On 03/10/17 16:51, Linus Walleij wrote:
> I forgot to account for the fact that the device core holds a
> reference to a device added with device_initialize() that need
> to be released with a corresponding put_device() to reach a 0
> refcount at the end of the lifecycle.
>
> This led to a NULL pointer reference when freeing the device
> when e.g. unbidning the host device in sysfs.
>
> Fix this and use the device .release() callback to free the
> IDA and free:ing the memory used by the RPMB device.
>
> Before this patch:
>
> /sys/bus/amba/drivers/mmci-pl18x$ echo 80114000.sdi4_per2 > unbind
> [ 29.797332] mmc3: card 0001 removed
> [ 29.810791] Unable to handle kernel NULL pointer dereference at
> virtual address 00000050
> [ 29.818878] pgd = de70c000
> [ 29.821624] [00000050] *pgd=1e70a831, *pte=00000000, *ppte=00000000
> [ 29.827911] Internal error: Oops: 17 [#1] PREEMPT SMP ARM
> [ 29.833282] Modules linked in:
> [ 29.836334] CPU: 1 PID: 154 Comm: sh Not tainted
> 4.14.0-rc3-00039-g83318e309566-dirty #736
> [ 29.844604] Hardware name: ST-Ericsson Ux5x0 platform (Device Tree Support)
> [ 29.851562] task: de572700 task.stack: de742000
> [ 29.856079] PC is at kernfs_find_ns+0x8/0x100
> [ 29.860443] LR is at kernfs_find_and_get_ns+0x30/0x48
>
> After this patch:
>
> /sys/bus/amba/drivers/mmci-pl18x$ echo 80005000.sdi4_per2 > unbind
> [ 20.623382] mmc3: card 0001 removed
>
> Fixes: 0ab0c7c0e65a ("mmc: block: Convert RPMB to a character device")
> Reported-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
> ChangeLog v2->v3:
> - Fix the block device reference counting: instead of manipulating
> md->usage directly, call the proper refcounting functions
> mmc_blk_get() and mmc_blk_put().
> ChangeLog v1->v2:
> - Drop the print from removing the RPMB partition
> - Refactor the error path of the RPMB to use refcounting
> - Drop the verbose comment on refcounts
> ---
> drivers/mmc/core/block.c | 28 ++++++++++++++++++----------
> 1 file changed, 18 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
> index c29dbcec7c61..46ecbaec8035 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -2299,7 +2299,7 @@ static int mmc_rpmb_chrdev_open(struct inode *inode, struct file *filp)
> get_device(&rpmb->dev);
> filp->private_data = rpmb;
> mutex_lock(&open_lock);
> - rpmb->md->usage++;
> + mmc_blk_get(rpmb->md->disk);
mmc_blk_get() also tries to mutex_lock(&open_lock)
But how do you know md still exists? Looks like you need
to make the disk the parent of the rpmb device and then
use the disk to get a reference to md.
Another thing that looks odd: mmc_blk_ioctl() checks for
capable(CAP_SYS_RAWIO) but mmc_rpmb_ioctl() does not.
Is that intentional?
> mutex_unlock(&open_lock);
>
> return nonseekable_open(inode, filp);
> @@ -2312,7 +2312,7 @@ static int mmc_rpmb_chrdev_release(struct inode *inode, struct file *filp)
>
> put_device(&rpmb->dev);
> mutex_lock(&open_lock);
> - rpmb->md->usage--;
> + mmc_blk_put(rpmb->md);
> mutex_unlock(&open_lock);
>
> return 0;
> @@ -2329,6 +2329,13 @@ static const struct file_operations mmc_rpmb_fileops = {
> #endif
> };
>
> +static void mmc_blk_rpmb_device_release(struct device *dev)
> +{
> + struct mmc_rpmb_data *rpmb = dev_get_drvdata(dev);
> +
> + ida_simple_remove(&mmc_rpmb_ida, rpmb->id);
> + kfree(rpmb);
> +}
>
> static int mmc_blk_alloc_rpmb_part(struct mmc_card *card,
> struct mmc_blk_data *md,
> @@ -2347,8 +2354,10 @@ static int mmc_blk_alloc_rpmb_part(struct mmc_card *card,
> return devidx;
>
> rpmb = kzalloc(sizeof(*rpmb), GFP_KERNEL);
> - if (!rpmb)
> + if (!rpmb) {
> + ida_simple_remove(&mmc_rpmb_ida, devidx);
> return -ENOMEM;
> + }
>
> snprintf(rpmb_name, sizeof(rpmb_name),
> "mmcblk%u%s", card->host->index, subname ? subname : "");
> @@ -2359,6 +2368,7 @@ static int mmc_blk_alloc_rpmb_part(struct mmc_card *card,
> rpmb->dev.bus = &mmc_rpmb_bus_type;
> rpmb->dev.devt = MKDEV(MAJOR(mmc_rpmb_devt), rpmb->id);
> rpmb->dev.parent = &card->dev;
> + rpmb->dev.release = mmc_blk_rpmb_device_release;
> device_initialize(&rpmb->dev);
> dev_set_drvdata(&rpmb->dev, rpmb);
> rpmb->md = md;
> @@ -2368,7 +2378,7 @@ static int mmc_blk_alloc_rpmb_part(struct mmc_card *card,
> ret = cdev_device_add(&rpmb->chrdev, &rpmb->dev);
> if (ret) {
> pr_err("%s: could not add character device\n", rpmb_name);
> - goto out_remove_ida;
> + goto out_put_device;
> }
>
> list_add(&rpmb->node, &md->rpmbs);
> @@ -2383,18 +2393,16 @@ static int mmc_blk_alloc_rpmb_part(struct mmc_card *card,
>
> return 0;
>
> -out_remove_ida:
> - ida_simple_remove(&mmc_rpmb_ida, rpmb->id);
> - kfree(rpmb);
> +out_put_device:
> + put_device(&rpmb->dev);
> return ret;
> }
>
> static void mmc_blk_remove_rpmb_part(struct mmc_rpmb_data *rpmb)
> +
> {
> cdev_device_del(&rpmb->chrdev, &rpmb->dev);
> - device_del(&rpmb->dev);
> - ida_simple_remove(&mmc_rpmb_ida, rpmb->id);
> - kfree(rpmb);
> + put_device(&rpmb->dev);
> }
>
> /* MMC Physical partitions consist of two boot partitions and
>
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