From: Shaohua Li <shli@fb.com>
Date: Fri, 1 Sep 2017 11:15:17 -0700
Subject: [PATCH] block/loop: fix use after free
Git-commit: 92d773324b7edbd36bf0c28c1e0157763aeccc92
Patch-mainline: v4.14-rc1
References: bsc#1104967,FATE#325924

lo_rw_aio->call_read_iter->
1       aops->direct_IO
2       iov_iter_revert
lo_rw_aio_complete could happen between 1 and 2, the bio and bvec could
be freed before 2, which accesses bvec.

Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 drivers/block/loop.c | 16 +++++++++++++---
 drivers/block/loop.h |  5 ++++-
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 3a35121f8a6f..78c47c4b584d 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -463,14 +463,21 @@ static void lo_complete_rq(struct request *rq)
 	blk_mq_end_request(rq, cmd->ret < 0 ? BLK_STS_IOERR : BLK_STS_OK);
 }
 
+static void lo_rw_aio_do_completion(struct loop_cmd *cmd)
+{
+	if (!atomic_dec_and_test(&cmd->ref))
+		return;
+	kfree(cmd->bvec);
+	cmd->bvec = NULL;
+	blk_mq_complete_request(cmd->rq);
+}
+
 static void lo_rw_aio_complete(struct kiocb *iocb, long ret, long ret2)
 {
 	struct loop_cmd *cmd = container_of(iocb, struct loop_cmd, iocb);
 
-	kfree(cmd->bvec);
-	cmd->bvec = NULL;
 	cmd->ret = ret;
-	blk_mq_complete_request(cmd->rq);
+	lo_rw_aio_do_completion(cmd);
 }
 
 static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
@@ -518,6 +525,7 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
 		bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
 		segments = bio_segments(bio);
 	}
+	atomic_set(&cmd->ref, 2);
 
 	iov_iter_bvec(&iter, ITER_BVEC | rw, bvec,
 		      segments, blk_rq_bytes(rq));
@@ -533,6 +541,8 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
 	else
 		ret = call_read_iter(file, &cmd->iocb, &iter);
 
+	lo_rw_aio_do_completion(cmd);
+
 	if (ret != -EIOCBQUEUED)
 		cmd->iocb.ki_complete(&cmd->iocb, ret, 0);
 	return 0;
diff --git a/drivers/block/loop.h b/drivers/block/loop.h
index 43d20d37b79a..b0ba4a5951c4 100644
--- a/drivers/block/loop.h
+++ b/drivers/block/loop.h
@@ -68,7 +68,10 @@ struct loop_cmd {
 	struct kthread_work work;
 	struct request *rq;
 	struct list_head list;
-	bool use_aio;           /* use AIO interface to handle I/O */
+	union {
+		bool use_aio; /* use AIO interface to handle I/O */
+		atomic_t ref; /* only for aio */
+	};
 	long ret;
 	struct kiocb iocb;
 	struct bio_vec *bvec;
-- 
2.16.4