CVE-2025-39966
Full vulnerability record from the local CVENow database.
Description
In the Linux kernel, the following vulnerability has been resolved: iommufd: Fix race during abort for file descriptors fput() doesn't actually call file_operations release() synchronously, it puts the file on a work queue and it will be released eventually. This is normally fine, except for iommufd the file and the iommufd_object are tied to gether. The file has the object as it's private_data and holds a users refcount, while the object is expected to remain alive as long as the file is. When the allocation of a new object aborts before installing the file it will fput() the file and then go on to immediately kfree() the obj. This causes a UAF once the workqueue completes the fput() and tries to decrement the users refcount. Fix this by putting the core code in charge of the file lifetime, and call __fput_sync() during abort to ensure that release() is called before kfree. __fput_sync() is a bit too tricky to open code in all the object implementations. Instead the objects tell the core code where the file pointer is and the core will take care of the life cycle. If the object is successfully allocated then the file will hold a users refcount and the iommufd_object cannot be destroyed. It is worth noting that close(); ioctl(IOMMU_DESTROY); doesn't have an issue because close() is already using a synchronous version of fput(). The UAF looks like this: BUG: KASAN: slab-use-after-free in iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376 Write of size 4 at addr ffff888059c97804 by task syz.0.46/6164 CPU: 0 UID: 0 PID: 6164 Comm: syz.0.46 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline] print_report+0xcd/0x630 mm/kasan/report.c:482 kasan_report+0xe0/0x110 mm/kasan/report.c:595 check_region_inline mm/kasan/generic.c:183 [inline] kasan_check_range+0x100/0x1b0 mm/kasan/generic.c:189 instrument_atomic_read_write include/linux/instrumented.h:96 [inline] atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline] __refcount_dec include/linux/refcount.h:455 [inline] refcount_dec include/linux/refcount.h:476 [inline] iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376 __fput+0x402/0xb70 fs/file_table.c:468 task_work_run+0x14d/0x240 kernel/task_work.c:227 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] exit_to_user_mode_loop+0xeb/0x110 kernel/entry/common.c:43 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline] syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline] do_syscall_64+0x41c/0x4c0 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f
View original CVE JSON
{
"id": "CVE-2025-39966",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2025-10-15T08:15:34.043",
"lastModified": "2026-10-19T21:10:00.160",
"vulnStatus": "Modified",
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\niommufd: Fix race during abort for file descriptors\n\nfput() doesn't actually call file_operations release() synchronously, it\nputs the file on a work queue and it will be released eventually.\n\nThis is normally fine, except for iommufd the file and the iommufd_object\nare tied to gether. The file has the object as it's private_data and holds\na users refcount, while the object is expected to remain alive as long as\nthe file is.\n\nWhen the allocation of a new object aborts before installing the file it\nwill fput() the file and then go on to immediately kfree() the obj. This\ncauses a UAF once the workqueue completes the fput() and tries to\ndecrement the users refcount.\n\nFix this by putting the core code in charge of the file lifetime, and call\n__fput_sync() during abort to ensure that release() is called before\nkfree. __fput_sync() is a bit too tricky to open code in all the object\nimplementations. Instead the objects tell the core code where the file\npointer is and the core will take care of the life cycle.\n\nIf the object is successfully allocated then the file will hold a users\nrefcount and the iommufd_object cannot be destroyed.\n\nIt is worth noting that close(); ioctl(IOMMU_DESTROY); doesn't have an\nissue because close() is already using a synchronous version of fput().