• Guillaume Nault's avatar
    pppoe: take ->needed_headroom of lower device into account on xmit · 02612bb0
    Guillaume Nault authored
    In pppoe_sendmsg(), reserving dev->hard_header_len bytes of headroom
    was probably fine before the introduction of ->needed_headroom in
    commit f5184d26 ("net: Allow netdevices to specify needed head/tailroom").
    But now, virtual devices typically advertise the size of their overhead
    in dev->needed_headroom, so we must also take it into account in
    Allocation size of skb is also updated to take dev->needed_tailroom
    into account and replace the arbitrary 32 bytes with the real size of
    a PPPoE header.
    This issue was discovered by syzbot, who connected a pppoe socket to a
    gre device which had dev->header_ops->create == ipgre_header and
    dev->hard_header_len == 0. Therefore, PPPoE didn't reserve any
    headroom, and dev_hard_header() crashed when ipgre_header() tried to
    prepend its header to skb->data.
    skbuff: skb_under_panic: text:000000001d390b3a len:31 put:24
    head:00000000d8ed776f data:000000008150e823 tail:0x7 end:0xc0 dev:gre0
    ------------[ cut here ]------------
    kernel BUG at net/core/skbuff.c:104!
    invalid opcode: 0000 [#1] SMP KASAN
    Dumping ftrace buffer:
        (ftrace buffer empty)
    Modules linked in:
    CPU: 1 PID: 3670 Comm: syzkaller801466 Not tainted
    4.15.0-rc7-next-20180115+ #97
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
    Google 01/01/2011
    RIP: 0010:skb_panic+0x162/0x1f0 net/core/skbuff.c:100
    RSP: 0018:ffff8801d9bd7840 EFLAGS: 00010282
    RAX: 0000000000000083 RBX: ffff8801d4f083c0 RCX: 0000000000000000
    RDX: 0000000000000083 RSI: 1ffff1003b37ae92 RDI: ffffed003b37aefc
    RBP: ffff8801d9bd78a8 R08: 1ffff1003b37ae8a R09: 0000000000000000
    R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff86200de0
    R13: ffffffff84a981ad R14: 0000000000000018 R15: ffff8801d2d34180
    FS:  00000000019c4880(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00000000208bc000 CR3: 00000001d9111001 CR4: 00000000001606e0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
      skb_under_panic net/core/skbuff.c:114 [inline]
      skb_push+0xce/0xf0 net/core/skbuff.c:1714
      ipgre_header+0x6d/0x4e0 net/ipv4/ip_gre.c:879
      dev_hard_header include/linux/netdevice.h:2723 [inline]
      pppoe_sendmsg+0x58e/0x8b0 drivers/net/ppp/pppoe.c:890
      sock_sendmsg_nosec net/socket.c:630 [inline]
      sock_sendmsg+0xca/0x110 net/socket.c:640
      sock_write_iter+0x31a/0x5d0 net/socket.c:909
      call_write_iter include/linux/fs.h:1775 [inline]
      do_iter_readv_writev+0x525/0x7f0 fs/read_write.c:653
      do_iter_write+0x154/0x540 fs/read_write.c:932
      vfs_writev+0x18a/0x340 fs/read_write.c:977
      do_writev+0xfc/0x2a0 fs/read_write.c:1012
      SYSC_writev fs/read_write.c:1085 [inline]
      SyS_writev+0x27/0x30 fs/read_write.c:1082
    Admittedly PPPoE shouldn't be allowed to run on non Ethernet-like
    interfaces, but reserving space for ->needed_headroom is a more
    fundamental issue that needs to be addressed first.
    Same problem exists for __pppoe_xmit(), which also needs to take
    dev->needed_headroom into account in skb_cow_head().
    Fixes: f5184d26 ("net: Allow netdevices to specify needed head/tailroom")
    Reported-by: syzbot+ed0838d0fa4c4f2b528e20286e6dc63effc7c14d@syzkaller.appspotmail.com
    Signed-off-by: default avatarGuillaume Nault <g.nault@alphalink.fr>
    Reviewed-by: default avatarXin Long <lucien.xin@gmail.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
pppoe.c 27.5 KB