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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: e022c2f07a ("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>
This commit is contained in:
Dan Carpenter 2020-09-09 12:46:48 +03:00 committed by David S. Miller
parent 7d3ba9360c
commit 66d42ed8b2
1 changed files with 11 additions and 5 deletions
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16
drivers/net/wan/hdlc_ppp.c
View File

@ -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)