cvs commit: src/sys/dev/ath if_ath.c src/sys/dev/ipw if_ipw.c src/sys/dev/iwi if_iwi.c src/sys/dev/ral rt2560.c rt2661.c src/sys/dev/usb if_ural.c src/sys/dev/wi if_wi.c src/sys/net bpf.c bpf.h bpfdesc.h if_disc.c if_gif.c if_gre.c if_loop.c if_sl.c ...

Christian S.J. Peron csjp at
Fri Jun 2 20:01:07 UTC 2006

csjp        2006-06-02 19:59:33 UTC

  FreeBSD src repository

  Modified files:
    sys/dev/ath          if_ath.c 
    sys/dev/ipw          if_ipw.c 
    sys/dev/iwi          if_iwi.c 
    sys/dev/ral          rt2560.c rt2661.c 
    sys/dev/usb          if_ural.c 
    sys/dev/wi           if_wi.c 
    sys/net              bpf.c bpf.h bpfdesc.h if_disc.c if_gif.c 
                         if_gre.c if_loop.c if_sl.c if_stf.c 
    sys/net80211         ieee80211_input.c 
    sys/netinet          ip_carp.c ip_gre.c 
  Fix the following bpf(4) race condition which can result in a panic:
          (1) bpf peer attaches to interface netif0
          (2) Packet is received by netif0
          (3) ifp->if_bpf pointer is checked and handed off to bpf
          (4) bpf peer detaches from netif0 resulting in ifp->if_bpf being
              initialized to NULL.
          (5) ifp->if_bpf is dereferenced by bpf machinery
          (6) Kaboom
  This race condition likely explains the various different kernel panics
  reported around sending SIGINT to tcpdump or dhclient processes. But really
  this race can result in kernel panics anywhere you have frequent bpf attach
  and detach operations with high packet per second load.
  Summary of changes:
  - Remove the bpf interface's "driverp" member
  - When we attach bpf interfaces, we now set the ifp->if_bpf member to the
    bpf interface structure. Once this is done, ifp->if_bpf should never be
    NULL. [1]
  - Introduce bpf_peers_present function, an inline operation which will do
    a lockless read bpf peer list associated with the interface. It should
    be noted that the bpf code will pickup the bpf_interface lock before adding
    or removing bpf peers. This should serialize the access to the bpf descriptor
    list, removing the race.
  - Expose the bpf_if structure in bpf.h so that the bpf_peers_present function
    can use it. This also removes the struct bpf_if; hack that was there.
  - Adjust all consumers of the raw if_bpf structure to use bpf_peers_present
  Now what happens is:
          (1) Packet is received by netif0
          (2) Check to see if bpf descriptor list is empty
          (3) Pickup the bpf interface lock
          (4) Hand packet off to process
  From the attach/detach side:
          (1) Pickup the bpf interface lock
          (2) Add/remove from bpf descriptor list
  Now that we are storing the bpf interface structure with the ifnet, there is
  is no need to walk the bpf interface list to locate the correct bpf interface.
  We now simply look up the interface, and initialize the pointer. This has a
  nice side effect of changing a bpf interface attach operation from O(N) (where
  N is the number of bpf interfaces), to O(1).
  [1] From now on, we can no longer check ifp->if_bpf to tell us whether or
      not we have any bpf peers that might be interested in receiving packets.
  In collaboration with:  sam@
  MFC after:      1 month
  Revision  Changes    Path
  1.145     +4 -3      src/sys/dev/ath/if_ath.c
  1.20      +2 -2      src/sys/dev/ipw/if_ipw.c
  1.37      +2 -2      src/sys/dev/iwi/if_iwi.c
  1.5       +7 -7      src/sys/dev/ral/rt2560.c
  1.6       +3 -3      src/sys/dev/ral/rt2661.c
  1.39      +3 -3      src/sys/dev/usb/if_ural.c
  1.196     +3 -3      src/sys/dev/wi/if_wi.c
  1.166     +24 -71    src/sys/net/bpf.c
  1.41      +22 -4     src/sys/net/bpf.h
  1.34      +0 -13     src/sys/net/bpfdesc.h
  1.52      +1 -1      src/sys/net/if_disc.c
  1.60      +2 -4      src/sys/net/if_gif.c
  1.42      +1 -1      src/sys/net/if_gre.c
  1.109     +1 -1      src/sys/net/if_loop.c
  1.132     +4 -4      src/sys/net/if_sl.c
  1.54      +2 -2      src/sys/net/if_stf.c
  1.155     +1 -1      src/sys/net/if_tun.c
  1.91      +4 -4      src/sys/net80211/ieee80211_input.c
  1.40      +1 -1      src/sys/netinet/ip_carp.c
  1.24      +2 -2      src/sys/netinet/ip_gre.c

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