[PATCH 5.4 12/43] hdlc_ppp: add range checks in ppp_cp_parse_cr()

Greg Kroah-Hartman
2020-09-25T12:53:09Z

From: Dan Carpenter <dan.carpenter@oracle.com>

[ Upstream commit 66d42ed8b25b64eb63111a2b8582c5afc8bf1105 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/wan/hdlc_ppp.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

--- 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_d
}

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_d
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_d
}
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_d
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)