\n\nThe UAF looks like this:\n\n BUG: KASAN: slab-use-after-free in iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376\n Write of size 4 at addr ffff888059c97804 by task syz.0.46/6164\n\n CPU: 0 UID: 0 PID: 6164 Comm: syz.0.46 Not tainted syzkaller #0 PREEMPT(full)\n Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025\n Call Trace:\n <TASK>\n __dump_stack lib/dump_stack.c:94 [inline]\n dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120\n print_address_description mm/kasan/report.c:378 [inline]\n print_report+0xcd/0x630 mm/kasan/report.c:482\n kasan_report+0xe0/0x110 mm/kasan/report.c:595\n check_region_inline mm/kasan/generic.c:183 [inline]\n kasan_check_range+0x100/0x1b0 mm/kasan/generic.c:189\n instrument_atomic_read_write include/linux/instrumented.h:96 [inline]\n atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]\n __refcount_dec include/linux/refcount.h:455 [inline]\n refcount_dec include/linux/refcount.h:476 [inline]\n iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376\n __fput+0x402/0xb70 fs/file_table.c:468\n task_work_run+0x14d/0x240 kernel/task_work.c:227\n resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]\n exit_to_user_mode_loop+0xeb/0x110 kernel/entry/common.c:43\n exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]\n syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]\n syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]\n do_syscall_64+0x41c/0x4c0 arch/x86/entry/syscall_64.c:100\n entry_SYSCALL_64_after_hwframe+0x77/0x7f"
},
{
"lang": "es",
"value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\niommufd: Solucionar condición de carrera durante el aborto para descriptores de archivo\n\nfput() en realidad no llama a file_operations release() de forma síncrona, sino que pone el archivo en una cola de trabajo y se liberará eventualmente.\n\nEsto normalmente está bien, excepto para iommufd, donde el archivo y el iommufd_object están vinculados. El archivo tiene el objeto como su private_data y mantiene un refcount de usuarios, mientras que se espera que el objeto permanezca vivo mientras lo esté el archivo.\n\nCuando la asignación de un nuevo objeto aborta antes de instalar el archivo, hará fput() del archivo y luego procederá a kfree() inmediatamente el objeto. Esto causa un UAF una vez que la cola de trabajo completa el fput() e intenta decrementar el refcount de usuarios.\n\nSolucione esto poniendo el código central a cargo de la vida útil del archivo, y llamando a __fput_sync() durante el aborto para asegurar que release() se llame antes de kfree. __fput_sync() es un poco demasiado complicado para codificar abiertamente en todas las implementaciones de objetos. En su lugar, los objetos le dicen al código central dónde está el puntero del archivo y el núcleo se encargará del ciclo de vida.\n\nSi el objeto se asigna con éxito, entonces el archivo mantendrá un refcount de usuarios y el iommufd_object no podrá ser destruido.\n\nCabe señalar que close(); ioctl(IOMMU_DESTROY); no tiene un problema porque close() ya está usando una versión síncrona de fput().\n\nEl UAF se ve así:\n\n BUG: KASAN: uso después de liberación de slab en iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376\n Escritura de tamaño 4 en la dirección ffff888059c97804 por la tarea syz.0.46/6164\n\n CPU: 0 UID: 0 PID: 6164 Comm: syz.0.46 Not tainted syzkaller #0 PREEMPT(full)\n Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025\n Traza de Llamada:\n <TASK>\n __dump_stack lib/dump_stack.c:94 [inline]\n dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120\n print_address_description mm/kasan/report.c:378 [inline]\n print_report+0xcd/0x630 mm/kasan/report.c:482\n kasan_report+0xe0/0x110 mm/kasan/report.c:595\n check_region_inline mm/kasan/generic.c:183 [inline]\n kasan_check_range+0x100/0x1b0 mm/kasan/generic.c:189\n instrument_atomic_read_write include/linux/instrumented.h:96 [inline]\n atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]\n __refcount_dec include/linux/refcount.h:455 [inline]\n refcount_dec include/linux/refcount.h:476 [inline]\n iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376\n __fput+0x402/0xb70 fs/file_table.c:468\n task_work_run+0x14d/0x240 kernel/task_work.c:227\n resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]\n exit_to_user_mode_loop+0xeb/0x110 kernel/entry/common.c:43\n exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]\n syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]\n syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]\n do_syscall_64+0x41c/0x4c0 arch/x86/entry/syscall_64.c:100\n entry_SYSCALL_64_after_hwframe+0x77/0x7f"
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"source": "[email protected]",
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"description": [
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