On Tue, Sep 16, 2025 at 7:44 AM Yunseong Kim ysk@kzalloc.com wrote:
The 'sess->rpc_handle_list' XArray manages RPC handles within a ksmbd session. Access to this list is intended to be protected by 'sess->rpc_lock' (an rw_semaphore). However, the locking implementation was flawed, leading to potential race conditions.
In ksmbd_session_rpc_open(), the code incorrectly acquired only a read lock before calling xa_store() and xa_erase(). Since these operations modify the XArray structure, a write lock is required to ensure exclusive access and prevent data corruption from concurrent modifications.
Furthermore, ksmbd_session_rpc_method() accessed the list using xa_load() without holding any lock at all. This could lead to reading inconsistent data or a potential use-after-free if an entry is concurrently removed and the pointer is dereferenced.
Fix these issues by:
- Using down_write() and up_write() in ksmbd_session_rpc_open() to ensure exclusive access during XArray modification, and ensuring the lock is correctly released on error paths.
- Adding down_read() and up_read() in ksmbd_session_rpc_method() to safely protect the lookup.
Fixes: a1f46c99d9ea ("ksmbd: fix use-after-free in ksmbd_session_rpc_open") Fixes: b685757c7b08 ("ksmbd: Implements sess->rpc_handle_list as xarray") Cc: stable@vger.kernel.org Signed-off-by: Yunseong Kim ysk@kzalloc.com
Applied it to #ksmbd-for-next-next. Thanks!