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[104.194.93.216]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-12bedd4e4e3sm1716646c88.1.2026.04.02.01.39.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Apr 2026 01:39:20 -0700 (PDT) From: munan Huang To: linkinjeon@kernel.org, smfrench@gmail.com, senozhatsky@chromium.org, tom@talpey.com Cc: linux-cifs@vger.kernel.org, linux-kernel@vger.kernel.org, munan Huang , stable@vger.kernel.org Subject: [PATCH] ksmbd: fix use-after-free in __ksmbd_close_fd() lock cleanup Date: Thu, 2 Apr 2026 08:39:12 +0000 Message-Id: <20260402083912.457676-1-munanevil@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-cifs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In __ksmbd_close_fd(), when cleaning up byte-range locks on a durable file handle closed by the scavenger, the lock cleanup loop unconditionally dereferences fp->conn->llist_lock to remove each lock from the connection's list: list_for_each_entry_safe(smb_lock, tmp_lock, &fp->lock_list, flist) { spin_lock(&fp->conn->llist_lock); list_del(&smb_lock->clist); spin_unlock(&fp->conn->llist_lock); } However, when a client disconnects without SMB2 LOGOFF, ksmbd preserves durable file handles via session_fd_check(), which sets fp->conn to NULL and arms the durable scavenger timeout, but does not detach the byte-range locks from the dying connection's lock list. When the scavenger timeout expires, ksmbd_durable_scavenger() calls __ksmbd_close_fd(NULL, fp). At this point fp->conn is NULL and the original connection object has already been freed by ksmbd_conn_free(), so it would cause a use-after-free or NULL pointer dereference. Fix by checking fp->conn for NULL before accessing fp->conn->llist_lock in the lock cleanup loop. Fixes: c8efcc786146 ("ksmbd: add support for durable handles v1/v2") Cc: stable@vger.kernel.org Signed-off-by: munan Huang --- fs/smb/server/vfs_cache.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/fs/smb/server/vfs_cache.c b/fs/smb/server/vfs_cache.c index 168f2dd7e200..772a84d95fe3 100644 --- a/fs/smb/server/vfs_cache.c +++ b/fs/smb/server/vfs_cache.c @@ -463,9 +463,11 @@ static void __ksmbd_close_fd(struct ksmbd_file_table *ft, struct ksmbd_file *fp) * there are not accesses to fp->lock_list. */ list_for_each_entry_safe(smb_lock, tmp_lock, &fp->lock_list, flist) { - spin_lock(&fp->conn->llist_lock); - list_del(&smb_lock->clist); - spin_unlock(&fp->conn->llist_lock); + if (fp->conn) { + spin_lock(&fp->conn->llist_lock); + list_del(&smb_lock->clist); + spin_unlock(&fp->conn->llist_lock); + } list_del(&smb_lock->flist); locks_free_lock(smb_lock->fl); -- 2.34.1