[PATCH 3.16 142/204] SMB: fix validate negotiate info uninitialised memory use

[Ben Hutchings]

3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

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

From: David Disseldorp <ddiss@xxxxxxx>

commit a2d9daad1d2dfbd307ab158044d1c323d7babbde upstream.

An undersize validate negotiate info server response causes the client
to use uninitialised memory for struct validate_negotiate_info_rsp
comparisons of Dialect, SecurityMode and/or Capabilities members.

Link: https://bugzilla.samba.org/show_bug.cgi?id=13092
Fixes: 7db0a6efdc3e ("SMB3: Work around mount failure when using SMB3 dialect to Macs")
Signed-off-by: David Disseldorp <ddiss@xxxxxxx>
Reviewed-by: Pavel Shilovsky <pshilov@xxxxxxxxxxxxx>
Signed-off-by: Steve French <smfrench@xxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/cifs/smb2pdu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -535,7 +535,8 @@ int smb3_validate_negotiate(const unsign
 			 rsplen);
 
 		/* relax check since Mac returns max bufsize allowed on ioctl */
-		if (rsplen > CIFSMaxBufSize)
+		if ((rsplen > CIFSMaxBufSize)
+		     || (rsplen < sizeof(struct validate_negotiate_info_rsp)))
 			goto err_rsp_free;
 	}