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: Jiri Slaby <jslaby@suse.cz>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 88cfbc189558f75b4b508b849827eea18c3be7c0..a84612585fc89dfe9e143eac529302741bf48a74 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -565,6 +565,7 @@ 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);
@@ -1814,6 +1815,18 @@ 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,
@@ -3610,6 +3623,10 @@ 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 1035fa2d909c7f18c100266c85ec07bce4a73a97..ca086c0c2c085cb3f3ff00834644d05d8769e7e3 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;