CVE-2026-72422

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

ksmbd: fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE

conn->preauth_info is shared connection state (struct preauth_integrity_info, kmalloc-96) that is allocated and freed by the SMB2 NEGOTIATE handler and read by the response send path.

smb2_handle_negotiate() allocates conn->preauth_info, and on a deassemble_neg_contexts() failure kfrees it and sets it to NULL. Both the allocation and the free/NULL happen under ksmbd_conn_lock(conn) (the connection srv_mutex), which is held across the whole handler body.

The response send path smb3_preauth_hash_rsp(), called from the send: block of __handle_ksmbd_work(), reads conn->preauth_info and dereferences conn->preauth_info->Preauth_HashValue (via ksmbd_gen_preauth_integrity_hash()) without taking conn_lock. When a client drives two SMB2 NEGOTIATE requests on the same connection, one worker can free conn->preauth_info on the failing-negotiate path while a concurrent send-path worker is reading it, producing a slab use-after-free read (KASAN-confirmed).

The send-path read tested conn->preauth_info for NULL but raced with the free that occurs between the NULL check and the dereference, so the NULL guard alone does not close the window.

Serialize the NEGOTIATE-branch read in smb3_preauth_hash_rsp() under ksmbd_conn_lock(conn) and re-check conn->preauth_info inside the lock. Because the negotiate handler holds conn_lock across its kfree + NULL assignment, a reader that also takes conn_lock either runs fully before the allocation or fully after the NULL store, and can never observe the freed-but-not-yet-NULLed pointer. ksmbd_gen_preauth_integrity_hash() takes no locks itself (it only computes a SHA-512 over the buffer), so no lock-ordering inversion is introduced, and conn_lock is a sleepable mutex which is safe on this send path (it already performs network I/O).

Affected Software

References

• https://git.kernel.org/stable/c/0c054227479ed7e36ebccb3a558bc0ef698264f6
• https://git.kernel.org/stable/c/16a1ecf39c217e3d164bd32ef2a4f650abc067fa
• https://git.kernel.org/stable/c/1c89da3baa2b1f269178afa87dc30479b8535776
• https://git.kernel.org/stable/c/7470511d085af1c7a043a60e53d52b512d5a10b1
• https://git.kernel.org/stable/c/77bb0bbfcc4e777ca653174689e5e363f8ee63d1
• https://git.kernel.org/stable/c/c7bef84740d1d57848c74f6f5b996606e43ea4fe
• https://git.kernel.org/stable/c/d0a469122e7bf8338fec1949fb1e8e1290ed8caa