[Pkg-samba-maint] [samba] 06/15: CVE-2016-2019: libcli/smb: don't allow guest sessions if we require signing

[Jelmer Vernooij]

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jelmer pushed a commit to branch master
in repository samba.

commit 46b5e4aca6adb12a27efaad3bfe66c2d8a82ec95
Author: Stefan Metzmacher <metze at samba.org>
Date:   Wed Apr 20 11:26:57 2016 +0200

    CVE-2016-2019: libcli/smb: don't allow guest sessions if we require signing
    
    Note real anonymous sessions (with "" as username) don't hit this
    as we don't even call smb2cli_session_set_session_key() in that case.
    
    BUG: https://bugzilla.samba.org/show_bug.cgi?id=11860
    
    Signed-off-by: Stefan Metzmacher <metze at samba.org>
---
 libcli/smb/smbXcli_base.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/libcli/smb/smbXcli_base.c b/libcli/smb/smbXcli_base.c
index 4332374..691b8ff 100644
--- a/libcli/smb/smbXcli_base.c
+++ b/libcli/smb/smbXcli_base.c
@@ -5312,6 +5312,10 @@ bool smbXcli_session_is_guest(struct smbXcli_session *session)
 		return false;
 	}
 
+	if (session->conn->mandatory_signing) {
+		return false;
+	}
+
 	if (session->conn->protocol >= PROTOCOL_SMB2_02) {
 		if (session->smb2->session_flags & SMB2_SESSION_FLAG_IS_GUEST) {
 			return true;
@@ -5571,7 +5575,7 @@ NTSTATUS smb2cli_session_set_session_key(struct smbXcli_session *session,
 					 const struct iovec *recv_iov)
 {
 	struct smbXcli_conn *conn = session->conn;
-	uint16_t no_sign_flags;
+	uint16_t no_sign_flags = 0;
 	uint8_t session_key[16];
 	bool check_signature = true;
 	uint32_t hdr_flags;
@@ -5596,7 +5600,18 @@ NTSTATUS smb2cli_session_set_session_key(struct smbXcli_session *session,
 		return NT_STATUS_INVALID_PARAMETER_MIX;
 	}
 
-	no_sign_flags = SMB2_SESSION_FLAG_IS_GUEST | SMB2_SESSION_FLAG_IS_NULL;
+	if (!conn->mandatory_signing) {
+		/*
+		 * only allow guest sessions without
+		 * mandatory signing.
+		 *
+		 * If we try an authentication with username != ""
+		 * and the server let us in without verifying the
+		 * password we don't have a negotiated session key
+		 * for signing.
+		 */
+		no_sign_flags = SMB2_SESSION_FLAG_IS_GUEST;
+	}
 
 	if (session->smb2->session_flags & no_sign_flags) {
 		session->smb2->should_sign = false;

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