Il 06/09/2012 14:08, Ric Wheeler ha scritto: >> According to the standard, the translation layer can write a >> user-provided pattern to every sector in the disk. It's an optional >> feature and libata doesn't do that, but it is still possible. > > It is not possible today with our stack though, any patch that would > change that would also need to be vetted. It is not possible with SATA disks, but native SCSI disks might well interpret FORMAT UNIT destructively. >>> I don't see allowing anyone who can open the device to zero the data as >>> better though :) >> Note: anyone who can open it for writing! And they can just as well >> issue WRITE, it just takes a little more effort than with WRITE SAME. :) >> If you only have read access, you cannot issue WRITE or FORMAT UNIT, >> and with this patch you will not be able to issue WRITE SAME. > > This just seems like an argument over whether or not capabilities make > sense. In general, anything as destructive as a single CDB that can kill > all of your data should be tightly controlled. In practice, a single write to the first MB of the disk is just as destructive. For that you do not even need a SCSI command. > Pushing more code in the data path is not where we are going - we > routinely need to disable IO scheduling for example when driving IO to > high speed/low latency devices and are actively looking at how to tackle > other performance bottlenecks in the stack. I am not talking about the regular data path, only of SG_IO. > I don't see a strong reason that our existing scheme (root or > CAP_SYS_RAWIO access) prevents you from doing what you need to do. Here are three: - CAP_SYS_RAWIO partly bypasses DAC; you can issue destructive commands even if you only opened the disk for reading. CAP_SYS_RAWIO also gives access to _really_ destructive commands (WRITE BUFFER and PERSISTENT RESERVE OUT for example). - CAP_SYS_RAWIO lets you send SCSI commands to partitions, and they will gladly read/write the disk going outside the boundaries of the partition. Changing this behavior was rejected upstream already. - CAP_SYS_RAWIO also gives access to I/O ports, mmap at address 0, and too many other insecure things. All the above mean that: - any application using CAP_SYS_RAWIO would have to implement its own whitelisting, even if just to duplicate what is done in the kernel; - exploiting a CAP_SYS_RAWIO process leads to root too easily, and it is not possible to give the capability to anything that will run in a hostile environment (in my case QEMU). Paolo -- 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
