[SRU][J][PATCH 0/1] CVE-2025-37926

[Cengiz Can]

https://ubuntu.com/security/CVE-2025-37926

[ Impact ]

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix use-after-free in ksmbd_session_rpc_open

A UAF issue can occur due to a race condition between ksmbd_session_rpc_open()
and __session_rpc_close(). Add rpc_lock to the session to protect it.

[ Fix ]

jammy/linux: backported from a1f46c99d9ea

The fix adds a per-session rpc_lock (an rwsem) that serialises access to the
session RPC list, closing the race window between ksmbd_session_rpc_open() and
__session_rpc_close() that could otherwise lead to a use-after-free.

The backport keeps this tree's atomic_set(refcnt, 1) and initialises the new
rwsem; the unrelated refcnt drift from the upstream commit is not carried over.
GFP_KERNEL is used in place of the not-yet-defined KSMBD_DEFAULT_GFP, and the
affected file lives at fs/ksmbd/ rather than fs/smb/server/ in this tree.

[ Test Plan ]

Build and boot tested.

[ Where Problems Could Occur ]

A bad fix would affect systems that run the in-kernel ksmbd SMB server and
serve files to SMB clients, where the added locking could in principle change
RPC handling behaviour or, if wrong, introduce a deadlock under concurrent
session setup and teardown. Systems that do not load or use the ksmbd module,
including those that rely on user-space Samba instead, are not affected.

[ Other Info ]

Kybele flow-v11-25-ga27c0fa6. Reference: cc51ef1e/v1