CVE-2024-46787 — userfaultfd: fix checks for huge PMDs

Affected: Linux

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

userfaultfd: fix checks for huge PMDs

Patch series "userfaultfd: fix races around pmd_trans_huge() check", v2.

The pmd_trans_huge() code in mfill_atomic() is wrong in three different ways depending on kernel version:

1. The pmd_trans_huge() check is racy and can lead to a BUG_ON() (if you hit the right two race windows) - I've tested this in a kernel build with some extra mdelay() calls. See the commit message for a description of the race scenario. On older kernels (before 6.5), I think the same bug can even theoretically lead to accessing transhuge page contents as a page table if you hit the right 5 narrow race windows (I haven't tested this case). 2. As pointed out by Qi Zheng, pmd_trans_huge() is not sufficient for detecting PMDs that don't point to page tables. On older kernels (before 6.5), you'd just have to win a single fairly wide race to hit this. I've tested this on 6.1 stable by racing migration (with a mdelay() patched into try_to_migrate()) against UFFDIO_ZEROPAGE - on my x86 VM, that causes a kernel oops in ptlock_ptr(). 3. On newer kernels (>=6.5), for shmem mappings, khugepaged is allowed to yank page tables out from under us (though I haven't tested that), so I think the BUG_ON() checks in mfill_atomic() are just wrong.

I decided to write two separate fixes for these (one fix for bugs 1+2, one fix for bug 3), so that the first fix can be backp…

USN-7154-1 — linux, linux-aws, linux-aws-6.8, linux-gcp, linux-gcp-6.8, linux-gke, linux-ibm, linux-lowlatency, linux-lowlatency-hwe…

Affected: Ubuntu:22.04:LTS: linux-aws-6.8, Ubuntu:22.04:LTS: linux-gcp-6.8, Ubuntu:22.04:LTS: linux-lowlatency-hwe-6.8, Ubuntu:22.04:LTS: linux-oracle-6.8, Ubuntu:24.04:LTS: linux, Ubuntu:24.04:LTS: linux-aws, Ubuntu:24.04:LTS: linux-gcp, Ubuntu:24.04:LTS: linux-gke, Ubuntu:24.04:LTS: linux-ibm, Ubuntu:24.04:LTS: linux-lowlatency and 3 more

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; - PowerPC architecture; - RISC-V architecture; - S390 architecture; - User-Mode Linux (UML); - x86 architecture; - Block layer subsystem; - Android drivers; - ATM drivers; - Drivers core; - Ublk userspace block driver; - Bluetooth drivers; - Character device driver; - Hardware crypto device drivers; - Buffer Sharing and Synchronization framework; - DMA engine subsystem; - Qualcomm firmware drivers; - GPIO subsystem; - GPU drivers; - HID subsystem; - Hardware monitoring drivers; - I2C subsystem; - I3C subsystem; - IIO subsystem; - InfiniBand drivers; - Input Device core drivers; - Input Device (Miscellaneous) drivers; - IOMMU subsystem; - IRQ chip drivers; - LED subsystem; - Mailbox framework; - Multiple devices driver; - Media drivers; - Fastrpc Driver; - VMware VMCI Driver; - MMC subsystem; - Ethernet bonding driver; - Network drivers; - Mellanox network drivers; - Microsoft Azure Network Adapter (MANA) driver; - Near Field Communication (NFC) drivers; - NVME drivers; - Device tree and open firmware driver; - Parport drivers; - PCI subsystem; - Pin controllers subsystem; - x86 platform drivers; - Power supply drivers; - Remote Processor subsystem; - S/390…

Most recent entries from all

CVE-2024-46787 — userfaultfd: fix checks for huge PMDs

USN-7154-1 — linux, linux-aws, linux-aws-6.8, linux-gcp, linux-gcp-6.8, linux-gke, linux-ibm, linux-lowlatency, linux-lowlatency-hwe…