[PATCH 13/13] tftp: add sanity check for OACK response

[Enrico Scholz <enrico.scholz@xxxxxxxxxxxxxxxxx>]

Catch bad 'blocksize' or 'windowsize' responses from the server.

Signed-off-by: Enrico Scholz <enrico.scholz@xxxxxxxxxxxxxxxxx>
---
 fs/tftp.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/fs/tftp.c b/fs/tftp.c
index 400209c26023..c6491b537481 100644
--- a/fs/tftp.c
+++ b/fs/tftp.c
@@ -290,7 +290,7 @@ static int tftp_poll(struct file_priv *priv)
 	return 0;
 }
 
-static void tftp_parse_oack(struct file_priv *priv, unsigned char *pkt, int len)
+static int tftp_parse_oack(struct file_priv *priv, unsigned char *pkt, int len)
 {
 	unsigned char *opt, *val, *s;
 
@@ -307,7 +307,7 @@ static void tftp_parse_oack(struct file_priv *priv, unsigned char *pkt, int len)
 		opt = s;
 		val = s + strlen(s) + 1;
 		if (val > s + len)
-			return;
+			break;
 		if (!strcmp(opt, "tsize"))
 			priv->filesize = simple_strtoull(val, NULL, 10);
 		if (!strcmp(opt, "blksize"))
@@ -317,6 +317,15 @@ static void tftp_parse_oack(struct file_priv *priv, unsigned char *pkt, int len)
 		pr_debug("OACK opt: %s val: %s\n", opt, val);
 		s = val + strlen(val) + 1;
 	}
+
+	if (priv->blocksize > TFTP_MTU_SIZE ||
+	    priv->windowsize > TFTP_MAX_WINDOW_SIZE ||
+	    priv->windowsize == 0) {
+		pr_warn("tftp: invalid oack response");
+		return -EINVAL;
+	}
+
+	return 0;
 }
 
 static void tftp_timer_reset(struct file_priv *priv)
@@ -498,10 +507,12 @@ static void tftp_recv(struct file_priv *priv,
 		break;
 
 	case TFTP_OACK:
-		tftp_parse_oack(priv, pkt, len);
 		priv->tftp_con->udp->uh_dport = uh_sport;
 
-		if (priv->push) {
+		if (tftp_parse_oack(priv, pkt, len) < 0) {
+			priv->err = -EINVAL;
+			priv->state = STATE_DONE;
+		} else if (priv->push) {
 			/* send first block */
 			priv->state = STATE_WDATA;
 			priv->block = 1;
-- 
2.36.1