Re: [PATCH] forcedeth: fix random memory scribbling bug

[Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>]

Jeff Garzik wrote:

> Manfred Spraul wrote:
>
> > Two critical bugs were found in forcedeth 0.47:
> > - TSO doesn't work.
> > - pci_map_single() for the rx buffers is called with size==0. This 
> > bug is critical, it causes random memory corruptions on systems with 
> > an iommu.
> >
> > Below is a minimal fix for both bugs, for inclusion into 2.6.15.
> > TSO will be fixed properly in the next version.
> > Tested on x86-64.
> >
> > Signed-Off-By: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
>
>
> 1) Why does forcedeth require a non-standard calculation for each 
> pci_map_single() call?
- skb->len is the wrong thing (tm), since it's 0 until skb_put().
- I have not found a field that contains the actual size of the data 
area of an skb.
- the results must be identical for map and unmap.
- I could recalculate the size of the allocation from np->rx_buf_sz, but 
I don't like that. Right now it would work, but it's too subtile that 
changing rx_buf_sz while there are outstanding rx buffers results in a 
iommu memory leak.
Therefore I decided to calculate the mapping size with "skb->end - 
skb->data": The size of the mapping for an skb is calculated by looking 
at fields in the skb, no knowledge about driver fields.

> 2) I have requested multiple times that you avoid MIME...
It's the first time that you complain about Content-Transfer-Encoding: 
7bit attachments.

> 3) Why disable TSO completely?  It sounds like it should default to 
> off, then permit enabling via ethtool.
The bugfix is in 0.49 - it's just a bit larger, I would consider it for 
2.5.16.

--
   Manfred