Make the sanity-checks on the size of incoming packets much stricter. We now

enforce the following:

* Packet must have at least one byte of payload and four bytes of padding.
* Total packet length must not exceed 35000 bytes compressed.
* Total packet length including length field must be a multiple of cipher
  block size (or eight bytes).

The feebleness of our old checks was noticed by Ben Rudiak-Gould.

git-svn-id: svn://svn.tartarus.org/sgt/putty@5981 cda61777-01e9-0310-a592-d414129be87e

diff --git a/ssh.c b/ssh.c
index 66b316e..55cecbd 100644 (file)
--- a/ssh.c
+++ b/ssh.c
@@ -1267,7 +1267,8 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
      * _Completely_ silly lengths should be stomped on before they
      * do us any more damage.
      */
-    if (st->len < 0 || st->pad < 0 || st->len + st->pad < 0) {
+    if (st->len < 0 || st->len > 35000 || st->pad < 4 ||
+       st->len - st->pad < 1 || (st->len + 4) % st->cipherblk != 0) {
        bombout(("Incoming packet was garbled on decryption"));
        ssh_free_packet(st->pktin);
        crStop(NULL);