[PATCH] misc: fastrpc: remove mmap entry before remote unmap

[Yousef Alhouseen <alhouseenyousef@gmail.com>]

FASTRPC_IOCTL_MUNMAP looked up a buffer and dropped fl->lock.

It only deleted the list entry after the remote unmap succeeded.

Two threads can therefore find the same entry and unmap it twice.

That can lead to a double list deletion and double free.

Detach the entry before invoking the DSP.

Put it back if the remote unmap fails.

Signed-off-by: Yousef Alhouseen <alhouseenyousef@gmail.com>
---
 drivers/misc/fastrpc.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index ba4ade874..6a5239b1c 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -1902,7 +1902,8 @@ static int fastrpc_req_munmap_impl(struct fastrpc_user *fl, struct fastrpc_buf *
 	if (!err) {
 		dev_dbg(dev, "unmmap\tpt 0x%09lx OK\n", buf->raddr);
 		spin_lock(&fl->lock);
-		list_del(&buf->node);
+		if (!list_empty(&buf->node))
+			list_del_init(&buf->node);
 		spin_unlock(&fl->lock);
 		fastrpc_buf_free(buf);
 	} else {
@@ -1917,6 +1918,7 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
 	struct fastrpc_buf *buf = NULL, *iter, *b;
 	struct fastrpc_req_munmap req;
 	struct device *dev = fl->sctx->dev;
+	int err;
 
 	if (copy_from_user(&req, argp, sizeof(req)))
 		return -EFAULT;
@@ -1925,6 +1927,7 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
 	list_for_each_entry_safe(iter, b, &fl->mmaps, node) {
 		if ((iter->raddr == req.vaddrout) && (iter->size == req.size)) {
 			buf = iter;
+			list_del_init(&buf->node);
 			break;
 		}
 	}
@@ -1936,7 +1939,14 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
 		return -EINVAL;
 	}
 
-	return fastrpc_req_munmap_impl(fl, buf);
+	err = fastrpc_req_munmap_impl(fl, buf);
+	if (err) {
+		spin_lock(&fl->lock);
+		list_add_tail(&buf->node, &fl->mmaps);
+		spin_unlock(&fl->lock);
+	}
+
+	return err;
 }
 
 static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
-- 
2.54.0