From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: Mon, 6 Apr 2026 13:46:48 +0000 (+0200)
Subject: ksmbd: fix mechToken leak when SPNEGO decode fails after token alloc
X-Git-Tag: v7.1-rc1~136^2~6
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=ad0057fb91218914d6c98268718ceb9d59b388e1;p=thirdparty%2Fkernel%2Flinux.git

ksmbd: fix mechToken leak when SPNEGO decode fails after token alloc

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>
---

diff --git a/fs/smb/server/connection.c b/fs/smb/server/connection.c
index 1bb2081c492c3..26cfce344861f 100644
--- a/fs/smb/server/connection.c
+++ b/fs/smb/server/connection.c
@@ -96,6 +96,7 @@ void ksmbd_conn_free(struct ksmbd_conn *conn)
 	xa_destroy(&conn->sessions);
 	kvfree(conn->request_buf);
 	kfree(conn->preauth_info);
+	kfree(conn->mechToken);
 	if (atomic_dec_and_test(&conn->refcnt)) {
 		conn->transport->ops->free_transport(conn->transport);
 		kfree(conn);
diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index c61fcc88d6f28..10ae77dae5a1b 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -1915,7 +1915,7 @@ 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;
 	}