[ofa-general] Re: patch: support long (above 14 bytes) HW addresses in arp_ioctl

[Constantine Gavrilov]

Try to resend as with a "web-friendly version". Hopefully, this can be 
read in the mail archive.

Constantine Gavrilov wrote:
> Updated version of the patch uses MAX_ADDR_LEN from netdevice.h as the 
> maximal length of MAC address.
>
> Constantine Gavrilov wrote:
>> While working with OFED infiniband stack that uses 20 byte long HW 
>> addresses for IP over IB, I have paid attention to the following  
>> arp_ioctl problem.
>>
>> The ioctl uses a data structure that limits a length of HW address to 
>> 14 bytes. The IP stack and the arp cache code do not have that 
>> limitation. This leads to the following problems:
>>
>> * arp_ioctl cannot be used to set, get, or delete arp entries for 
>> those adapters that have HW addresses longer than 14 bytes
>> * arp_ioctl will corrupt the kernel and user memory when this ioctl 
>> is used on the adapters that have HW addresses longer that 14 bytes.  
>> This is because when copying the HW address, the arp_ioctl code 
>> copies dev->addr_len bytes without checking that addr_len is not 
>> above 14 bytes. This is done both for copy_to_user() and memcpy() 
>> calls on kernel data structures allocated on stack. The memcpy() call 
>> in particular, will corrupt kernel stack.
>>
>> Attached please find the patch that fixes both problems. In addition, 
>> the patch changes the maximal number of bytes for HW address that 
>> will be seen in /proc/net/arp from ~10 to ~30. Without the last 
>> change, output of /proc/net/arp truncates the the large MAC entries, 
>> which makes the arp utility useless.
>>
>> The patch does not change the existing ABI but extends it.  The 
>> kernel structure used in arp_ioctl calls is changed to support larger 
>> addresses, while the user-space structure is extended by appending 
>> extra-space to the end of the structure if ATF_NEWARPCTL -- a new 
>> flag  -- is set in arp_flags of existing user-space structure. This 
>> allows avoiding big changes to the existing code while preserving the 
>> ABI compatibility.
>>
>

-- 
----------------------------------------
Constantine Gavrilov
Kernel Developer
Platform Group
XIV, an IBM global brand 
1 Azrieli Center, Tel-Aviv
Phone: +972-3-6074672
Fax:   +972-3-6959749
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