Re: [Qemu-devel] [PATCH v4 0/2] rtl8139: Fix buffer overflow in standard mode

[Stefan Hajnoczi]

On Tue, Sep 01, 2015 at 11:26:44AM -0400, Vladislav Yasevich wrote:
> When rtl8139 card is running in standard mode, it is very easy
> to overlflow and the receive buffer and get into a siutation
> where all packets are dropped.  Simply reproduction case is
> to ping the guest from the host with 6500 byte packets.  
> 
> There are actually 2 problems here.
>  1) When the rtl8129 buffer is overflow, the card emulation
>     returns the size of the packet back to queue transmission.
>     This signals successful reception even though the packet
>     has been dropped.  The proper solution is to return 0, so
>     that the packet is re-queued and will be resubmitted later.
> 
>  2) The RxBuffAddr pointer used to track where packet is to be written
>     is aligned on a 4 byte boundary thus potentially adding some padding
>     between packets.  This padding is ignored when checking for overflow
>     condition.  It is possible to craft the packet such that we would
>     fail to detect an overflow and trigger buffer overwrite.  Adding
>     padding to the overflow check resolves this issues.
> 
> V4: As Jason Wang correctly pointed out, the overflow check should
>     catch this.  The reason it wasn't catching was that it was ignorring
>     the padding that may exist between each packet.  Adding the padding
>     to the overflow check resolved the issue.  This becomes a much
>     simpler fix.
> 
> V3: Fix the second patch to correctly track unread and available buffer
>     speace.   Prior version used calculation for availble space to track
>     unread space which was wrong.
> 
> V2: instead of tracking buffer_full condition, changed the code, as
>     suggested by Stefan Hajnoczi, to track the number of unread bytes
>     instead.  We initialize it to 0 at the start, adjust it on every
>     receive from the network and read from the guest and can set
>     the number of unread of bytes to full buffer size when the buffer
>     full.
> 
> Vladislav Yasevich (2):
>   rtl8139: Fix receive buffer overflow check
>   rtl8139: Do not consume the packet during overflow in standard mode.
> 
>  hw/net/rtl8139.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> -- 
> 1.9.3
> 

Thanks, applied to my net tree:
https://github.com/stefanha/qemu/commits/net

Stefan