[ 3.5.y.z extended stable ] Patch "omap_vout: find_vma() needs ->mmap_sem held" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    omap_vout: find_vma() needs ->mmap_sem held

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From cd668258395925e3b35853831a31e6392907532c Mon Sep 17 00:00:00 2001
From: Al Viro <viro at ZenIV.linux.org.uk>
Date: Sun, 16 Dec 2012 16:04:46 -0300
Subject: [PATCH] omap_vout: find_vma() needs ->mmap_sem held

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 at zeniv.linux.org.uk>
Cc: Sakari Ailus <sakari.ailus at iki.fi>
Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Cc: Archit Taneja <archit at ti.com>
Cc: Prabhakar Lad <prabhakar.lad at ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/media/video/omap/omap_vout.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/media/video/omap/omap_vout.c b/drivers/media/video/omap/omap_vout.c
index 88cf9d9..89f354e 100644
--- 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(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);
--
1.8.1.2