packet: handle too big packets for PACKET_V3

[ Upstream commit dc808110bb62b64a448696ecac3938902c92e1ab ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 48a6a93db29602c032fe254d4a1d41cbc7b3f051..48b181797d7b5dc652bc374ad310569456eaaeea 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -635,6 +635,7 @@ 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);
@@ -1946,6 +1947,18 @@ 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,
@@ -3779,6 +3792,10 @@ 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 eb9580a6b25ff4474a7af54900efbe2579325d00..cdddf6a303996b1a512a7a3896362acc31635f0e 100644 (file)
--- 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;