On 09/07/18 07:22, Thierry Reding wrote:
> From: Thierry Reding <treding@xxxxxxxxxx>
>
> The kernel's vsnprintf() implementation discards all alpha-numeric
> characters following a %p conversion specifier. This is done in order to
> generically skip any of the various modifiers that the kernel supports.
> Unfortunately, the OF modalias is generated with a format string that
> violates the assumption made by vsnprintf():
>
> of:N%pOFnT%s
>
> While processing the above format string, vsnprintf() will eat the 'T'
> character, assuming that it belongs to the preceeding %p specifier. This
> results in a modalias with an incompatible format, which in turn causes
> the automatic loading of drivers based on modalias to no longer work.
>
> To fix this, split up the generation of the name & type fields into two
> separate snprintf() calls to avoid confusing the parser.
>
> Fixes: 73813f8483b1 ("of: Convert to using %pOFn instead of device_node.name")
> Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
> ---
> Note that a more elegant fix would be to make the %p format specifier
> parser report back the exact number of characters consumed. I briefly
> tried to implement it, but quickly ran into numerous special cases
> that make this solution rather involved.
>
> I can spend some more time to improve this in general if that's what we
> ultimately want, but I think this patch is a better short-term fix to
> workaround the issue.
> ---
> drivers/of/device.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/of/device.c b/drivers/of/device.c
> index daa075d87317..dabef9fc8538 100644
> --- a/drivers/of/device.c
> +++ b/drivers/of/device.c
> @@ -218,14 +218,20 @@ static ssize_t of_device_get_modalias(struct device *dev, char *str, ssize_t len
> if ((!dev) || (!dev->of_node))
> return -ENODEV;
>
> - /* Name & Type */
> - csize = snprintf(str, len, "of:N%pOFnT%s", dev->of_node,
> - dev->of_node->type);
> + /* Name */
> + csize = snprintf(str, len, "of:N%pOFn", dev->of_node);
> tsize = csize;
> len -= csize;
> if (str)
> str += csize;
>
> + /* Type */
> + csize = snprintf(str, len, "T%s", dev->of_node->type);
> + tsize += csize;
> + len -= csize;
> + if (str)
> + str += csize;
> +
> of_property_for_each_string(dev->of_node, "compatible", p, compat) {
> csize = strlen(compat) + 1;
> tsize += csize;
>
Reviewed-by: Frank Rowand <frank.rowand@xxxxxxxx>
