[PATCH 5.8 15/16] io_uring: fix missing ->mm on exit

Greg Kroah-Hartman
2020-08-26T12:06:36Z

From: Pavel Begunkov <asml.silence@gmail.com>

Upstream commits:

8eb06d7e8dd85 ("io_uring: fix missing ->mm on exit")
cbcf72148da4a ("io_uring: return locked and pinned page accounting")

do_exit() first drops current->mm and then runs task_work, from where
io_sq_thread_acquire_mm() would try to set mm for a user dying process.

[ 208.004249] WARNING: CPU: 2 PID: 1854 at
kernel/kthread.c:1238 kthread_use_mm+0x244/0x270
[ 208.004287] kthread_use_mm+0x244/0x270
[ 208.004288] io_sq_thread_acquire_mm.part.0+0x54/0x80
[ 208.004290] io_async_task_func+0x258/0x2ac
[ 208.004291] task_work_run+0xc8/0x210
[ 208.004294] do_exit+0x1b8/0x430
[ 208.004295] do_group_exit+0x44/0xac
[ 208.004296] get_signal+0x164/0x69c
[ 208.004298] do_signal+0x94/0x1d0
[ 208.004299] do_notify_resume+0x18c/0x340
[ 208.004300] work_pending+0x8/0x3d4

Reported-by: Roman Gershman <romange@gmail.com>
Tested-by: Roman Gershman <romange@gmail.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/io_uring.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4363,7 +4363,8 @@ static int io_sq_thread_acquire_mm(struc
struct io_kiocb *req)
{
if (io_op_defs[req->opcode].needs_mm && !current->mm) {
- if (unlikely(!mmget_not_zero(ctx->sqo_mm)))
+ if (unlikely(!(ctx->flags & IORING_SETUP_SQPOLL) ||
+ !mmget_not_zero(ctx->sqo_mm)))
return -EFAULT;
kthread_use_mm(ctx->sqo_mm);
}