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[media] omap_vout: find_vma() needs ->mmap_sem held

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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).

While we are at it, what prevents VIDIOC_PREPARE_BUF calling
v4l_prepare_buf() -> (e.g) vb2_ioctl_prepare_buf() -> vb2_prepare_buf() ->
__buf_prepare() -> __qbuf_userptr() -> vb2_vmalloc_get_userptr() -> find_vma(),
AFAICS without having taken ->mmap_sem anywhere in process?  The code flow
is bloody convoluted and depends on a bunch of things done by initialization,
so I certainly might've missed something...

Cc: stable@vger.kernel.org [2.6.35]
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Sakari Ailus <sakari.ailus@iki.fi>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Archit Taneja <archit@ti.com>
Cc: Prabhakar Lad <prabhakar.lad@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Al Viro 2012-12-16 16:04:46 -03:00 committed by Mauro Carvalho Chehab
parent a0a030bdbe
commit 55ee64b30a
1 changed files with 7 additions and 5 deletions
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12
drivers/media/platform/omap/omap_vout.c
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@ -205,19 +205,21 @@ 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);
} else if (vma && (vma->vm_flags & VM_IO) && vma->vm_pgoff) {
if (virtp >= PAGE_OFFSET)
return virt_to_phys((void *) virtp);
down_read(&current->mm->mmap_sem);
vma = find_vma(mm, virtp);
if (vma && (vma->vm_flags & VM_IO) && vma->vm_pgoff) {
/* 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);