[PATCH] net: bootp: Prevent buffer overflow to avoid leaking the RAM content

[Philippe Reynes]

From: Paul HENRYS <paul.henrys_ext at softathome.com>

CVE-2024-42040 describes a possible buffer overflow when calling
bootp_process_vendor() in bootp_handler() since the total length
of the packet is passed to bootp_process_vendor() without being
reduced to len-(offsetof(struct bootp_hdr,bp_vend)+4).

The packet length is also checked against its minimum size to avoid
reading data from struct bootp_hdr outside of the packet length.

From: Paul HENRYS <paul.henrys_ext at softathome.com>
Signed-off-by: Paul HENRYS <paul.henrys_ext at softathome.com>
---
 net/bootp.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/net/bootp.c b/net/bootp.c
index 19e7453daed..3ab00433bb8 100644
--- a/net/bootp.c
+++ b/net/bootp.c
@@ -379,6 +379,14 @@ static void bootp_handler(uchar *pkt, unsigned dest, struct in_addr sip,
 	debug("got BOOTP packet (src=%d, dst=%d, len=%d want_len=%zu)\n",
 	      src, dest, len, sizeof(struct bootp_hdr));
 
+	/* Check the minimum size of a BOOTP packet is respected.
+	 * A BOOTP packet is between 300 bytes and 576 bytes big
+	 */
+	if (len < offsetof(struct bootp_hdr, bp_vend) + 64) {
+		printf("Error: got an invalid BOOTP packet (len=%u)\n", len);
+		return;
+	}
+
 	bp = (struct bootp_hdr *)pkt;
 
 	/* Filter out pkts we don't want */
@@ -396,7 +404,8 @@ static void bootp_handler(uchar *pkt, unsigned dest, struct in_addr sip,
 
 	/* Retrieve extended information (we must parse the vendor area) */
 	if (net_read_u32((u32 *)&bp->bp_vend[0]) == htonl(BOOTP_VENDOR_MAGIC))
-		bootp_process_vendor((uchar *)&bp->bp_vend[4], len);
+		bootp_process_vendor((uchar *)&bp->bp_vend[4], len -
+				     (offsetof(struct bootp_hdr, bp_vend) + 4));
 
 	net_set_timeout_handler(0, (thand_f *)0);
 	bootstage_mark_name(BOOTSTAGE_ID_BOOTP_STOP, "bootp_stop");
-- 
2.43.0