target/linux/generic/pending-4.14/900-gen_stats-fix-netlink-stats-padding.patch

   1 The gen_stats facility will add a header for the toplevel nlattr of type
   2 TCA_STATS2 that contains all stats added by qdisc callbacks. A reference
   3 to this header is stored in the gnet_dump struct, and when all the
   4 per-qdisc callbacks have finished adding their stats, the length of the
   5 containing header will be adjusted to the right value.
   6
   7 However, on architectures that need padding (i.e., that don't set
   8 CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS), the padding nlattr is added
   9 before the stats, which means that the stored pointer will point to the
  10 padding, and so when the header is fixed up, the result is just a very
  11 big padding nlattr. Because most qdiscs also supply the legacy TCA_STATS
  12 struct, this problem has been mostly invisible, but we exposed it with
  13 the netlink attribute-based statistics in CAKE.
  14
  15 Fix the issue by fixing up the stored pointer if it points to a padding
  16 nlattr.
  17
  18 Tested-by: Pete Heist <pete@heistp.net>
  19 Tested-by: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>
  20 Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
  21 ---
  22  net/core/gen_stats.c |   16 ++++++++++++++--
  23  1 file changed, 14 insertions(+), 2 deletions(-)
  24
  25 --- a/net/core/gen_stats.c
  26 +++ b/net/core/gen_stats.c
  27 @@ -77,8 +77,20 @@ gnet_stats_start_copy_compat(struct sk_b
  28                 d->lock = lock;
  29                 spin_lock_bh(lock);
  30         }
  31 -       if (d->tail)
  32 -               return gnet_stats_copy(d, type, NULL, 0, padattr);
  33 +       if (d->tail) {
  34 +               int ret = gnet_stats_copy(d, type, NULL, 0, padattr);
  35 +
  36 +               /* The initial attribute added in gnet_stats_copy() may be
  37 +                * preceded by a padding attribute, in which case d->tail will
  38 +                * end up pointing at the padding instead of the real attribute.
  39 +                * Fix this so gnet_stats_finish_copy() adjusts the length of
  40 +                * the right attribute.
  41 +                */
  42 +               if (ret == 0 && d->tail->nla_type == padattr)
  43 +                       d->tail = (struct nlattr *)((char *)d->tail +
  44 +                                                   NLA_ALIGN(d->tail->nla_len));
  45 +               return ret;
  46 +       }
  47
  48         return 0;
  49  }