[PATCH 5.10.y 1/4] block: split out operations on block special files

[Sasha Levin <sashal@kernel.org>]

From: Christoph Hellwig <hch@lst.de>

[ Upstream commit cd82cca7ebfe9c6c74a8e5b28382ba88177ba5f1 ]

Add a new block/fops.c for all the file and address_space operations
that provide the block special file support.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210907141303.1371844-2-hch@lst.de
[axboe: correct trailing whitespace while at it]
Signed-off-by: Jens Axboe <axboe@kernel.dk>

[ sashal: Reduced backport -- upstream cd82cca7ebfe9 touches 4 file(s), this
  backport carries 1. Not backported here:
  block/blk.h
  block/fops.c
  block/Makefile
  fs/block_dev.c
  This note is generated from the file lists only; see the resolution record
  for the reasoning. ]

Stable-dep-of: e78dcb1f7ec2 ("usb: gadget: f_fs: Fix Use-After-Free in AIO error path")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/usb/gadget/function/f_fs.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index fa3444e6b67d4..75a27d3e261aa 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -831,9 +831,15 @@ static void ffs_user_copy_worker(struct work_struct *work)
 	unsigned long flags;
 
 	if (io_data->read && ret > 0) {
-		kthread_use_mm(io_data->mm);
-		ret = ffs_copy_to_iter(io_data->buf, ret, &io_data->data);
-		kthread_unuse_mm(io_data->mm);
+		if (mmget_not_zero(io_data->mm)) {
+			kthread_use_mm(io_data->mm);
+			ret = ffs_copy_to_iter(io_data->buf, ret, &io_data->data);
+			kthread_unuse_mm(io_data->mm);
+			mmput(io_data->mm);
+		} else {
+			ret = -EFAULT;
+		}
+		mmdrop(io_data->mm);
 	}
 
 	io_data->kiocb->ki_complete(io_data->kiocb, ret, ret);
@@ -1210,16 +1216,20 @@ static ssize_t ffs_epfile_write_iter(struct kiocb *kiocb, struct iov_iter *from)
 
 	kiocb->private = p;
 
-	if (p->aio)
+	if (p->aio) {
+		mmgrab(p->mm);
 		kiocb_set_cancel_fn(kiocb, ffs_aio_cancel);
+	}
 
 	res = ffs_epfile_io(kiocb->ki_filp, p);
 	if (res == -EIOCBQUEUED)
 		return res;
-	if (p->aio)
+	if (p->aio) {
+		mmdrop(p->mm);
 		kfree(p);
-	else
+	} else {
 		*from = p->data;
+	}
 	return res;
 }
 
@@ -1256,14 +1266,17 @@ static ssize_t ffs_epfile_read_iter(struct kiocb *kiocb, struct iov_iter *to)
 
 	kiocb->private = p;
 
-	if (p->aio)
+	if (p->aio) {
+		mmgrab(p->mm);
 		kiocb_set_cancel_fn(kiocb, ffs_aio_cancel);
+	}
 
 	res = ffs_epfile_io(kiocb->ki_filp, p);
 	if (res == -EIOCBQUEUED)
 		return res;
 
 	if (p->aio) {
+		mmdrop(p->mm);
 		kfree(p->to_free);
 		kfree(p);
 	} else {
-- 
2.53.0