From e7188199eff46a636f3436356f0aae039be6dd66 Mon Sep 17 00:00:00 2001 From: Namjae Jeon Date: Wed, 22 Jul 2026 10:04:19 +0900 Subject: [PATCH 1/3] ksmbd: fix use-after-free in __close_file_table_ids() A ksmbd_file can remain alive after logical close while another session holds a temporary reference obtained through ksmbd_lookup_fd_inode(). ksmbd_close_fd() currently marks the file closed and drops the idr-owned reference, but leaves the pointer published in the closing session's idr until the final reference is dropped. If the foreign holder performs the final ksmbd_fd_put(), __put_fd_final() supplies the foreign session's file table to __ksmbd_close_fd(). The object is then freed without being removed from its owner's idr, and the owner session later dereferences the stale pointer during file-table teardown. Remove the volatile id from the owner's idr while ksmbd_close_fd() still holds that table's lock, and clear volatile_id before dropping the idr-owned reference. A later foreign final put then only performs physical destruction and cannot remove the object from the wrong table. Fixes: 8510a043d334 ("ksmbd: increment reference count of parent fp") Reported-by: Yunseong Kim Signed-off-by: Namjae Jeon Signed-off-by: Steve French --- fs/smb/server/vfs_cache.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/smb/server/vfs_cache.c b/fs/smb/server/vfs_cache.c index d95c405eab11..a141025581af 100644 --- a/fs/smb/server/vfs_cache.c +++ b/fs/smb/server/vfs_cache.c @@ -697,6 +697,8 @@ int ksmbd_close_fd(struct ksmbd_work *work, u64 id) fp = NULL; else { fp->f_state = FP_CLOSED; + idr_remove(ft->idr, id); + fp->volatile_id = KSMBD_NO_FID; closed = true; if (!atomic_dec_and_test(&fp->refcount)) fp = NULL; From cb469993b3a61a72653770856d37af616d72d05f Mon Sep 17 00:00:00 2001 From: Namjae Jeon Date: Thu, 23 Jul 2026 23:07:14 +0900 Subject: [PATCH 2/3] ksmbd: reject repeated SMB2 NEGOTIATE requests Unauthenticated client can send multiple successful SMB2 NEGOTIATE requests on one connection before SESSION_SETUP. While the connection is in KSMBD_SESS_NEED_SETUP, smb2_handle_negotiate() accepts another SMB3.1.1 NEGOTIATE and overwrites conn->preauth_info with a new allocation. Only the final allocation is freed when the connection is released, leaking one object for every additional successful request. A repeated SMB2 NEGOTIATE after a dialect has been selected is a protocol violation. MS-SMB2 section 3.3.5.4 requires the server to disconnect without replying in this case. Set the connection exiting when rejecting the request, in addition to suppressing the response. Reject SMB2 NEGOTIATE unless the connection is new or is waiting for the SMB2 NEGOTIATE that follows an SMB1 multi-protocol negotiate. Serialize both SMB1 and SMB2 negotiation paths under conn->srv_mutex, since they update connection-wide dialect and negotiation state. Move the locking contract to ksmbd_smb_negotiate_common(), where the state and dialect are selected, and add ksmbd_conn_new() for consistent state access. Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3") Cc: stable@vger.kernel.org Reported-by: Runa Takemoto Signed-off-by: Namjae Jeon Signed-off-by: Steve French --- fs/smb/server/connection.h | 5 +++++ fs/smb/server/smb2pdu.c | 10 ++-------- fs/smb/server/smb_common.c | 37 ++++++++++++++++++++++++++++++------- 3 files changed, 37 insertions(+), 15 deletions(-) diff --git a/fs/smb/server/connection.h b/fs/smb/server/connection.h index ec75633b7da0..2a194ee36fb4 100644 --- a/fs/smb/server/connection.h +++ b/fs/smb/server/connection.h @@ -200,6 +200,11 @@ void ksmbd_conn_r_count_dec(struct ksmbd_conn *conn); * This is a hack. We will move status to a proper place once we land * a multi-sessions support. */ +static inline bool ksmbd_conn_new(struct ksmbd_conn *conn) +{ + return READ_ONCE(conn->status) == KSMBD_SESS_NEW; +} + static inline bool ksmbd_conn_good(struct ksmbd_conn *conn) { return READ_ONCE(conn->status) == KSMBD_SESS_GOOD; diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c index c1ba5e01aa7f..404a4203f7da 100644 --- a/fs/smb/server/smb2pdu.c +++ b/fs/smb/server/smb2pdu.c @@ -1325,6 +1325,8 @@ static __le32 deassemble_neg_contexts(struct ksmbd_conn *conn, * smb2_handle_negotiate() - handler for smb2 negotiate command * @work: smb work containing smb request buffer * + * The caller holds conn->srv_mutex. + * * Return: 0 */ int smb2_handle_negotiate(struct ksmbd_work *work) @@ -1338,13 +1340,6 @@ int smb2_handle_negotiate(struct ksmbd_work *work) ksmbd_debug(SMB, "Received negotiate request\n"); conn->need_neg = false; - if (ksmbd_conn_good(conn)) { - pr_err("conn->tcp_status is already in CifsGood State\n"); - work->send_no_response = 1; - return rc; - } - - ksmbd_conn_lock(conn); smb2_buf_len = get_rfc1002_len(work->request_buf); smb2_neg_size = offsetof(struct smb2_negotiate_req, Dialects); if (smb2_neg_size > smb2_buf_len) { @@ -1495,7 +1490,6 @@ int smb2_handle_negotiate(struct ksmbd_work *work) ksmbd_conn_set_need_setup(conn); err_out: - ksmbd_conn_unlock(conn); if (rc) rsp->hdr.Status = STATUS_INSUFFICIENT_RESOURCES; diff --git a/fs/smb/server/smb_common.c b/fs/smb/server/smb_common.c index 7de73223189a..080fbc9eb470 100644 --- a/fs/smb/server/smb_common.c +++ b/fs/smb/server/smb_common.c @@ -608,23 +608,46 @@ int ksmbd_smb_negotiate_common(struct ksmbd_work *work, unsigned int command) struct ksmbd_conn *conn = work->conn; int ret; - conn->dialect = - ksmbd_negotiate_smb_dialect(work->request_buf); - ksmbd_debug(SMB, "conn->dialect 0x%x\n", conn->dialect); - if (command == SMB2_NEGOTIATE_HE) { + /* + * An SMB2 NEGOTIATE is valid for a new connection, or after an + * SMB1 multi-protocol negotiate has selected SMB2. Do not allow + * a second SMB2 NEGOTIATE to replace connection-wide state + * while a session setup is pending. KSMBD_SESS_NEED_RECONNECT + * is a transient session state and does not restart transport + * negotiation. + */ + ksmbd_conn_lock(conn); + if (!ksmbd_conn_new(conn) && + !ksmbd_conn_need_negotiate(conn)) { + work->send_no_response = 1; + ksmbd_conn_set_exiting(conn); + ksmbd_conn_unlock(conn); + return 0; + } + + conn->dialect = + ksmbd_negotiate_smb_dialect(work->request_buf); + ksmbd_debug(SMB, "conn->dialect 0x%x\n", conn->dialect); ret = smb2_handle_negotiate(work); + ksmbd_conn_unlock(conn); return ret; } if (command == SMB_COM_NEGOTIATE) { + ksmbd_conn_lock(conn); + conn->dialect = + ksmbd_negotiate_smb_dialect(work->request_buf); + ksmbd_debug(SMB, "conn->dialect 0x%x\n", conn->dialect); if (__smb2_negotiate(conn)) { init_smb3_11_server(conn); - init_smb2_neg_rsp(work); + ret = init_smb2_neg_rsp(work); ksmbd_debug(SMB, "Upgrade to SMB2 negotiation\n"); - return 0; + } else { + ret = smb_handle_negotiate(work); } - return smb_handle_negotiate(work); + ksmbd_conn_unlock(conn); + return ret; } pr_err("Unknown SMB negotiation command: %u\n", command); From e8bb506e6ef749ac0336f3e579d8d02396b7d832 Mon Sep 17 00:00:00 2001 From: Namjae Jeon Date: Mon, 20 Jul 2026 10:32:01 +0900 Subject: [PATCH 3/3] ksmbd: use memcmp() to compare ClientGUIDs ClientGUID is a fixed-size binary value and can contain embedded NUL bytes. strncmp() stops comparing at the first NUL byte, so different ClientGUID values can incorrectly be treated as equal. Use memcmp() in SMB3 multichannel session binding and FSCTL_VALIDATE_NEGOTIATE_INFO to compare all SMB2_CLIENT_GUID_SIZE bytes. Fixes: f5a544e3bab7 ("ksmbd: add support for SMB3 multichannel") Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3") Reported-by: Samu Suggested-by: Samu Signed-off-by: Namjae Jeon Signed-off-by: Steve French --- fs/smb/server/smb2pdu.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c index 404a4203f7da..76f63f9adc72 100644 --- a/fs/smb/server/smb2pdu.c +++ b/fs/smb/server/smb2pdu.c @@ -1969,7 +1969,7 @@ int smb2_sess_setup(struct ksmbd_work *work) goto out_err; } - if (strncmp(conn->ClientGUID, sess->ClientGUID, + if (memcmp(conn->ClientGUID, sess->ClientGUID, SMB2_CLIENT_GUID_SIZE)) { rc = -ENOENT; goto out_err; @@ -8690,7 +8690,7 @@ static int fsctl_validate_negotiate_info(struct ksmbd_conn *conn, goto err_out; } - if (strncmp(neg_req->Guid, conn->ClientGUID, SMB2_CLIENT_GUID_SIZE)) { + if (memcmp(neg_req->Guid, conn->ClientGUID, SMB2_CLIENT_GUID_SIZE)) { ret = -EINVAL; goto err_out; }