[PATCH v2 0/4] ksmbd: verify session setup requests before signing with their key

[Michail Andreas Michalopoulos]

ksmbd signs some SESSION_SETUP and error responses with a session's key
without having verified the request, which lets a peer that does not hold
the key obtain signatures made with it. This series fixes those cases and
makes ksmbd sign with the SMB 3.1.1 signing algorithm it negotiated.

1/4 verifies multichannel binding requests with the session signing key
    (MS-SMB2 3.3.5.2.4), as reported by Ian Bridges.
2/4 keeps the negotiated SMB 3.1.1 signing algorithm instead of always
    using AES-CMAC, and signs each key with its own algorithm.
3/4 verifies signed reauthentication requests and uses the channel key
    for session setup on a bound channel. A reauthentication with a
    forged signature used to get a response signed with the session key.
4/4 checks the MessageId and signature of a request before signing
    STATUS_NETWORK_SESSION_EXPIRED, also reported by Ian Bridges.

Changes since v1:
- 1/4 is new: verify the signature of session binding requests, as
  reported by Ian Bridges.
- 2/4 (v1 1/2): reset the negotiated signing state on every NEGOTIATE;
  Cc stable, since 3/4 depends on it.
- 3/4 and 4/4 are new.
- The AES-GMAC signing patch (v1 2/2) is dropped from this series and
  will be posted separately.

Testing, on a KASAN/lockdep UML kernel with ksmbd-tools: forged and
replayed binding, reauthentication and expired-session requests, also
inside compounds, get unsigned refusals with AES-CMAC and HMAC-SHA256;
randomized requests against these paths and concurrent bind/reauth/
logoff stress found no signed response to an unverified request and no
KASAN or lockdep report; the Linux cifs client works with SMB 2.1 to
3.1.1, signed and encrypted; smbtorture's session, signing, I/O,
compound, lock, oplock, lease, notify and ioctl suites give the same
results as without the series. Ian Bridges also tested an earlier
revision with his own probes and smbtorture. Not tested: Windows
clients, and Kerberos expiry with a real KDC (it was emulated with a
test-only change).

An AI assistant was used to draft the patches and as an independent
reviewer.

Michail Andreas Michalopoulos (4):
  ksmbd: verify the signature of session binding requests
  ksmbd: sign with the negotiated SMB 3.1.1 signing algorithm
  ksmbd: use the channel signing key for session setup on a bound
    channel
  ksmbd: check a request before signing STATUS_NETWORK_SESSION_EXPIRED

 fs/smb/server/auth.c              |  14 +++-
 fs/smb/server/auth.h              |   4 +-
 fs/smb/server/mgmt/user_session.c |   1 +
 fs/smb/server/mgmt/user_session.h |   2 +
 fs/smb/server/server.c            |  39 +++++++++-
 fs/smb/server/smb2ops.c           |   4 +-
 fs/smb/server/smb2pdu.c           | 114 +++++++++++++++++++++++++-----
 7 files changed, 154 insertions(+), 24 deletions(-)


base-commit: 05441d697f7f9a927264f4058cbbc6a03dfcac9d
-- 
2.43.0