[34-longterm 225/247] agp: fix arbitrary kernel memory writes

Paul Gortmaker
2011-06-23T17:42:46Z

From: Vasiliy Kulikov <segoon@openwall.com>

-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.
-------------------

commit 194b3da873fd334ef183806db751473512af29ce upstream.

pg_start is copied from userspace on AGPIOC_BIND and AGPIOC_UNBIND ioctl
cmds of agp_ioctl() and passed to agpioc_bind_wrap(). As said in the
comment, (pg_start + mem->page_count) may wrap in case of AGPIOC_BIND,
and it is not checked at all in case of AGPIOC_UNBIND. As a result, user
with sufficient privileges (usually "video" group) may generate either
local DoS or privilege escalation.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
drivers/char/agp/generic.c | 11 ++++++++---
1 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c
index fb86708..13a3446 100644
--- a/drivers/char/agp/generic.c
+++ b/drivers/char/agp/generic.c
@@ -1124,8 +1124,8 @@ int agp_generic_insert_memory(struct agp_memory * mem, off_t pg_start, int type)
return -EINVAL;
}

- /* AK: could wrap */
- if ((pg_start + mem->page_count) > num_entries)
+ if (((pg_start + mem->page_count) > num_entries) ||
+ ((pg_start + mem->page_count) < pg_start))
return -EINVAL;

j = pg_start;
@@ -1159,7 +1159,7 @@ int agp_generic_remove_memory(struct agp_memory *mem, off_t pg_start, int type)
{
size_t i;
struct agp_bridge_data *bridge;
- int mask_type;
+ int mask_type, num_entries;

bridge = mem->bridge;
if (!bridge)
@@ -1171,6 +1171,11 @@ int agp_generic_remove_memory(struct agp_memory *mem, off_t pg_start, int type)
if (type != mem->type)
return -EINVAL;

+ num_entries = agp_num_entries();
+ if (((pg_start + mem->page_count) > num_entries) ||
+ ((pg_start + mem->page_count) < pg_start))
+ return -EINVAL;
+
mask_type = bridge->driver->agp_type_to_mask_type(bridge, type);
if (mask_type != 0) {
/* The generic routines know nothing of memory types */
--
1.7.4.4