[PATCH 5.10 17/63] io_uring: dont assume mm is constant across submits

Greg Kroah-Hartman
2021-01-04T16:07:33Z

From: Jens Axboe <axboe@kernel.dk>

commit 77788775c7132a8d93c6930ab1bd84fc743c7cb7 upstream.

If we COW the identity, we assume that ->mm never changes. But this
isn't true of multiple processes end up sharing the ring. Hence treat
id->mm like like any other process compontent when it comes to the
identity mapping. This is pretty trivial, just moving the existing grab
into io_grab_identity(), and including a check for the match.

Cc: stable@vger.kernel.org # 5.10
Fixes: 1e6fa5216a0e ("io_uring: COW io_identity on mismatch")
Reported-by: Christian Brauner <christian.brauner@ubuntu.com>:
Tested-by: Christian Brauner <christian.brauner@ubuntu.com>:
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/io_uring.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1369,6 +1369,13 @@ static bool io_grab_identity(struct io_k
spin_unlock_irq(&ctx->inflight_lock);
req->work.flags |= IO_WQ_WORK_FILES;
}
+ if (!(req->work.flags & IO_WQ_WORK_MM) &&
+ (def->work_flags & IO_WQ_WORK_MM)) {
+ if (id->mm != current->mm)
+ return false;
+ mmgrab(id->mm);
+ req->work.flags |= IO_WQ_WORK_MM;
+ }

return true;
}
@@ -1393,13 +1400,6 @@ static void io_prep_async_work(struct io
req->work.flags |= IO_WQ_WORK_UNBOUND;
}

- /* ->mm can never change on us */
- if (!(req->work.flags & IO_WQ_WORK_MM) &&
- (def->work_flags & IO_WQ_WORK_MM)) {
- mmgrab(id->mm);
- req->work.flags |= IO_WQ_WORK_MM;
- }
-
/* if we fail grabbing identity, we must COW, regrab, and retry */
if (io_grab_identity(req))
return;