hdlc_ppp: add range checks in ppp_cp_parse_cr()

There are a couple bugs here:
1) If opt[1] is zero then this results in a forever loop.  If the value
   is less than 2 then it is invalid.
2) It assumes that "len" is more than sizeof(valid_accm) or 6 which can
   result in memory corruption.

In the case of LCP_OPTION_ACCM, then  we should check "opt[1]" instead
of "len" because, if "opt[1]" is less than sizeof(valid_accm) then
"nak_len" gets out of sync and it can lead to memory corruption in the
next iterations through the loop.  In case of LCP_OPTION_MAGIC, the
only valid value for opt[1] is 6, but the code is trying to log invalid
data so we should only discard the data when "len" is less than 6
because that leads to a read overflow.

Reported-by: ChenNan Of Chaitin Security Research Lab  <whutchennan@gmail.com>
Fixes: e022c2f07ae5 ("WAN: new synchronous PPP implementation for generic HDLC.")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/wan/hdlc_ppp.c b/drivers/net/wan/hdlc_ppp.c
index 48ced3912576c7227abb980029a5383c3742a457..16f33d1ffbfb973b5c8a33851c7dfe057dc29a02 100644 (file)
--- a/drivers/net/wan/hdlc_ppp.c
+++ b/drivers/net/wan/hdlc_ppp.c
@@ -383,11 +383,8 @@ static void ppp_cp_parse_cr(struct net_device *dev, u16 pid, u8 id,
        }
 
        for (opt = data; len; len -= opt[1], opt += opt[1]) {
-               if (len < 2 || len < opt[1]) {
-                       dev->stats.rx_errors++;
-                       kfree(out);
-                       return; /* bad packet, drop silently */
-               }
+               if (len < 2 || opt[1] < 2 || len < opt[1])
+                       goto err_out;
 
                if (pid == PID_LCP)
                        switch (opt[0]) {
@@ -395,6 +392,8 @@ static void ppp_cp_parse_cr(struct net_device *dev, u16 pid, u8 id,
                                continue; /* MRU always OK and > 1500 bytes? */
 
                        case LCP_OPTION_ACCM: /* async control character map */
+                               if (opt[1] < sizeof(valid_accm))
+                                       goto err_out;
                                if (!memcmp(opt, valid_accm,
                                            sizeof(valid_accm)))
                                        continue;
@@ -406,6 +405,8 @@ static void ppp_cp_parse_cr(struct net_device *dev, u16 pid, u8 id,
                                }
                                break;
                        case LCP_OPTION_MAGIC:
+                               if (len < 6)
+                                       goto err_out;
                                if (opt[1] != 6 || (!opt[2] && !opt[3] &&
                                                    !opt[4] && !opt[5]))
                                        break; /* reject invalid magic number */
@@ -424,6 +425,11 @@ static void ppp_cp_parse_cr(struct net_device *dev, u16 pid, u8 id,
                ppp_cp_event(dev, pid, RCR_GOOD, CP_CONF_ACK, id, req_len, data);
 
        kfree(out);
+       return;
+
+err_out:
+       dev->stats.rx_errors++;
+       kfree(out);
 }
 
 static int ppp_rx(struct sk_buff *skb)