffff8880169e4d31)

A DM_LIST_DEVICES with data_size set to 305 is enough to hit it, and the
seven bytes that leak are whatever sat next to the allocation.

Clamp data_start to the buffer size.

Note that this is not a security bug because the out-of-bounds read can
only be triggered by root.
Comment 1 gkamathe 2026-10-27 03:59:25 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-99063.mbox