Affected: Alpaquita:23: linux-lts, Alpaquita:25: linux-lts, Alpaquita:stream: linux-lts

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

bpf: Fix use-after-free on mm_struct in bpf_find_vma()

bpf_find_vma() reads task->mm and calls mmap_read_trylock(mm) without holding a reference on the mm. On a foreign task, a concurrent exit_mm() can free the mm_struct between the lockless read and the trylock, resulting in a use-after-free. mm_struct is not SLAB_TYPESAFE_BY_RCU.

For the current task, task->mm is stable. For a foreign task, pin the mm under task->alloc_lock and release it with mmput_async(), mirroring commit d8e27d2d22b6 ("bpf: fix mm lifecycle in open-coded task_vma iterator"). Use spin_trylock() instead of get_task_mm() so BPF context does not block on alloc_lock. Reject irqs-disabled contexts and !CONFIG_MMU on the foreign-task path because dropping the mm reference is not safe there.

Race:

CPU0 (BPF program) CPU1 (exiting task) ============================ ========================== bpf_find_vma(foreign_task): mm = task->mm exit_mm(): task->mm = NULL mmput(mm) -> frees mm_struct mmap_read_trylock(mm) // UAF on mm

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

bpf: Fix use-after-free on mm_struct in bpf_find_vma()

bpf_find_vma() reads task->mm and calls mmap_read_trylock(mm) without holding a reference on the mm. On a foreign task, a concurrent exit_mm() can free the mm_struct between the lockless read and the trylock, resulting in a use-after-free. mm_struct is not SLAB_TYPESAFE_BY_RCU.

For the current task, task->mm is stable. For a foreign task, pin the mm under task->alloc_lock and release it with mmput_async(), mirroring commit d8e27d2d22b6 ("bpf: fix mm lifecycle in open-coded task_vma iterator"). Use spin_trylock() instead of get_task_mm() so BPF context does not block on alloc_lock. Reject irqs-disabled contexts and !CONFIG_MMU on the foreign-task path because dropping the mm reference is not safe there.

Race:

CPU0 (BPF program) CPU1 (exiting task) ============================ ========================== bpf_find_vma(foreign_task): mm = task->mm exit_mm(): task->mm = NULL mmput(mm) -> frees mm_struct mmap_read_trylock(mm) // UAF on mm

kernel-devel-7.2.8-1.1 on GA media

Affected: Ubuntu:16.04:LTS: linux-hwe-edge, Ubuntu:18.04:LTS: linux-aws-5.0, Ubuntu:18.04:LTS: linux-aws-5.3, Ubuntu:18.04:LTS: linux-azure, Ubuntu:18.04:LTS: linux-azure-5.3, Ubuntu:18.04:LTS: linux-azure-edge, Ubuntu:18.04:LTS: linux-gcp, Ubuntu:18.04:LTS: linux-gcp-5.3, Ubuntu:18.04:LTS: linux-gke-4.15, Ubuntu:18.04:LTS: linux-gke-5.4 and 154 more

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix use-after-free on mm_struct in bpf_find_vma() bpf_find_vma() reads task->mm and calls mmap_read_trylock(mm) without holding a reference on the mm. On a foreign task, a concurrent exit_mm() can free the mm_struct between the lockless read and the trylock, resulting in a use-after-free. mm_struct is not SLAB_TYPESAFE_BY_RCU. For the current task, task->mm is stable. For a foreign task, pin the mm under task->alloc_lock and release it with mmput_async(), mirroring commit d8e27d2d22b6 ("bpf: fix mm lifecycle in open-coded task_vma iterator"). Use spin_trylock() instead of get_task_mm() so BPF context does not block on alloc_lock. Reject irqs-disabled contexts and !CONFIG_MMU on the foreign-task path because dropping the mm reference is not safe there. Race: CPU0 (BPF program) CPU1 (exiting task) ============================ ========================== bpf_find_vma(foreign_task): mm = task->mm exit_mm(): task->mm = NULL mmput(mm) -> frees mm_struct mmap_read_trylock(mm) // UAF on mm