[CVE-2018-8781][T/A][SRU][PATCH 1/1] drm: udl: Properly check framebuffer mmap offsets

[Po-Hsu Lin]

From: Greg Kroah-Hartman <gregkh at linuxfoundation.org>

CVE-2018-8781

The memmap options sent to the udl framebuffer driver were not being
checked for all sets of possible crazy values.  Fix this up by properly
bounding the allowed values.

Reported-by: Eyal Itkin <eyalit at checkpoint.com>
Cc: stable <stable at vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180321154553.GA18454@kroah.com
(cherry picked from commit 3b82a4db8eaccce735dffd50b4d4e1578099b8e8)
Signed-off-by: Po-Hsu Lin <po-hsu.lin at canonical.com>
---
 drivers/gpu/drm/udl/udl_fb.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/udl/udl_fb.c b/drivers/gpu/drm/udl/udl_fb.c
index 4a65003..f8c0997 100644
--- a/drivers/gpu/drm/udl/udl_fb.c
+++ b/drivers/gpu/drm/udl/udl_fb.c
@@ -158,10 +158,15 @@ static int udl_fb_mmap(struct fb_info *info, struct vm_area_struct *vma)
 {
 	unsigned long start = vma->vm_start;
 	unsigned long size = vma->vm_end - vma->vm_start;
-	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
+	unsigned long offset;
 	unsigned long page, pos;
 
-	if (offset + size > info->fix.smem_len)
+	if (vma->vm_pgoff > (~0UL >> PAGE_SHIFT))
+		return -EINVAL;
+
+	offset = vma->vm_pgoff << PAGE_SHIFT;
+
+	if (offset > info->fix.smem_len || size > info->fix.smem_len - offset)
 		return -EINVAL;
 
 	pos = (unsigned long)info->fix.smem_start + offset;
-- 
2.7.4