2008/7/15 Jiri Slaby <jirislaby@gmail.com>:
quoted text
> When signal is noisy, hardware can use all RX buffers and since the last
> entry in the list is self-linked, it overwrites the entry until we link
> new buffers.
>
> Ensure that we don't free this last one until we are 100% sure that it
> is not used by the hardware anymore to not cause memory curruption as
> can be seen below.
>
> This is done by checking next buffer in the list. Even after that we
> know that the hardware refetched the new link and proceeded further
> (the next buffer is ready) we can finally free the overwritten buffer.
>
> We discard it since the status in its descriptor is overwritten (OR-ed
> by new status) too.
>
> =============================================================================
> BUG kmalloc-4096: Poison overwritten
> -----------------------------------------------------------------------------
>
> INFO: 0xffff810067419060-0xffff810067419667. First byte 0x8 instead of 0x6b
> INFO: Allocated in dev_alloc_skb+0x18/0x30 age=1118 cpu=1 pid=0
> INFO: Freed in skb_release_data+0x85/0xd0 age=1105 cpu=1 pid=3718
> INFO: Slab 0xffffe200019d0600 objects=7 used=0 fp=0xffff810067419048 flags=0x40000000000020c3
> INFO: Object 0xffff810067419048 @offset=4168 fp=0xffff81006741c120
>
> Bytes b4 0xffff810067419038:  4f 0b 02 00 01 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a O.......ZZZZZZZZ
>  Object 0xffff810067419048:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
>  Object 0xffff810067419058:  6b 6b 6b 6b 6b 6b 6b 6b 08 42 30 00 00 0b 6b 80 kkkkkkkk.B0...k.
>  Object 0xffff810067419068:  f0 5d 00 4f 62 08 a3 64 00 0c 42 16 52 e4 f0 5a 360].Ob.243d..B.R344360Z
>  Object 0xffff810067419078:  68 81 00 00 7b a5 b4 be 7d 3b 8f 53 cd d5 de 12 h...{245264276};.S315325336.
>  Object 0xffff810067419088:  96 10 0b 89 48 54 23 41 0f 4e 2d b9 37 c3 cb 29 ....HT#A.N-2717303313)
>  Object 0xffff810067419098:  d1 e0 de 14 8a 57 2a cc 3b 44 0d 78 7a 19 12 15 321340336..W*314;D.xz...
>  Object 0xffff8100674190a8:  a9 ec d4 35 a8 10 ec 8c 40 a7 06 0a 51 a7 48 bb 2513543245250.354.@247..Q247H273
>  Object 0xffff8100674190b8:  3e cf a1 c7 38 60 63 3f 51 15 c7 20 eb ba 65 30 >ϡ3078`c?Q.307.353272e0
>  Redzone 0xffff81006741a048:  bb bb bb bb bb bb bb bb                         273273273273273273273273
>  Padding 0xffff81006741a088:  5a 5a 5a 5a 5a 5a 5a 5a                         ZZZZZZZZ
> Pid: 3297, comm: ath5k_pci Not tainted 2.6.26-rc8-mm1_64 #427
>
> Call Trace:
>  [<ffffffff802a7306>] print_trailer+0xf6/0x150
>  [<ffffffff802a7485>] check_bytes_and_report+0x125/0x180
>  [<ffffffff802a75dc>] check_object+0xac/0x260
>  [<ffffffff802a9308>] __slab_alloc+0x368/0x6d0
>  [<ffffffff80544f82>] ? wireless_send_event+0x142/0x310
>  [<ffffffff804b1bd4>] ? __alloc_skb+0x44/0x150
>  [<ffffffff80544f82>] ? wireless_send_event+0x142/0x310
>  [<ffffffff802aa853>] __kmalloc_track_caller+0xc3/0xf0
>  [<ffffffff804b1bfe>] __alloc_skb+0x6e/0x150
> [... stack snipped]
>
> FIX kmalloc-4096: Restoring 0xffff810067419060-0xffff810067419667=0x6b
>
> FIX kmalloc-4096: Marking all objects used
>
> Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
> Cc: Nick Kossifidis <mickflemm@gmail.com>
> Cc: Luis R. Rodriguez <mcgrof@gmail.com>
> ---
>  drivers/net/wireless/ath5k/base.c |   32 +++++++++++++++++++++++++-------
>  drivers/net/wireless/ath5k/base.h |    2 +-
>  2 files changed, 26 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/wireless/ath5k/base.c b/drivers/net/wireless/ath5k/base.c
