[PATCH 5.15.y 4/7] ksmbd: fix mechToken leak when SPNEGO decode fails after token alloc

[Sasha Levin <sashal@kernel.org>]

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

[ Upstream commit ad0057fb91218914d6c98268718ceb9d59b388e1 ]

The kernel ASN.1 BER decoder calls action callbacks incrementally as it
walks the input.  When ksmbd_decode_negTokenInit() reaches the mechToken
[2] OCTET STRING element, ksmbd_neg_token_alloc() allocates
conn->mechToken immediately via kmemdup_nul().  If a later element in
the same blob is malformed, then the decoder will return nonzero after
the allocation is already live.  This could happen if mechListMIC [3]
overrunse the enclosing SEQUENCE.

decode_negotiation_token() then sets conn->use_spnego = false because
both the negTokenInit and negTokenTarg grammars failed.  The cleanup at
the bottom of smb2_sess_setup() is gated on use_spnego:

	if (conn->use_spnego && conn->mechToken) {
		kfree(conn->mechToken);
		conn->mechToken = NULL;
	}

so the kfree is skipped, causing the mechToken to never be freed.

This codepath is reachable pre-authentication, so untrusted clients can
cause slow memory leaks on a server without even being properly
authenticated.

Fix this up by not checking check for use_spnego, as it's not required,
so the memory will always be properly freed.  At the same time, always
free the memory in ksmbd_conn_free() incase some other failure path
forgot to free it.

Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: Steve French <smfrench@gmail.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Tom Talpey <tom@talpey.com>
Cc: linux-cifs@vger.kernel.org
Cc: <stable@kernel.org>
Assisted-by: gregkh_clanker_t1000
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Stable-dep-of: c1016dd1d8b2 ("ksmbd: track the connection owning a byte-range lock")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/ksmbd/connection.c | 1 +
 fs/ksmbd/smb2pdu.c    | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/ksmbd/connection.c b/fs/ksmbd/connection.c
index 63815c4df1333e..524caba512e79a 100644
--- a/fs/ksmbd/connection.c
+++ b/fs/ksmbd/connection.c
@@ -39,6 +39,7 @@ void ksmbd_conn_free(struct ksmbd_conn *conn)
 	xa_destroy(&conn->sessions);
 	kvfree(conn->request_buf);
 	kfree(conn->preauth_info);
+	kfree(conn->mechToken);
 	kfree(conn);
 }
 
diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
index a31a1561540960..af1e386cedb43b 100644
--- a/fs/ksmbd/smb2pdu.c
+++ b/fs/ksmbd/smb2pdu.c
@@ -1920,7 +1920,7 @@ int smb2_sess_setup(struct ksmbd_work *work)
 	else if (rc)
 		rsp->hdr.Status = STATUS_LOGON_FAILURE;
 
-	if (conn->use_spnego && conn->mechToken) {
+	if (conn->mechToken) {
 		kfree(conn->mechToken);
 		conn->mechToken = NULL;
 	}
-- 
2.53.0