[PATCH V2 1/2] block/loop: fix use after free

[Shaohua Li]

From: Shaohua Li <s...@fb.com>

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 <s...@fb.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 3a35121..78c47c4 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 43d20d3..b0ba4a5 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;
-- 
2.9.5