On Thu, Dec 15, 2022 at 01:56:59PM -0800, Steve Sistare wrote: > When a vfio container is preserved across exec, the task does not change, > but it gets a new mm with locked_vm=0. If the user later unmaps a dma > mapping, locked_vm underflows to a large unsigned value, and a subsequent > dma map request fails with ENOMEM in __account_locked_vm. > > To avoid underflow, grab and save the mm at the time a dma is mapped. > Use that mm when adjusting locked_vm, rather than re-acquiring the saved > task's mm, which may have changed. If the saved mm is dead, do nothing. > > Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx> > --- > drivers/vfio/vfio_iommu_type1.c | 17 ++++++++++------- > 1 file changed, 10 insertions(+), 7 deletions(-) Add fixes lines and a CC stable The subject should be more like 'vfio/typ1: Prevent corruption of mm->locked_vm via exec()' > @@ -1687,6 +1689,8 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu, > get_task_struct(current->group_leader); > dma->task = current->group_leader; > dma->lock_cap = capable(CAP_IPC_LOCK); > + dma->mm = dma->task->mm; This should be current->mm, current->group_leader->mm is not quite the same thing (and maybe another bug, I'm not sure) Jason
