From 61a0890cb95afec5c8a2f4a879de2b6220984ef1 Mon Sep 17 00:00:00 2001
From: Ola Jeppsson <ola@snap.com>
Date: Thu, 24 Nov 2022 17:49:41 +0000
Subject: [PATCH] misc: fastrpc: Fix use-after-free race condition for maps
commit 96b328d119eca7563c1edcc4e1039a62e6370ecb upstream.
It is possible that in between calling fastrpc_map_get() until
map->fl->lock is taken in fastrpc_free_map(), another thread can call
fastrpc_map_lookup() and get a reference to a map that is about to be
deleted.
Rewrite fastrpc_map_get() to only increase the reference count of a map
if it's non-zero. Propagate this to callers so they can know if a map is
about to be deleted.
Fixes this warning:
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 5 PID: 10100 at lib/refcount.c:25 refcount_warn_saturate
...
Call trace:
refcount_warn_saturate
[fastrpc_map_get inlined]
[fastrpc_map_lookup inlined]
fastrpc_map_create
fastrpc_internal_invoke
fastrpc_device_ioctl
__arm64_sys_ioctl
invoke_syscall
Fixes: c68cfb718c8f ("misc: fastrpc: Add support for context Invoke method")
Cc: stable <stable@kernel.org>
Signed-off-by: Ola Jeppsson <ola@snap.com>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20221124174941.418450-4-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/misc/fastrpc.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index f2f422ed0020d..55e42ccaef436 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -263,10 +263,12 @@ static void fastrpc_map_put(struct fastrpc_map *map)
kref_put(&map->refcount, fastrpc_free_map);
}
-static void fastrpc_map_get(struct fastrpc_map *map)
+static int fastrpc_map_get(struct fastrpc_map *map)
{
- if (map)
- kref_get(&map->refcount);
+ if (!map)
+ return -ENOENT;
+
+ return kref_get_unless_zero(&map->refcount) ? 0 : -ENOENT;
}
static int fastrpc_map_find(struct fastrpc_user *fl, int fd,
--
2.30.2