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SubjectRe: [PATCH] omap_vout: find_vma() needs ->mmap_sem held
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On Sat, 2012-12-15 at 20:12 +0000, Al Viro wrote:
> Walking rbtree while it's modified is a Bad Idea(tm); besides,
> the result of find_vma() can be freed just as it's getting returned
> to caller. Fortunately, it's easy to fix - just take ->mmap_sem a bit
> earlier (and don't bother with find_vma() at all if virtp >= PAGE_OFFSET -
> in that case we don't even look at its result).
>
> Cc: stable@vger.kernel.org [2.6.35]
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> ---
> diff --git a/drivers/media/platform/omap/omap_vout.c b/drivers/media/platform/omap/omap_vout.c
> index 9935040..984512f 100644
> --- a/drivers/media/platform/omap/omap_vout.c
> +++ b/drivers/media/platform/omap/omap_vout.c
> @@ -207,19 +207,21 @@ static u32 omap_vout_uservirt_to_phys(u32 virtp)
> struct vm_area_struct *vma;
> struct mm_struct *mm = current->mm;
>
> - vma = find_vma(mm, virtp);
> /* For kernel direct-mapped memory, take the easy way */
> - if (virtp >= PAGE_OFFSET) {
> - physp = virt_to_phys((void *) virtp);
> + if (virtp >= PAGE_OFFSET)
> + return virt_to_phys((void *) virtp);
> +
> + down_read(&current->mm->mmap_sem);
> + vma = find_vma(mm, virtp);
> } else if (vma && (vma->vm_flags & VM_IO) && vma->vm_pgoff) {

Shouldn't that line become
if (vma && (vma->vm_flags & VM_IO) && vma->vm_pgoff) {

so that this actually compiles?

> /* this will catch, kernel-allocated, mmaped-to-usermode
> addresses */
> physp = (vma->vm_pgoff << PAGE_SHIFT) + (virtp - vma->vm_start);
> + up_read(&current->mm->mmap_sem);
> } else {
> /* otherwise, use get_user_pages() for general userland pages */
> int res, nr_pages = 1;
> struct page *pages;
> - down_read(&current->mm->mmap_sem);
>
> res = get_user_pages(current, current->mm, virtp, nr_pages, 1,
> 0, &pages, NULL);


Paul Bolle



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