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    Subject[PATCH 5.19 051/365] net: tap: NULL pointer derefence in dev_parse_header_protocol when skb->dev is null
    Date
    From: Cezar Bulinaru <cbulinaru@gmail.com>

    commit 4f61f133f354853bc394ec7d6028adb9b02dd701 upstream.

    Fixes a NULL pointer derefence bug triggered from tap driver.
    When tap_get_user calls virtio_net_hdr_to_skb the skb->dev is null
    (in tap.c skb->dev is set after the call to virtio_net_hdr_to_skb)
    virtio_net_hdr_to_skb calls dev_parse_header_protocol which
    needs skb->dev field to be valid.

    The line that trigers the bug is in dev_parse_header_protocol
    (dev is at offset 0x10 from skb and is stored in RAX register)
    if (!dev->header_ops || !dev->header_ops->parse_protocol)
    22e1: mov 0x10(%rbx),%rax
    22e5: mov 0x230(%rax),%rax

    Setting skb->dev before the call in tap.c fixes the issue.

    BUG: kernel NULL pointer dereference, address: 0000000000000230
    RIP: 0010:virtio_net_hdr_to_skb.constprop.0+0x335/0x410 [tap]
    Code: c0 0f 85 b7 fd ff ff eb d4 41 39 c6 77 cf 29 c6 48 89 df 44 01 f6 e8 7a 79 83 c1 48 85 c0 0f 85 d9 fd ff ff eb b7 48 8b 43 10 <48> 8b 80 30 02 00 00 48 85 c0 74 55 48 8b 40 28 48 85 c0 74 4c 48
    RSP: 0018:ffffc90005c27c38 EFLAGS: 00010246
    RAX: 0000000000000000 RBX: ffff888298f25300 RCX: 0000000000000010
    RDX: 0000000000000005 RSI: ffffc90005c27cb6 RDI: ffff888298f25300
    RBP: ffffc90005c27c80 R08: 00000000ffffffea R09: 00000000000007e8
    R10: ffff88858ec77458 R11: 0000000000000000 R12: 0000000000000001
    R13: 0000000000000014 R14: ffffc90005c27e08 R15: ffffc90005c27cb6
    FS: 0000000000000000(0000) GS:ffff88858ec40000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000000000000230 CR3: 0000000281408006 CR4: 00000000003706e0
    Call Trace:
    tap_get_user+0x3f1/0x540 [tap]
    tap_sendmsg+0x56/0x362 [tap]
    ? get_tx_bufs+0xc2/0x1e0 [vhost_net]
    handle_tx_copy+0x114/0x670 [vhost_net]
    handle_tx+0xb0/0xe0 [vhost_net]
    handle_tx_kick+0x15/0x20 [vhost_net]
    vhost_worker+0x7b/0xc0 [vhost]
    ? vhost_vring_call_reset+0x40/0x40 [vhost]
    kthread+0xfa/0x120
    ? kthread_complete_and_exit+0x20/0x20
    ret_from_fork+0x1f/0x30

    Fixes: 924a9bc362a5 ("net: check if protocol extracted by virtio_net_hdr_set_proto is correct")
    Signed-off-by: Cezar Bulinaru <cbulinaru@gmail.com>
    Reviewed-by: Willem de Bruijn <willemb@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/tap.c | 20 +++++++++++---------
    1 file changed, 11 insertions(+), 9 deletions(-)

    --- a/drivers/net/tap.c
    +++ b/drivers/net/tap.c
    @@ -716,10 +716,20 @@ static ssize_t tap_get_user(struct tap_q
    skb_reset_mac_header(skb);
    skb->protocol = eth_hdr(skb)->h_proto;

    + rcu_read_lock();
    + tap = rcu_dereference(q->tap);
    + if (!tap) {
    + kfree_skb(skb);
    + rcu_read_unlock();
    + return total_len;
    + }
    + skb->dev = tap->dev;
    +
    if (vnet_hdr_len) {
    err = virtio_net_hdr_to_skb(skb, &vnet_hdr,
    tap_is_little_endian(q));
    if (err) {
    + rcu_read_unlock();
    drop_reason = SKB_DROP_REASON_DEV_HDR;
    goto err_kfree;
    }
    @@ -732,8 +742,6 @@ static ssize_t tap_get_user(struct tap_q
    __vlan_get_protocol(skb, skb->protocol, &depth) != 0)
    skb_set_network_header(skb, depth);

    - rcu_read_lock();
    - tap = rcu_dereference(q->tap);
    /* copy skb_ubuf_info for callback when skb has no error */
    if (zerocopy) {
    skb_zcopy_init(skb, msg_control);
    @@ -742,14 +750,8 @@ static ssize_t tap_get_user(struct tap_q
    uarg->callback(NULL, uarg, false);
    }

    - if (tap) {
    - skb->dev = tap->dev;
    - dev_queue_xmit(skb);
    - } else {
    - kfree_skb(skb);
    - }
    + dev_queue_xmit(skb);
    rcu_read_unlock();
    -
    return total_len;

    err_kfree:

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