Re: [PATCH] PCI/IOV: "virtfn4294967295\0" requires 17 bytes

["Alexey V. Vissarionov" <gremlin@altlinux.org>]

On 2022-12-18 22:19:24 +0000, Matthew Wilcox wrote:

 >>> Thank you for sending the patch over! However, if possible,
 >>> can you send it as plain text without any multi-part MIME
 >>> involved?
 >> ACK.
 >>> If possible, it would be nice to mention that this needed
 >>> to make sure that there is enough space to correctly
 >>> NULL-terminate the ID string.
 >> ACK.
 >> So, here goes the corrected text:
 >> Although unlikely, the 'id' value may be as big as 4294967295
 >> (uint32_max) and "virtfn4294967295\0" would require 17 bytes
 >> instead of 16 to make sure that buffer has enough space to
 >> properly NULL-terminate the ID string.
 > Wait, what? How can we get to a number that large for the
 > virtual function ID? devfn is 8 bits, bus is a further 8 bits.
 > Sure, domain is an extra 16 bits on top of that but I'm pretty
 > sure that virtual functions can't span multiple domains.
 > Unless that's changed recently? Even if they can, we'd need
 > to span 2^14 domains to get up to a billion IDs. That's a
 > hell of a system and I think overflowing here is the least
 > of our problems.

Possibly in some synthetic cases this may be achieved with some
specially crafted "BadPCI" (similar to "BadUSB") device...

 > So while this is typed as u32, I don't think it can get
 > anywhere close.

Anyway, the final decision is up to you.


-- 
Alexey V. Vissarionov
gremlin ПРИ altlinux ТЧК org; +vii-cmiii-ccxxix-lxxix-xlii
GPG: 0D92F19E1C0DC36E27F61A29CD17E2B43D879005 @ hkp://keys.gnupg.net