[PATCH 7.1 191/271] misc: fastrpc: take fl->lock when moving mmaps on interrupted invoke

7.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Junrui Luo <[email protected]>

commit b85a0e91d7d6cd06a53c881a46f749cfcef416a2 upstream.

When an invoke is interrupted by a signal,
wait_for_completion_interruptible() returns -ERESTARTSYS and
fastrpc_internal_invoke() moves every buffer from fl->mmaps onto
cctx->invoke_interrupted_mmaps. This list_del()/list_add_tail() walk
runs without holding fl->lock, the lock that serialises fl->mmaps in
fastrpc_req_mmap() and fastrpc_req_munmap() everywhere else.

Take fl->lock around the move, matching every other fl->mmaps accessor.

Fixes: 76e8e4ace1ed ("misc: fastrpc: Safekeep mmaps on interrupted invoke")
Reported-by: Yuhao Jiang <[email protected]>
Cc: [email protected]
Signed-off-by: Junrui Luo <[email protected]>
Reviewed-by: Dmitry Baryshkov <[email protected]>
Signed-off-by: Srinivas Kandagatla <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/misc/fastrpc.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -1305,10 +1305,12 @@ bail:
 	}
 
 	if (err == -ERESTARTSYS) {
+		spin_lock(&fl->lock);
 		list_for_each_entry_safe(buf, b, &fl->mmaps, node) {
 			list_del(&buf->node);
 			list_add_tail(&buf->node, &fl->cctx->invoke_interrupted_mmaps);
 		}
+		spin_unlock(&fl->lock);
 	}
 
 	if (err)