[Bug 721] New: mdev.conf subsystem match is wrong

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=721

           Summary: mdev.conf subsystem match is wrong
           Product: Busybox
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: Other
        AssignedTo: unassigned at busybox.net
        ReportedBy: mjt+busybox at corpit.ru
                CC: busybox-cvs at busybox.net
   Estimated Hours: 0.0


In the code in util-linux/mdev.c, there's this fragment:

        /* Make path point to "subsystem/device_name" */
        if (path[5] == 'b') /* legacy /sys/block? */
                path += sizeof("/sys/") - 1;
        else
                path += sizeof("/sys/class/") - 1;

It assumes that the original path is starting either with "/sys/block" or
"/sys/class".  But this is only true when traversing sysfs for `mdev -s', ie,
"manually".  When mdev is called from /sbin/hotplug in response to actual
kernel event, the path is like, for example,
"/sys/devices/pci0000:00/0000:00:11.0/host0/target0:0:0/0:0:0:0/bsg/0:0:0:0"
(actual example from my system).  Ie, it starts with something entirely
different.

According to the kernel, the only reliable way to get subsystem name is to
readlink("subsystem") in the device directory.  That did not exist in earlier
kernels (but it's not a recent addition either).

Most of the time it's ok to assume that pre-last component of the path actually
is the right thing, so it's ok to find pre-last slash on the pathname here.  It
will work on all cases which I have examples for (ie, on all my systems).

So instead of the above, searching backwards for pre-last slash seems to be a
good idea.  And ab-using 'path' variable is NOT a good idea, at least I don't
think it is :)

Thanks!


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