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Fri, 01 May 2026 15:51:57 -0700 (PDT) From: Kai Aizen To: stable@vger.kernel.org Cc: gregkh@linuxfoundation.org, linkinjeon@kernel.org, linux-cifs@vger.kernel.org, samba-technical@lists.samba.org Subject: [PATCH 5.15.y] ksmbd: add chann_lock to protect ksmbd_chann_list xarray Date: Sat, 2 May 2026 01:51:52 +0300 Message-ID: <20260501225152.90136-3-kai.aizen.dev@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260501225152.90136-1-kai.aizen.dev@gmail.com> References: <20260501225152.90136-1-kai.aizen.dev@gmail.com> Precedence: bulk X-Mailing-List: linux-cifs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Namjae Jeon [ Upstream commit 4f3a06cc57976cafa8c6f716646be6c79a99e485 ] ksmbd_chann_list xarray lacks synchronization, allowing use-after-free in multi-channel sessions (between lookup_chann_list() and ksmbd_chann_del). Adds rw_semaphore chann_lock to struct ksmbd_session and protects all xa_load/xa_store/xa_erase accesses. Backport notes for linux-5.15.y: - 5.15 still uses fs/ksmbd/ paths (the smb client/server consolidation landed in 6.1). - struct ksmbd_session does not yet have rpc_lock; init_rwsem for chann_lock is added directly after the refcnt initialisation. - Function bodies for free_channel_list, ksmbd_chann_del, lookup_chann_list, and the two xa_store sites in ntlm_authenticate / krb5_authenticate are byte-identical to mainline at the time of the fix. CVE: CVE-2026-23226 Cc: stable@vger.kernel.org # 5.15.y Reported-by: Igor Stepansky Signed-off-by: Namjae Jeon Signed-off-by: Steve French [backport for linux-5.15.y, verified 2026-05-01] --- fs/ksmbd/mgmt/user_session.c | 5 +++++ fs/ksmbd/mgmt/user_session.h | 1 + fs/ksmbd/smb2pdu.c | 12 +++++++++++- 3 files changed, 17 insertions(+), 1 deletion(-) diff --git a/fs/ksmbd/mgmt/user_session.c b/fs/ksmbd/mgmt/user_session.c --- a/fs/ksmbd/mgmt/user_session.c +++ b/fs/ksmbd/mgmt/user_session.c @@ -30,12 +30,14 @@ static void free_channel_list(struct ksmbd_session *sess) struct channel *chann; unsigned long index; + down_write(&sess->chann_lock); xa_for_each(&sess->ksmbd_chann_list, index, chann) { xa_erase(&sess->ksmbd_chann_list, index); kfree(chann); } xa_destroy(&sess->ksmbd_chann_list); + up_write(&sess->chann_lock); } static void __session_rpc_close(struct ksmbd_session *sess, @@ -201,7 +203,9 @@ static int ksmbd_chann_del(struct ksmbd_conn *conn, struct ksmbd_session *sess) { struct channel *chann; + down_write(&sess->chann_lock); chann = xa_erase(&sess->ksmbd_chann_list, (long)conn); + up_write(&sess->chann_lock); if (!chann) return -ENOENT; @@ -395,6 +399,7 @@ static struct ksmbd_session *__session_create(int protocol) sess->sequence_number = 1; rwlock_init(&sess->tree_conns_lock); atomic_set(&sess->refcnt, 1); + init_rwsem(&sess->chann_lock); ret = __init_smb2_session(sess); if (ret) diff --git a/fs/ksmbd/mgmt/user_session.h b/fs/ksmbd/mgmt/user_session.h --- a/fs/ksmbd/mgmt/user_session.h +++ b/fs/ksmbd/mgmt/user_session.h @@ -48,6 +48,7 @@ struct ksmbd_session { char sess_key[CIFS_KEY_SIZE]; struct hlist_node hlist; + struct rw_semaphore chann_lock; struct xarray ksmbd_chann_list; struct xarray tree_conns; struct ida tree_conn_ida; diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c --- a/fs/ksmbd/smb2pdu.c +++ b/fs/ksmbd/smb2pdu.c @@ -78,7 +78,13 @@ static inline bool check_session_id(struct ksmbd_conn *conn, u64 id) struct channel *lookup_chann_list(struct ksmbd_session *sess, struct ksmbd_conn *conn) { - return xa_load(&sess->ksmbd_chann_list, (long)conn); + struct channel *chann; + + down_read(&sess->chann_lock); + chann = xa_load(&sess->ksmbd_chann_list, (long)conn); + up_read(&sess->chann_lock); + + return chann; } /** @@ -1570,7 +1576,9 @@ static int ntlm_authenticate(struct ksmbd_work *work, return -ENOMEM; chann->conn = conn; + down_write(&sess->chann_lock); xa_store(&sess->ksmbd_chann_list, (long)conn, chann, GFP_KERNEL); + up_write(&sess->chann_lock); } } @@ -1667,7 +1675,9 @@ static int krb5_authenticate(struct ksmbd_work *work, return -ENOMEM; chann->conn = conn; + down_write(&sess->chann_lock); xa_store(&sess->ksmbd_chann_list, (long)conn, chann, GFP_KERNEL); + up_write(&sess->chann_lock); } } -- 2.43.0