lkml.org 
[lkml]   [2019]   [Mar]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 1/4] leds: netdev trigger: use memcpy in device_name_store
    Hi!

    > If userspace doesn't end the input with a newline (which can easily
    > happen if the write happens from a C program that does write(fd,
    > iface, strlen(iface))), we may end up including garbage from a
    > previous, longer value in the device_name. For example
    >
    > # cat device_name
    >
    > # printf 'eth12' > device_name
    > # cat device_name
    > eth12
    > # printf 'eth3' > device_name
    > # cat device_name
    > eth32
    >
    > I highly doubt anybody is relying on this behaviour, so switch to
    > simply copying the bytes (we've already checked that size is <
    > IFNAMSIZ) and unconditionally zero-terminate it; of course, we also
    > still have to strip a trailing newline.

    char device_name[IFNAMSIZ];

    Ok, good catch reporting the bug, but are you sure the fix is right?

    AFAICT the design is that device_name does _not_ have to be zero
    terminated, and your fix incorrectly limits the size of device_name.

    Pavel

    > index 3dd3ed46d473..ddc2b90ad7ec 100644
    > --- a/drivers/leds/trigger/ledtrig-netdev.c
    > +++ b/drivers/leds/trigger/ledtrig-netdev.c
    > @@ -122,7 +122,8 @@ static ssize_t device_name_store(struct device *dev,
    > trigger_data->net_dev = NULL;
    > }
    >
    > - strncpy(trigger_data->device_name, buf, size);
    > + memcpy(trigger_data->device_name, buf, size);
    > + trigger_data->device_name[size] = '\0';

    I'd do = 0 for consistency with code below.

    I believe the strncpy() is right to use here, but code should be
    modified so that zero-termination is not required.

    > if (size > 0 && trigger_data->device_name[size - 1] == '\n')
    > trigger_data->device_name[size - 1] = 0;
    >
    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
    [unhandled content-type:application/pgp-signature]
    \
     
     \ /
      Last update: 2019-03-14 11:14    [W:2.273 / U:0.128 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site