kernel/linux.git/fs/smb/server/server.c, branch v6.12.98

ksmbd: centralize ksmbd_conn final release to plug transport leak

2026-07-24T14:11:50+00:00

[ Upstream commit b1f1e80620deb49daf63c2e677046599b693dc1f ] ksmbd_conn_free() is one of four sites that can observe the last refcount drop of a struct ksmbd_conn. The other three fs/smb/server/connection.c ksmbd_conn_r_count_dec() fs/smb/server/oplock.c __free_opinfo() fs/smb/server/vfs_cache.c session_fd_check() end the conn with a bare kfree(), skipping ida_destroy(&conn->async_ida) and conn->transport->ops->free_transport(conn->transport). Whenever one of them is the last putter, the embedded async_ida and the entire transport struct leak -- for TCP, that is also the struct socket and the kvec iov. __free_opinfo() being a final putter is not theoretical. opinfo_put() queues the callback via call_rcu(&opinfo->rcu, free_opinfo_rcu), so ksmbd_server_terminate_conn() can deposit N opinfo releases in RCU and have ksmbd_conn_free() run in the handler thread before any of them fire. ksmbd_conn_free() then observes refcnt > 0 and short-circuits; the last RCU-delivered __free_opinfo() falls onto its bare kfree(conn) branch and the transport is lost. A/B validation in a QEMU/virtme guest, mounting //127.0.0.1/testshare: each iteration holds 8 files open via sleep processes, force-closes TCP with "ss -K sport = :445", kills the holders, lazy-umounts; repeated 10 times, then ksmbd shutdown and kmemleak scan. state conn_alloc conn_free tcp_free opi_rcu kmemleak ---------- ---------- --------- -------- ------- -------- pre-patch 20 20 10 160 7 with patch 20 20 20 160 0 Pre-patch conn_free=20 with tcp_free=10 directly demonstrates the bare-kfree paths skipping transport cleanup; kmemleak backtraces point into struct tcp_transport / iov. With this patch tcp_free matches conn_free at 20/20 and kmemleak is clean. Move the per-struct final release into __ksmbd_conn_release_work() and route the three bare-kfree final-put sites through a new ksmbd_conn_put(). Those sites now pair ida_destroy() and free_transport() with kfree(conn) regardless of which holder happens to release the last reference. stop_sessions() only triggers the transport shutdown and does not itself drop the last conn reference, so it is unaffected. The centralized release reaches sock_release() -> tcp_close() -> lock_sock_nested() (might_sleep) from every final putter, including __free_opinfo() invoked from an RCU softirq callback, which trips CONFIG_DEBUG_ATOMIC_SLEEP. Defer the release to a dedicated ksmbd_conn_wq workqueue so ksmbd_conn_put() is safe from any non-sleeping context. Make ksmbd_file own a strong connection reference while fp->conn is non-NULL so durable-preserve and final-close paths cannot dereference a stale connection. ksmbd_open_fd() and ksmbd_reopen_durable_fd() take the reference via ksmbd_conn_get() (the latter also reorders the fp->conn / fp->tcon assignments before __open_id() so the published fp is never observed with fp->conn == NULL); session_fd_check() and __ksmbd_close_fd() drop it via ksmbd_conn_put(). With that invariant, session_fd_check() can take a local conn pointer once and use it across the m_op_list and lock_list iterations even though op->conn puts may otherwise drop the last reference. At module exit the workqueue is flushed and destroyed after rcu_barrier(), so any release queued by a trailing RCU callback is drained before the inode hash and module text go away. Fixes: ee426bfb9d09 ("ksmbd: add refcnt to ksmbd_conn struct") Signed-off-by: DaeMyung Kang Acked-by: Namjae Jeon Signed-off-by: Steve French Stable-dep-of: c1016dd1d8b2 ("ksmbd: track the connection owning a byte-range lock") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

ksmbd: fix infinite loop caused by next_smb2_rcv_hdr_off reset in error paths

2026-02-16T09:18:43+00:00

commit 010eb01ce23b34b50531448b0da391c7f05a72af upstream. The problem occurs when a signed request fails smb2 signature verification check. In __process_request(), if check_sign_req() returns an error, set_smb2_rsp_status(work, STATUS_ACCESS_DENIED) is called. set_smb2_rsp_status() set work->next_smb2_rcv_hdr_off as zero. By resetting next_smb2_rcv_hdr_off to zero, the pointer to the next command in the chain is lost. Consequently, is_chained_smb2_message() continues to point to the same request header instead of advancing. If the header's NextCommand field is non-zero, the function returns true, causing __handle_ksmbd_work() to repeatedly process the same failed request in an infinite loop. This results in the kernel log being flooded with "bad smb2 signature" messages and high CPU usage. This patch fixes the issue by changing the return value from SERVER_HANDLER_CONTINUE to SERVER_HANDLER_ABORT. This ensures that the processing loop terminates immediately rather than attempting to continue from an invalidated offset. Reported-by: tianshuo han Cc: stable@vger.kernel.org Signed-off-by: Namjae Jeon Signed-off-by: Steve French Signed-off-by: Greg Kroah-Hartman

ksmbd: use __GFP_RETRY_MAYFAIL

2025-05-02T05:58:56+00:00

[ Upstream commit 0066f623bce8f98b69b752ee03d46a5047c281b8 ] Prefer to report ENOMEM rather than incur the oom for allocations in ksmbd. __GFP_NORETRY could not achieve that, It would fail the allocations just too easily. __GFP_RETRY_MAYFAIL will keep retrying the allocation until there is no more progress and fail the allocation instead go OOM and let the caller to deal with it. Signed-off-by: Namjae Jeon Signed-off-by: Steve French Stable-dep-of: 21a4e47578d4 ("ksmbd: fix use-after-free in __smb2_lease_break_noti()") Signed-off-by: Sasha Levin

