ksmbd: fix wrong next length validation of ea buffer in smb2_set_ea()

There are multiple smb2_ea_info buffers in FILE_FULL_EA_INFORMATION request
from client. ksmbd find next smb2_ea_info using ->NextEntryOffset of
current smb2_ea_info. ksmbd need to validate buffer length Before
accessing the next ea. ksmbd should check buffer length using buf_len,
not next variable. next is the start offset of current ea that got from
previous ea.

Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-21598
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: namjaejeon

fs/smb/server/smb2pdu.c

@@ -2324,9 +2324,16 @@ static int smb2_set_ea(struct smb2_ea_info *eabuf, unsigned int buf_len,
 			break;
 		buf_len -= next;
 		eabuf = (struct smb2_ea_info *)((char *)eabuf + next);
-		if (next < (u32)eabuf->EaNameLength + le16_to_cpu(eabuf->EaValueLength))
+		if (buf_len < sizeof(struct smb2_ea_info)) {
+			rc = -EINVAL;
 			break;
+		}
 
+		if (buf_len < sizeof(struct smb2_ea_info) + eabuf->EaNameLength +
+				le16_to_cpu(eabuf->EaValueLength)) {
+			rc = -EINVAL;
+			break;
+		}
 	} while (next != 0);
 
 	kfree(attr_name);