On 01/22/2019 06:30 PM, Jacob Wen wrote:
> Use pskb_may_pull() to make sure the optional fields are in skb linear
> parts.
>
> Signed-off-by: Jacob Wen <jian.w....@oracle.com>
> ---
> v1: fix warning: ISO C90 forbids mixed declarations and code
> ---
> net/l2tp/l2tp_core.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> index 26f1d435696a..c0dfa2bcd218 100644
> --- a/net/l2tp/l2tp_core.c
> +++ b/net/l2tp/l2tp_core.c
> @@ -627,6 +627,8 @@ void l2tp_recv_common(struct l2tp_session *session,
> struct sk_buff *skb,
>
> /* Parse and check optional cookie */
> if (session->peer_cookie_len > 0) {
> + if (!pskb_may_pull(skb, ptr - optr + session->peer_cookie_len))
> + goto discard;
This is completely buggy.
After pskb_may_pull(), the ptr and optr pointers might point to freed data.
So the memcmp() might crash hard.
> if (memcmp(ptr, &session->peer_cookie[0],
> session->peer_cookie_len)) {
> l2tp_info(tunnel, L2TP_MSG_DATA,
> "%s: cookie mismatch (%u/%u). Discarding.\n",
> @@ -649,6 +651,8 @@ void l2tp_recv_common(struct l2tp_session *session,
> struct sk_buff *skb,
> L2TP_SKB_CB(skb)->has_seq = 0;
> if (tunnel->version == L2TP_HDR_VER_2) {
> if (hdrflags & L2TP_HDRFLAG_S) {
> + if (!pskb_may_pull(skb, ptr - optr + 4))
> + goto discard;
> ns = ntohs(*(__be16 *) ptr);
> ptr += 2;
> nr = ntohs(*(__be16 *) ptr);
> @@ -663,8 +667,12 @@ void l2tp_recv_common(struct l2tp_session *session,
> struct sk_buff *skb,
> session->name, ns, nr, session->nr);
> }
> } else if (session->l2specific_type == L2TP_L2SPECTYPE_DEFAULT) {
> - u32 l2h = ntohl(*(__be32 *) ptr);
> + u32 l2h;
> +
> + if (!pskb_may_pull(skb, ptr - optr + 4))
> + goto discard;
>
> + l2h = ntohl(*(__be32 *) ptr);
> if (l2h & 0x40000000) {
> ns = l2h & 0x00ffffff;
>
> @@ -729,6 +737,8 @@ void l2tp_recv_common(struct l2tp_session *session,
> struct sk_buff *skb,
> if (tunnel->version == L2TP_HDR_VER_2) {
> /* If offset bit set, skip it. */
> if (hdrflags & L2TP_HDRFLAG_O) {
> + if (!pskb_may_pull(skb, ptr - optr + 2))
> + goto discard;
> offset = ntohs(*(__be16 *)ptr);
> ptr += 2 + offset;
> }
>
