Re: [PATCH stable 4.4 v2] coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping

[Michal Hocko]

Just a heads up. Ajay Kaher has noticed that mlx4 driver is missing the
check in 4.14 [1] and 4.4 seems to have the same problem. I will wait
for more review before reposting v3. The incremental diff is:

diff --git a/drivers/infiniband/hw/mlx4/main.c b/drivers/infiniband/hw/mlx4/main.c
index 67c4c73343d4..6968154a073e 100644
--- a/drivers/infiniband/hw/mlx4/main.c
+++ b/drivers/infiniband/hw/mlx4/main.c
@@ -1042,6 +1042,8 @@ static void mlx4_ib_disassociate_ucontext(struct ib_ucontext *ibcontext)
 	 * mlx4_ib_vma_close().
 	 */
 	down_write(&owning_mm->mmap_sem);
+	if (!mmget_still_valid(owning_mm))
+		goto skip_mm;
 	for (i = 0; i < HW_BAR_COUNT; i++) {
 		vma = context->hw_bar_info[i].vma;
 		if (!vma)
@@ -1061,6 +1063,7 @@ static void mlx4_ib_disassociate_ucontext(struct ib_ucontext *ibcontext)
 		context->hw_bar_info[i].vma->vm_ops = NULL;
 	}
 
+skip_mm:
 	up_write(&owning_mm->mmap_sem);
 	mmput(owning_mm);
 	put_task_struct(owning_process);
-- 
Michal Hocko
SUSE Labs