ksmbd: prevent connection release during oplock break notification

2025-03-22T19:54:24+00:00

commit 3aa660c059240e0c795217182cf7df32909dd917 upstream. ksmbd_work could be freed when after connection release. Increment r_count of ksmbd_conn to indicate that requests are not finished yet and to not release the connection. Cc: stable@vger.kernel.org Reported-by: Norbert Szetei Tested-by: Norbert Szetei Signed-off-by: Namjae Jeon Signed-off-by: Steve French Signed-off-by: Greg Kroah-Hartman

ksmbd: fix broken transfers when exceeding max simultaneous operations

2024-12-27T13:02:03+00:00

[ Upstream commit 43fb7bce8866e793275c4f9f25af6a37745f3416 ] Since commit 0a77d947f599 ("ksmbd: check outstanding simultaneous SMB operations"), ksmbd enforces a maximum number of simultaneous operations for a connection. The problem is that reaching the limit causes ksmbd to close the socket, and the client has no indication that it should have slowed down. This behaviour can be reproduced by setting "smb2 max credits = 128" (or lower), and transferring a large file (25GB). smbclient fails as below: $ smbclient //192.168.1.254/testshare -U user%pass smb: \> put file.bin cli_push returned NT_STATUS_USER_SESSION_DELETED putting file file.bin as \file.bin smb2cli_req_compound_submit: Insufficient credits. 0 available, 1 needed NT_STATUS_INTERNAL_ERROR closing remote file \file.bin smb: \> smb2cli_req_compound_submit: Insufficient credits. 0 available, 1 needed Windows clients fail with 0x8007003b (with smaller files even). Fix this by delaying reading from the socket until there's room to allocate a request. This effectively applies backpressure on the client, so the transfer completes, albeit at a slower rate. Fixes: 0a77d947f599 ("ksmbd: check outstanding simultaneous SMB operations") Signed-off-by: Marios Makassikis Signed-off-by: Namjae Jeon Signed-off-by: Steve French Signed-off-by: Sasha Levin

ksmbd: fix racy issue from session lookup and expire

2024-12-19T17:12:58+00:00

commit b95629435b84b9ecc0c765995204a4d8a913ed52 upstream. Increment the session reference count within the lock for lookup to avoid racy issue with session expire. Cc: stable@vger.kernel.org Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-25737 Signed-off-by: Namjae Jeon Signed-off-by: Steve French Signed-off-by: Greg Kroah-Hartman

ksmbd: fix use-after-free in SMB request handling

2024-12-05T13:02:52+00:00

commit 9a8c5d89d327ff58e9b2517f8a6afb4181d32c6e upstream. A race condition exists between SMB request handling in `ksmbd_conn_handler_loop()` and the freeing of `ksmbd_conn` in the workqueue handler `handle_ksmbd_work()`. This leads to a UAF. - KASAN: slab-use-after-free Read in handle_ksmbd_work - KASAN: slab-use-after-free in rtlock_slowlock_locked This race condition arises as follows: - `ksmbd_conn_handler_loop()` waits for `conn->r_count` to reach zero: `wait_event(conn->r_count_q, atomic_read(&conn->r_count) == 0);` - Meanwhile, `handle_ksmbd_work()` decrements `conn->r_count` using `atomic_dec_return(&conn->r_count)`, and if it reaches zero, calls `ksmbd_conn_free()`, which frees `conn`. - However, after `handle_ksmbd_work()` decrements `conn->r_count`, it may still access `conn->r_count_q` in the following line: `waitqueue_active(&conn->r_count_q)` or `wake_up(&conn->r_count_q)` This results in a UAF, as `conn` has already been freed. The discovery of this UAF can be referenced in the following PR for syzkaller's support for SMB requests. Link: https://github.com/google/syzkaller/pull/5524 Fixes: ee426bfb9d09 ("ksmbd: add refcnt to ksmbd_conn struct") Cc: linux-cifs@vger.kernel.org Cc: stable@vger.kernel.org # v6.6.55+, v6.10.14+, v6.11.3+ Cc: syzkaller@googlegroups.com Signed-off-by: Yunseong Kim Acked-by: Namjae Jeon Signed-off-by: Steve French Signed-off-by: Greg Kroah-Hartman

ksmbd: check outstanding simultaneous SMB operations

2024-11-05T00:26:38+00:00

If Client send simultaneous SMB operations to ksmbd, It exhausts too much memory through the "ksmbd_work_cache”. It will cause OOM issue. ksmbd has a credit mechanism but it can't handle this problem. This patch add the check if it exceeds max credits to prevent this problem by assuming that one smb request consumes at least one credit. Cc: stable@vger.kernel.org # v5.15+ Reported-by: Norbert Szetei Tested-by: Norbert Szetei Signed-off-by: Namjae Jeon Signed-off-by: Steve French

ksmbd: fix slab-use-after-free in smb3_preauth_hash_rsp

2024-11-05T00:26:37+00:00

ksmbd_user_session_put should be called under smb3_preauth_hash_rsp(). It will avoid freeing session before calling smb3_preauth_hash_rsp(). Cc: stable@vger.kernel.org # v5.15+ Reported-by: Norbert Szetei Tested-by: Norbert Szetei Signed-off-by: Namjae Jeon Signed-off-by: Steve French

ksmbd: fix user-after-free from session log off

2024-10-10T02:23:17+00:00

There is racy issue between smb2 session log off and smb2 session setup. It will cause user-after-free from session log off. This add session_lock when setting SMB2_SESSION_EXPIRED and referece count to session struct not to free session while it is being used. Cc: stable@vger.kernel.org # v5.15+ Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-25282 Signed-off-by: Namjae Jeon Signed-off-by: Steve French