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    SubjectRe: [PATCH -next] spi: Fix double IDR allocation with DT aliases
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    Hi Geert

    Thank you for keeping me informed.

    I have to point at the following threat: a dynamically allocated ID may
    'squat' a bus ID that intended for a device with statically allocated
    ID. This scenario is possible since module loading order is uncertain.
    This threat seems to be inevitable...

    --
    Best regards,
    Kirill.


    On 08/21/2018 12:53 PM, Geert Uytterhoeven wrote:
    > If the SPI bus number is provided by a DT alias, idr_alloc() is called
    > twice, leading to:
    >
    > WARNING: CPU: 1 PID: 1 at drivers/spi/spi.c:2179 spi_register_controller+0x11c/0x5d8
    > couldn't get idr
    >
    > Fix this by moving the handling of fixed SPI bus numbers up, before the
    > DT handling code fills in ctlr->bus_num.
    >
    > Fixes: 1a4327fbf4554d5b ("spi: fix IDR collision on systems with both fixed and dynamic SPI bus numbers")
    > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
    > ---
    > Seen on e.g. r8a7791/koelsch, breaking both RSPI and MSIOF.
    > ---
    > drivers/spi/spi.c | 22 +++++++++++-----------
    > 1 file changed, 11 insertions(+), 11 deletions(-)
    >
    > diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
    > index a00d006d4c3a1c5a..9da0bc5a036cfff6 100644
    > --- a/drivers/spi/spi.c
    > +++ b/drivers/spi/spi.c
    > @@ -2143,8 +2143,17 @@ int spi_register_controller(struct spi_controller *ctlr)
    > */
    > if (ctlr->num_chipselect == 0)
    > return -EINVAL;
    > - /* allocate dynamic bus number using Linux idr */
    > - if ((ctlr->bus_num < 0) && ctlr->dev.of_node) {
    > + if (ctlr->bus_num >= 0) {
    > + /* devices with a fixed bus num must check-in with the num */
    > + mutex_lock(&board_lock);
    > + id = idr_alloc(&spi_master_idr, ctlr, ctlr->bus_num,
    > + ctlr->bus_num + 1, GFP_KERNEL);
    > + mutex_unlock(&board_lock);
    > + if (WARN(id < 0, "couldn't get idr"))
    > + return id == -ENOSPC ? -EBUSY : id;
    > + ctlr->bus_num = id;
    > + } else if (ctlr->dev.of_node) {
    > + /* allocate dynamic bus number using Linux idr */
    > id = of_alias_get_id(ctlr->dev.of_node, "spi");
    > if (id >= 0) {
    > ctlr->bus_num = id;
    > @@ -2170,15 +2179,6 @@ int spi_register_controller(struct spi_controller *ctlr)
    > if (WARN(id < 0, "couldn't get idr"))
    > return id;
    > ctlr->bus_num = id;
    > - } else {
    > - /* devices with a fixed bus num must check-in with the num */
    > - mutex_lock(&board_lock);
    > - id = idr_alloc(&spi_master_idr, ctlr, ctlr->bus_num,
    > - ctlr->bus_num + 1, GFP_KERNEL);
    > - mutex_unlock(&board_lock);
    > - if (WARN(id < 0, "couldn't get idr"))
    > - return id == -ENOSPC ? -EBUSY : id;
    > - ctlr->bus_num = id;
    > }
    > INIT_LIST_HEAD(&ctlr->queue);
    > spin_lock_init(&ctlr->queue_lock);
    >


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