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

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.

Signed-off-by: Paul HENRYS <paul.henrys_ext@softathome.com>
Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>

diff --git a/net/bootp.c b/net/bootp.c
index a28d11cb3683985635a27283ee7e4e7b2d78a19e..64fca9a42d9856cd6d06c18a4166ce9ff33af0f8 100644 (file)
--- 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");