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    Subject[PATCH 5.6 137/194] USB: usbfs: fix mmap dma mismatch
    Date
    From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    commit a0e710a7def471b8eb779ff551fc27701da49599 upstream.

    In commit 2bef9aed6f0e ("usb: usbfs: correct kernel->user page attribute
    mismatch") we switched from always calling remap_pfn_range() to call
    dma_mmap_coherent() to handle issues with systems with non-coherent USB host
    controller drivers. Unfortunatly, as syzbot quickly told us, not all the world
    is host controllers with DMA support, so we need to check what host controller
    we are attempting to talk to before doing this type of allocation.

    Thanks to Christoph for the quick idea of how to fix this.

    Fixes: 2bef9aed6f0e ("usb: usbfs: correct kernel->user page attribute mismatch")
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Hillf Danton <hdanton@sina.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Jeremy Linton <jeremy.linton@arm.com>
    Cc: stable <stable@vger.kernel.org>
    Reported-by: syzbot+353be47c9ce21b68b7ed@syzkaller.appspotmail.com
    Reviewed-by: Jeremy Linton <jeremy.linton@arm.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Link: https://lore.kernel.org/r/20200514112711.1858252-1-gregkh@linuxfoundation.org
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/usb/core/devio.c | 16 +++++++++++++---
    1 file changed, 13 insertions(+), 3 deletions(-)

    --- a/drivers/usb/core/devio.c
    +++ b/drivers/usb/core/devio.c
    @@ -251,9 +251,19 @@ static int usbdev_mmap(struct file *file
    usbm->vma_use_count = 1;
    INIT_LIST_HEAD(&usbm->memlist);

    - if (dma_mmap_coherent(hcd->self.sysdev, vma, mem, dma_handle, size)) {
    - dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
    - return -EAGAIN;
    + if (hcd->localmem_pool || !hcd_uses_dma(hcd)) {
    + if (remap_pfn_range(vma, vma->vm_start,
    + virt_to_phys(usbm->mem) >> PAGE_SHIFT,
    + size, vma->vm_page_prot) < 0) {
    + dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
    + return -EAGAIN;
    + }
    + } else {
    + if (dma_mmap_coherent(hcd->self.sysdev, vma, mem, dma_handle,
    + size)) {
    + dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
    + return -EAGAIN;
    + }
    }

    vma->vm_flags |= VM_IO;

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