Bug 2468143 (CVE-2026-43364)

Summary: CVE-2026-43364 kernel: ublk: fix NULL pointer dereference in ublk_ctrl_set_size()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's ublk subsystem. A local user can trigger a NULL pointer dereference by sending an UPDATE_SIZE command to a ublk device that has been added but not yet started, or one that has been stopped. This occurs due to insufficient state validation before dereferencing ub->ub_disk. Successful exploitation of this vulnerability could lead to a system crash, resulting in a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-05-08 15:01:23 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ublk: fix NULL pointer dereference in ublk_ctrl_set_size()

ublk_ctrl_set_size() unconditionally dereferences ub->ub_disk via
set_capacity_and_notify() without checking if it is NULL.

ub->ub_disk is NULL before UBLK_CMD_START_DEV completes (it is only
assigned in ublk_ctrl_start_dev()) and after UBLK_CMD_STOP_DEV runs
(ublk_detach_disk() sets it to NULL). Since the UBLK_CMD_UPDATE_SIZE
handler performs no state validation, a user can trigger a NULL pointer
dereference by sending UPDATE_SIZE to a device that has been added but
not yet started, or one that has been stopped.

Fix this by checking ub->ub_disk under ub->mutex before dereferencing
it, and returning -ENODEV if the disk is not available.
Comment 1 Keith Grant 2026-05-08 20:36:05 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050827-CVE-2026-43364-7be5@gregkh/T