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: abead65aaaf5 ("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>

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 268c3f602c2e4670c16c475c3defd943f2bdd280..19840ad58a5fbfd0b68c41e851d87dcce7ccfec3 100644 (file)
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -234,10 +234,12 @@ 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,