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fbdev: color map copying bounds checking

commit 2dc705a9930b4806250fbf5a76e55266e59389f2 upstream.

Copying color maps to userspace doesn't check the value of to->start,
which will cause kernel heap buffer OOB read due to signedness wraps.

CVE-2016-8405

Change-Id: I6411ce16a58744bd280741386354b921de591606
Link: http://lkml.kernel.org/r/20170105224249.GA50925@beast
Fixes: 1da177e ("Linux-2.6.12-rc2")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Peter Pi (@heisecode) of Trend Micro
Cc: Min Chong <mchong@google.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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kees authored and andi34 committed Jan 24, 2017
1 parent c4eab28 commit a1697c710fd7df6cf9d22dca011af2e74a5b15bf
Showing with 14 additions and 12 deletions.
  1. +14 −12 drivers/video/fbcmap.c
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@@ -163,17 +163,18 @@ void fb_dealloc_cmap(struct fb_cmap *cmap)
int fb_copy_cmap(const struct fb_cmap *from, struct fb_cmap *to)
{
int tooff = 0, fromoff = 0;
int size;
unsigned int tooff = 0, fromoff = 0;
size_t size;
if (to->start > from->start)
fromoff = to->start - from->start;
else
tooff = from->start - to->start;
size = to->len - tooff;
if (size > (int) (from->len - fromoff))
size = from->len - fromoff;
if (size <= 0)
if (fromoff >= from->len || tooff >= to->len)
return -EINVAL;
size = min_t(size_t, to->len - tooff, from->len - fromoff);
if (size == 0)
return -EINVAL;
size *= sizeof(u16);
@@ -187,17 +188,18 @@ int fb_copy_cmap(const struct fb_cmap *from, struct fb_cmap *to)
int fb_cmap_to_user(const struct fb_cmap *from, struct fb_cmap_user *to)
{
int tooff = 0, fromoff = 0;
int size;
unsigned int tooff = 0, fromoff = 0;
size_t size;
if (to->start > from->start)
fromoff = to->start - from->start;
else
tooff = from->start - to->start;
size = to->len - tooff;
if (size > (int) (from->len - fromoff))
size = from->len - fromoff;
if (size <= 0)
if (fromoff >= from->len || tooff >= to->len)
return -EINVAL;
size = min_t(size_t, to->len - tooff, from->len - fromoff);
if (size == 0)
return -EINVAL;
size *= sizeof(u16);

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