CVE-2025-39731 in Linux
Summary
by MITRE • 09/07/2025
In the Linux kernel, the following vulnerability has been resolved:
f2fs: vm_unmap_ram() may be called from an invalid context
When testing F2FS with xfstests using UFS backed virtual disks the kernel complains sometimes that f2fs_release_decomp_mem() calls vm_unmap_ram() from an invalid context. Example trace from f2fs/007 test:
f2fs/007 5s ... [12:59:38][ 8.902525] run fstests f2fs/007
[ 11.468026] BUG: sleeping function called from invalid context at mm/vmalloc.c:2978
[ 11.471849] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 68, name: irq/22-ufshcd
[ 11.475357] preempt_count: 1, expected: 0
[ 11.476970] RCU nest depth: 0, expected: 0
[ 11.478531] CPU: 0 UID: 0 PID: 68 Comm: irq/22-ufshcd Tainted: G W 6.16.0-rc5-xfstests-ufs-g40f92e79b0aa #9 PREEMPT(none)
[ 11.478535] Tainted: [W]=WARN
[ 11.478536] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 11.478537] Call Trace:
[ 11.478543] <TASK>
[ 11.478545] dump_stack_lvl+0x4e/0x70
[ 11.478554] __might_resched.cold+0xaf/0xbe
[ 11.478557] vm_unmap_ram+0x21/0xb0
[ 11.478560] f2fs_release_decomp_mem+0x59/0x80
[ 11.478563] f2fs_free_dic+0x18/0x1a0
[ 11.478565] f2fs_finish_read_bio+0xd7/0x290
[ 11.478570] blk_update_request+0xec/0x3b0
[ 11.478574] ? sbitmap_queue_clear+0x3b/0x60
[ 11.478576] scsi_end_request+0x27/0x1a0
[ 11.478582] scsi_io_completion+0x40/0x300
[ 11.478583] ufshcd_mcq_poll_cqe_lock+0xa3/0xe0
[ 11.478588] ufshcd_sl_intr+0x194/0x1f0
[ 11.478592] ufshcd_threaded_intr+0x68/0xb0
[ 11.478594] ? __pfx_irq_thread_fn+0x10/0x10
[ 11.478599] irq_thread_fn+0x20/0x60
[ 11.478602] ? __pfx_irq_thread_fn+0x10/0x10
[ 11.478603] irq_thread+0xb9/0x180
[ 11.478605] ? __pfx_irq_thread_dtor+0x10/0x10
[ 11.478607] ? __pfx_irq_thread+0x10/0x10
[ 11.478609] kthread+0x10a/0x230
[ 11.478614] ? __pfx_kthread+0x10/0x10
[ 11.478615] ret_from_fork+0x7e/0xd0
[ 11.478619] ? __pfx_kthread+0x10/0x10
[ 11.478621] ret_from_fork_asm+0x1a/0x30
[ 11.478623] </TASK>
This patch modifies in_task() check inside f2fs_read_end_io() to also check if interrupts are disabled. This ensures that pages are unmapped asynchronously in an interrupt handler.
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Analysis
by VulDB Data Team • 02/09/2026
The vulnerability identified as CVE-2025-39731 affects the Linux kernel's F2FS (Flash-Friendly File System) implementation and stems from improper context handling during memory unmapping operations. This flaw manifests when the f2fs_release_decomp_mem() function attempts to call vm_unmap_ram() from an invalid execution context, specifically within an interrupt handler where sleeping functions are not permitted. The issue was discovered during testing of F2FS with xfstests using UFS-backed virtual disks, indicating that the problem occurs under specific I/O workload conditions typical of storage subsystem testing.
The technical root cause involves a failure in the in_task() context validation within the f2fs_read_end_io() function. The kernel's BUG report demonstrates that vm_unmap_ram() was invoked from an interrupt context (irq/22-ufshcd) where preemption was disabled and atomic context was active, violating kernel scheduling constraints. This situation creates a critical violation of kernel execution rules where functions that may sleep cannot be called from atomic or interrupt contexts, leading to potential system instability and kernel panics. The call trace shows the execution path flows through the storage subsystem's UFS controller interrupt handling, through SCSI completion processing, and ultimately reaches the problematic memory unmapping operation.
The operational impact of this vulnerability extends beyond simple system crashes, as it represents a fundamental violation of kernel design principles and can compromise system stability during normal storage operations. When triggered, this condition can cause kernel oops messages, system hangs, or complete system crashes, particularly affecting systems using F2FS with UFS-backed storage configurations. The vulnerability affects kernel versions including 6.16.0-rc5 and potentially earlier versions, making it a critical concern for production systems that rely on F2FS or UFS storage subsystems. According to CWE classification, this represents a CWE-362: Concurrency Issue, specifically related to improper handling of atomic contexts and sleeping functions, while ATT&CK framework would categorize this under privilege escalation through kernel exploitation techniques.
The patch addressing this vulnerability modifies the in_task() check within f2fs_read_end_io() to additionally verify whether interrupts are disabled, ensuring that memory unmapping operations occur asynchronously when invoked from interrupt handlers. This fix aligns with kernel best practices for maintaining proper context boundaries and prevents the violation of atomic context constraints that could lead to system instability. The solution ensures that memory management operations are properly scheduled for asynchronous execution when required, rather than attempting to perform potentially blocking operations within interrupt contexts. System administrators should prioritize applying this patch to systems running affected kernel versions, particularly those utilizing F2FS filesystems with UFS storage backends, to prevent potential system crashes and maintain operational reliability. The mitigation approach directly addresses the underlying concurrency issue by enforcing proper context validation before memory management operations, thereby preventing the kernel from entering an inconsistent state during storage I/O processing.