On Fri, 2013-05-24 at 17:02 +0900, Tejun Heo wrote: > On Fri, May 24, 2013 at 4:13 PM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > >> The same filtering table being applied to different classes of > >> hardware is a software bug, but my point is that the practive > >> essentially entrusts non-insignificant part of security enforcement to > >> the hardware itself. The variety of hardware in question is very wide > >> and significant portion has historically been known to be flaky. > > > > Unproven theory, and contradicted by actual practice. Bugs are more > > common in the handling of borderline conditions, not in the handling of > > unimplemented commands. > > > > If you want to be secure aginst buggy firmware, the commands you have to > > block are READ and WRITE. Check out the list of existing USB quirks. > > Well, I'd actually much prefer disabling CDB whitelisting for all !MMC > devices if at all possible. I'll go along with this. I'm also wondering what the problem would be if we just allowed all commands on either CAP_SYS_RAWIO or opening the device for write, so we just defer to the filesystem permissions and restricted read only opens to the basic all device opcodes. > You're basically arguing that because what > we have is already broken, it should be okay to break it further. > Also, RW commands having more quirks doesn't necessarily indicate that > they tend to be more broken. They just get hammered on a lot in > various ways so problems on those commands tend to be more noticeable. I agree with this, so finding a way to get rid of the opcode table seems to be what we need. > > You need to allow more commands. > > The count-me-out knob allows all commands. > > You cannot always allow all commands. > > Ergo, you cannot always use the count-me-out knob. Do we have a real world example of this? Getting the kernel out of the command filtering business does seem to be a good idea to me. > The thing is that both approaches aren't perfect here so you can make > similar type of argument from the other side. If the system wants to > give out raw hardware access to VMs, requiring it to delegate the > device fully could be reasonable. Not ideal but widening direct > command access by default is pretty nasty too. James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
