CVE-2025-37856 — btrfs: harden block_group::bg_list against list_del() races

Affected: Linux

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

btrfs: harden block_group::bg_list against list_del() races

As far as I can tell, these calls of list_del_init() on bg_list cannot run concurrently with btrfs_mark_bg_unused() or btrfs_mark_bg_to_reclaim(), as they are in transaction error paths and situations where the block group is readonly.

However, if there is any chance at all of racing with mark_bg_unused(), or a different future user of bg_list, better to be safe than sorry.

Otherwise we risk the following interleaving (bg_list refcount in parens)

T1 (some random op) T2 (btrfs_mark_bg_unused) !list_empty(&bg->bg_list); (1) list_del_init(&bg->bg_list); (1) list_move_tail (1) btrfs_put_block_group (0) btrfs_delete_unused_bgs bg = list_first_entry list_del_init(&bg->bg_list); btrfs_put_block_group(bg); (-1)

Ultimately, this results in a broken ref count that hits zero one deref early and the real final deref underflows the refcount, resulting in a WARNING.

USN-7594-1 — linux, linux-gcp, linux-raspi, linux-realtime vulnerabilities

Affected: Ubuntu:25.04: linux, Ubuntu:25.04: linux-gcp, Ubuntu:25.04: linux-raspi, Ubuntu:25.04: 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: - ARM32 architecture; - ARM64 architecture; - PowerPC architecture; - RISC-V architecture; - User-Mode Linux (UML); - x86 architecture; - Block layer subsystem; - Cryptographic API; - Compute Acceleration Framework; - ACPI drivers; - Serial ATA and Parallel ATA drivers; - Drivers core; - Ublk userspace block driver; - Bluetooth drivers; - Bus devices; - TPM device driver; - Clock framework and drivers; - CPU frequency scaling framework; - Buffer Sharing and Synchronization framework; - DMA engine subsystem; - GPU drivers; - HID subsystem; - HSI subsystem; - I2C subsystem; - I3C subsystem; - IIO subsystem; - InfiniBand drivers; - IOMMU subsystem; - IRQ chip drivers; - MCB driver; - Multiple devices driver; - Media drivers; - MemoryStick subsystem; - Multifunction device drivers; - Microchip PCI driver; - Intel Management Engine Interface driver; - PCI Endpoint Test driver; - MTD block device drivers; - Network drivers; - Ethernet bonding driver; - Mellanox network drivers; - STMicroelectronics network drivers; - NTB driver; - NVME drivers; - PCI subsystem; - Synopsys DesignWare PCIe PMU; - Mellanox platform drivers; - PWM drivers; - Remote Processor subsystem; - S/390 drivers; - SCSI subsystem; -…

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CVE-2025-37856 — btrfs: harden block_group::bg_list against list_del() races

USN-7594-1 — linux, linux-gcp, linux-raspi, linux-realtime vulnerabilities