[PATCH 4/8] tftp: accept OACK + DATA datagrams only in certain states

[Enrico Scholz <enrico.scholz@sigma-chemnitz.de>]

These packets are valid in certain points of the transfer only and
accepting them too early or too late can corrupt internal states.

Reject them when they are unexpected.

Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
---
 fs/tftp.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/tftp.c b/fs/tftp.c
index 610483d23c40..fb6c368b3a64 100644
--- a/fs/tftp.c
+++ b/fs/tftp.c
@@ -690,6 +690,12 @@ static void tftp_recv(struct file_priv *priv,
 		break;
 
 	case TFTP_OACK:
+		if (priv->state != STATE_RRQ && priv->state != STATE_WRQ) {
+			pr_warn("OACK packet in %s state\n",
+				tftp_states[priv->state]);
+			break;
+		}
+
 		priv->tftp_con->udp->uh_dport = uh_sport;
 
 		if (tftp_parse_oack(priv, pkt, len) < 0) {
@@ -713,6 +719,12 @@ static void tftp_recv(struct file_priv *priv,
 			tftp_window_cache_reset(&priv->cache);
 		}
 
+		if (priv->state != STATE_RDATA) {
+			pr_warn("DATA packet in %s state\n",
+				tftp_states[priv->state]);
+			break;
+		}
+
 		tftp_handle_data(priv, block, pkt + 2, len);
 
 		break;
-- 
2.37.2