[PATCH 6.1 1002/1067] ksmbd: fix mechToken leak when SPNEGO decode fails after token alloc

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Greg Kroah-Hartman <[email protected]>

[ 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 <[email protected]>
Cc: Steve French <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Tom Talpey <[email protected]>
Cc: [email protected]
Cc: <[email protected]>
Assisted-by: gregkh_clanker_t1000
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Acked-by: Namjae Jeon <[email protected]>
Signed-off-by: Steve French <[email protected]>
Stable-dep-of: c1016dd1d8b2 ("ksmbd: track the connection owning a byte-range lock")
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 fs/smb/server/connection.c |    1 +
 fs/smb/server/smb2pdu.c    |    2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

--- a/fs/smb/server/connection.c
+++ b/fs/smb/server/connection.c
@@ -39,6 +39,7 @@ void ksmbd_conn_free(struct ksmbd_conn *
 	xa_destroy(&conn->sessions);
 	kvfree(conn->request_buf);
 	kfree(conn->preauth_info);
+	kfree(conn->mechToken);
 	kfree(conn);
 }
 
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -1909,7 +1909,7 @@ out_err:
 	else if (rc)
 		rsp->hdr.Status = STATUS_LOGON_FAILURE;
 
-	if (conn->use_spnego && conn->mechToken) {
+	if (conn->mechToken) {
 		kfree(conn->mechToken);
 		conn->mechToken = NULL;
 	}