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CVE-2025-40040 — mm/ksm: fix flag-dropping behavior in ksm_madvise

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

mm/ksm: fix flag-dropping behavior in ksm_madvise

syzkaller discovered the following crash: (kernel BUG)

[ 44.607039] ------------[ cut here ]------------ [ 44.607422] kernel BUG at mm/userfaultfd.c:2067! [ 44.608148] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI [ 44.608814] CPU: 1 UID: 0 PID: 2475 Comm: reproducer Not tainted 6.16.0-rc6 #1 PREEMPT(none) [ 44.609635] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 44.610695] RIP: 0010:userfaultfd_release_all+0x3a8/0x460

[ 44.617726] Call Trace: [ 44.617926] <TASK> [ 44.619284] userfaultfd_release+0xef/0x1b0 [ 44.620976] __fput+0x3f9/0xb60 [ 44.621240] fput_close_sync+0x110/0x210 [ 44.622222] __x64_sys_close+0x8f/0x120 [ 44.622530] do_syscall_64+0x5b/0x2f0 [ 44.622840] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 44.623244] RIP: 0033:0x7f365bb3f227

Kernel panics because it detects UFFD inconsistency during userfaultfd_release_all(). Specifically, a VMA which has a valid pointer to vma->vm_userfaultfd_ctx, but no UFFD flags in vma->vm_flags.

The inconsistency is caused in ksm_madvise(): when user calls madvise() with MADV_UNMEARGEABLE on a VMA that is registered for UFFD in MINOR mode, it accidentally clears all flags stored in the upper 32 bits of vma->vm_flags.

Assuming x86_64 kerne…

USN-8029-1 — linux, linux-raspi, linux-realtime vulnerabilities

Affected: Ubuntu:25.10: linux, Ubuntu:25.10: linux-raspi, Ubuntu:25.10: linux-realtime

Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system. This update corrects flaws in the following subsystems: - ARM64 architecture; - MIPS architecture; - Nios II architecture; - PA-RISC architecture; - RISC-V architecture; - S390 architecture; - Sun Sparc architecture; - x86 architecture; - Xtensa architecture; - Block layer subsystem; - Cryptographic API; - Compute Acceleration Framework; - ACPI drivers; - Drivers core; - Network block device driver; - Bluetooth drivers; - Bus devices; - Hardware random number generator core; - Character device driver; - Clock framework and drivers; - Data acquisition framework and drivers; - CPU frequency scaling framework; - Hardware crypto device drivers; - CXL (Compute Express Link) drivers; - Device frequency scaling framework; - ARM SCMI message protocol; - GPIO subsystem; - GPU drivers; - Hardware monitoring drivers; - HW tracing; - InfiniBand drivers; - Input Device (Miscellaneous) drivers; - IOMMU subsystem; - ISDN/mISDN subsystem; - Mailbox framework; - Multiple devices driver; - Media drivers; - Fastrpc Driver; - PCI Endpoint Test driver; - VMware Balloon Driver; - MOST (Media Oriented Systems Transport) drivers; - Network drivers; - Mellanox network drivers; - STMicroelectronics network drivers; - NVME drivers; - PCI subsystem; - Performance monitor drivers; - Pin…