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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: e022c2f ("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> (cherry picked from commit 66d42ed) CVE-2020-25643 Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> Signed-off-by: Timo Aaltonen <timo.aaltonen@canonical.com>
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