• Daniel Borkmann's avatar
    net: sctp: fix skb_over_panic when receiving malformed ASCONF chunks · 9de7922b
    Daniel Borkmann authored
    Commit 6f4c618d ("SCTP : Add paramters validity check for
    ASCONF chunk") added basic verification of ASCONF chunks, however,
    it is still possible to remotely crash a server by sending a
    special crafted ASCONF chunk, even up to pre 2.6.12 kernels:
    
    skb_over_panic: text:ffffffffa01ea1c3 len:31056 put:30768
     head:ffff88011bd81800 data:ffff88011bd81800 tail:0x7950
     end:0x440 dev:<NULL>
     ------------[ cut here ]------------
    kernel BUG at net/core/skbuff.c:129!
    [...]
    Call Trace:
     <IRQ>
     [<ffffffff8144fb1c>] skb_put+0x5c/0x70
     [<ffffffffa01ea1c3>] sctp_addto_chunk+0x63/0xd0 [sctp]
     [<ffffffffa01eadaf>] sctp_process_asconf+0x1af/0x540 [sctp]
     [<ffffffff8152d025>] ? _read_unlock_bh+0x15/0x20
     [<ffffffffa01e0038>] sctp_sf_do_asconf+0x168/0x240 [sctp]
     [<ffffffffa01e3751>] sctp_do_sm+0x71/0x1210 [sctp]
     [<ffffffff8147645d>] ? fib_rules_lookup+0xad/0xf0
     [<ffffffffa01e6b22>] ? sctp_cmp_addr_exact+0x32/0x40 [sctp]
     [<ffffffffa01e8393>] sctp_assoc_bh_rcv+0xd3/0x180 [sctp]
     [<ffffffffa01ee986>] sctp_inq_push+0x56/0x80 [sctp]
     [<ffffffffa01fcc42>] sctp_rcv+0x982/0xa10 [sctp]
     [<ffffffffa01d5123>] ? ipt_local_in_hook+0x23/0x28 [iptable_filter]
     [<ffffffff8148bdc9>] ? nf_iterate+0x69/0xb0
     [<ffffffff81496d10>] ? ip_local_deliver_finish+0x0/0x2d0
     [<ffffffff8148bf86>] ? nf_hook_slow+0x76/0x120
     [<ffffffff81496d10>] ? ip_local_deliver_finish+0x0/0x2d0
     [<ffffffff81496ded>] ip_local_deliver_finish+0xdd/0x2d0
     [<ffffffff81497078>] ip_local_deliver+0x98/0xa0
     [<ffffffff8149653d>] ip_rcv_finish+0x12d/0x440
     [<ffffffff81496ac5>] ip_rcv+0x275/0x350
     [<ffffffff8145c88b>] __netif_receive_skb+0x4ab/0x750
     [<ffffffff81460588>] netif_receive_skb+0x58/0x60
    
    This can be triggered e.g., through a simple scripted nmap
    connection scan injecting the chunk after the handshake, for
    example, ...
    
      -------------- INIT[ASCONF; ASCONF_ACK] ------------->
      <----------- INIT-ACK[ASCONF; ASCONF_ACK] ------------
      -------------------- COOKIE-ECHO -------------------->
      <-------------------- COOKIE-ACK ---------------------
      ------------------ ASCONF; UNKNOWN ------------------>
    
    ... where ASCONF chunk of length 280 contains 2 parameters ...
    
      1) Add IP address parameter (param length: 16)
      2) Add/del IP address parameter (param length: 255)
    
    ... followed by an UNKNOWN chunk of e.g. 4 bytes. Here, the
    Address Parameter in the ASCONF chunk is even missing, too.
    This is just an example and similarly-crafted ASCONF chunks
    could be used just as well.
    
    The ASCONF chunk passes through sctp_verify_asconf() as all
    parameters passed sanity checks, and after walking, we ended
    up successfully at the chunk end boundary, and thus may invoke
    sctp_process_asconf(). Parameter walking is done with
    WORD_ROUND() to take padding into account.
    
    In sctp_process_asconf()'s TLV processing, we may fail in
    sctp_process_asconf_param() e.g., due to removal of the IP
    address that is also the source address of the packet containing
    the ASCONF chunk, and thus we need to add all TLVs after the
    failure to our ASCONF response to remote via helper function
    sctp_add_asconf_response(), which basically invokes a
    sctp_addto_chunk() adding the error parameters to the given
    skb.
    
    When walking to the next parameter this time, we proceed
    with ...
    
      length = ntohs(asconf_param->param_hdr.length);
      asconf_param = (void *)asconf_param + length;
    
    ... instead of the WORD_ROUND()'ed length, thus resulting here
    in an off-by-one that leads to reading the follow-up garbage
    parameter length of 12336, and thus throwing an skb_over_panic
    for the reply when trying to sctp_addto_chunk() next time,
    which implicitly calls the skb_put() with that length.
    
    Fix it by using sctp_walk_params() [ which is also used in
    INIT parameter processing ] macro in the verification *and*
    in ASCONF processing: it will make sure we don't spill over,
    that we walk parameters WORD_ROUND()'ed. Moreover, we're being
    more defensive and guard against unknown parameter types and
    missized addresses.
    
    Joint work with Vlad Yasevich.
    
    Fixes: b896b82b ("[SCTP] ADDIP: Support for processing incoming ASCONF_ACK chunks.")
    Signed-off-by: default avatarDaniel Borkmann <dborkman@redhat.com>
    Signed-off-by: default avatarVlad Yasevich <vyasevich@gmail.com>
    Acked-by: default avatarNeil Horman <nhorman@tuxdriver.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    9de7922b
sm_statefuns.c 197 KB