3.2-stable review patch. If anyone has any objections, please let me know.
------------------
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
commit 55ee64b30a38d688232e5eb2860467dddc493573 upstream.
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...
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Sakari Ailus <sakari.ailus@xxxxxx>
Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Cc: Archit Taneja <archit@xxxxxx>
Cc: Prabhakar Lad <prabhakar.lad@xxxxxx>
Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/drivers/media/video/omap/omap_vout.c
+++ b/drivers/media/video/omap/omap_vout.c
@@ -206,19 +206,21 @@ static u32 omap_vout_uservirt_to_phys(u3
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(¤t->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(¤t->mm->mmap_sem);
} else {
/* otherwise, use get_user_pages() for general userland pages */
int res, nr_pages = 1;
struct page *pages;
- down_read(¤t->mm->mmap_sem);
res = get_user_pages(current, current->mm, virtp, nr_pages, 1,
0, &pages, NULL);
--
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