packet: handle too big packets for PACKET_V3

af_packet can currently overwrite kernel memory by out of bound
accesses, because it assumed a [new] block can always hold one frame.

This is not generally the case, even if most existing tools do it right.

This patch clamps too long frames as API permits, and issue a one time
error on syslog.

[  394.357639] tpacket_rcv: packet too big, clamped from 5042 to 3966. macoff=82

In this example, packet header tp_snaplen was set to 3966,
and tp_len was set to 5042 (skb->len)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Fixes: f6fb8f100b80 ("af-packet: TPACKET_V3 flexible buffer implementation.")
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 18 insertions, 0 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 8d9f8042705a..93896d2092f6 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -632,6 +632,7 @@ static void init_prb_bdqc(struct packet_sock *po,
         p1->tov_in_jiffies = msecs_to_jiffies(p1->retire_blk_tov);
         p1->blk_sizeof_priv = req_u->req3.tp_sizeof_priv;
 
+        p1->max_frame_len = p1->kblk_size - BLK_PLUS_PRIV(p1->blk_sizeof_priv);
         prb_init_ft_ops(p1, req_u);
         prb_setup_retire_blk_timer(po, tx_ring);
         prb_open_block(p1, pbd);
@@ -1942,6 +1943,18 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
                         if ((int)snaplen < 0)
                                 snaplen = 0;
                 }
+        } else if (unlikely(macoff + snaplen >
+                            GET_PBDQC_FROM_RB(&po->rx_ring)->max_frame_len)) {
+                u32 nval;
+
+                nval = GET_PBDQC_FROM_RB(&po->rx_ring)->max_frame_len - macoff;
+                pr_err_once("tpacket_rcv: packet too big, clamped from %u to %u. macoff=%u\n",
+                            snaplen, nval, macoff);
+                snaplen = nval;
+                if (unlikely((int)snaplen < 0)) {
+                        snaplen = 0;
+                        macoff = GET_PBDQC_FROM_RB(&po->rx_ring)->max_frame_len;
+                }
         }
         spin_lock(&sk->sk_receive_queue.lock);
         h.raw = packet_current_rx_frame(po, skb,
@@ -3783,6 +3796,10 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
                         goto out;
                 if (unlikely(req->tp_block_size & (PAGE_SIZE - 1)))
                         goto out;
+                if (po->tp_version >= TPACKET_V3 &&
+                    (int)(req->tp_block_size -
+                          BLK_PLUS_PRIV(req_u->req3.tp_sizeof_priv)) <= 0)
+                        goto out;
                 if (unlikely(req->tp_frame_size < po->tp_hdrlen +
                                         po->tp_reserve))
                         goto out;
diff --git a/net/packet/internal.h b/net/packet/internal.h
index eb9580a6b25f..cdddf6a30399 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -29,6 +29,7 @@ struct tpacket_kbdq_core {
         char            *pkblk_start;
         char            *pkblk_end;
         int             kblk_size;
+        unsigned int    max_frame_len;
         unsigned int    knum_blocks;
         uint64_t        knxt_seq_num;
         char            *prev;