> index 12a9443..e9ec284 100644
> --- a/drivers/net/wireless/ath5k/base.c
> +++ b/drivers/net/wireless/ath5k/base.c
> @@ -1683,20 +1683,21 @@ ath5k_tasklet_rx(unsigned long data)
>        struct ath5k_rx_status rs = {};
>        struct sk_buff *skb;
>        struct ath5k_softc *sc = (void *)data;
> -       struct ath5k_buf *bf;
> +       struct ath5k_buf *bf, *bf_last;
>        struct ath5k_desc *ds;
>        int ret;
>        int hdrlen;
>        int pad;
>
>        spin_lock(&sc->rxbuflock);
> +       if (list_empty(&sc->rxbuf)) {
> +               ATH5K_WARN(sc, "empty rx buf pool\n");
> +               goto unlock;
> +       }
> +       bf_last = list_entry(sc->rxbuf.prev, struct ath5k_buf, list);
>        do {
>                rxs.flag = 0;
>
> -               if (unlikely(list_empty(&sc->rxbuf))) {
> -                       ATH5K_WARN(sc, "empty rx buf pool\n");
> -                       break;
> -               }
>                bf = list_first_entry(&sc->rxbuf, struct ath5k_buf, list);
>                BUG_ON(bf->skb == NULL);
>                skb = bf->skb;
> @@ -1706,8 +1707,24 @@ ath5k_tasklet_rx(unsigned long data)
>                pci_dma_sync_single_for_cpu(sc->pdev, sc->desc_daddr,
>                                sc->desc_len, PCI_DMA_FROMDEVICE);
>
> -               if (unlikely(ds->ds_link == bf->daddr)) /* this is the end */
> -                       break;
> +               /*
> +                * last buffer must not be freed to ensure proper hardware
> +                * function. When the hardware finishes also a packet next to
> +                * it, we are sure, it doesn't use it anymore and we can go on.
> +                */
> +               if (bf_last == bf)
> +                       bf->flags |= 1;
> +               if (bf->flags) {
> +                       struct ath5k_buf *bf_next = list_entry(bf->list.next,
> +                                       struct ath5k_buf, list);
> +                       ret = sc->ah->ah_proc_rx_desc(sc->ah, bf_next->desc,
> +                                       &rs);
> +                       if (ret)
> +                               break;
> +                       bf->flags &= ~1;
> +                       /* skip the overwritten one (even status is martian) */
> +                       goto next;
> +               }
>
>                ret = sc->ah->ah_proc_rx_desc(sc->ah, ds, &rs);
>                if (unlikely(ret == -EINPROGRESS))
> @@ -1817,6 +1834,7 @@ accept:
>  next:
>                list_move_tail(&bf->list, &sc->rxbuf);
>        } while (ath5k_rxbuf_setup(sc, bf) == 0);
> +unlock:
>        spin_unlock(&sc->rxbuflock);
>  }
>
> diff --git a/drivers/net/wireless/ath5k/base.h b/drivers/net/wireless/ath5k/base.h
> index 47f414b..d7e03e6 100644
> --- a/drivers/net/wireless/ath5k/base.h
> +++ b/drivers/net/wireless/ath5k/base.h
> @@ -56,7 +56,7 @@
>
>  struct ath5k_buf {
>        struct list_head        list;
> -       unsigned int            flags;  /* tx descriptor flags */
> +       unsigned int            flags;  /* rx descriptor flags */
>        struct ath5k_desc       *desc;  /* virtual addr of desc */
>        dma_addr_t              daddr;  /* physical addr of desc */
>        struct sk_buff          *skb;   /* skbuff for buf */
> --
> 1.5.6.2
>
>

Nice catch ;-)

Acked-by: Nick Kossifidis <mickflemm@gmail.com>

-- 
GPG ID: 0xD21DB2DB
As you read this post global entropy rises. Have Fun ;-)
Nick