[34-longterm 226/247] agp: fix OOM and buffer overflow

Paul Gortmaker
2011-06-23T17:39:04Z

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 b522f02184b413955f3bc952e3776ce41edc6355 upstream.

page_count is copied from userspace. agp_allocate_memory() tries to
check whether this number is too big, but doesn't take into account the
wrap case. Also agp_create_user_memory() doesn't check whether
alloc_size is calculated from num_agp_pages variable without overflow.
This may lead to allocation of too small buffer with following buffer
overflow.

Another problem in agp code is not addressed in the patch - kernel memory
exhaustion (AGPIOC_RESERVE and AGPIOC_ALLOCATE ioctls). It is not checked
whether requested pid is a pid of the caller (no check in agpioc_reserve_wrap()).
Each allocation is limited to 16KB, though, there is no per-process limit.
This might lead to OOM situation, which is not even solved in case of the
caller death by OOM killer - the memory is allocated for another (faked) process.

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 | 8 +++++++-
1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c
index 13a3446..22b40c0 100644
--- a/drivers/char/agp/generic.c
+++ b/drivers/char/agp/generic.c
@@ -124,6 +124,9 @@ static struct agp_memory *agp_create_user_memory(unsigned long num_agp_pages)
struct agp_memory *new;
unsigned long alloc_size = num_agp_pages*sizeof(struct page *);

+ if (INT_MAX/sizeof(struct page *) < num_agp_pages)
+ return NULL;
+
new = kzalloc(sizeof(struct agp_memory), GFP_KERNEL);
if (new == NULL)
return NULL;
@@ -243,11 +246,14 @@ struct agp_memory *agp_allocate_memory(struct agp_bridge_data *bridge,
int scratch_pages;
struct agp_memory *new;
size_t i;
+ int cur_memory;

if (!bridge)
return NULL;

- if ((atomic_read(&bridge->current_memory_agp) + page_count) > bridge->max_memory_agp)
+ cur_memory = atomic_read(&bridge->current_memory_agp);
+ if ((cur_memory + page_count > bridge->max_memory_agp) ||
+ (cur_memory + page_count < page_count))
return NULL;

if (type >= AGP_USER_TYPES) {
--
1.7.4.4