[PATCH] [6/98] agp: fix OOM and buffer overflow

Andi Kleen
2011-07-27T00:41:45Z

From: Vasiliy Kulikov <segoon@openwall.com>

[ upstream commit b522f02184b413955f3bc952e3776ce41edc6355 ]

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: Andi Kleen <ak@linux.intel.com>

Index: linux-2.6.35.y/drivers/char/agp/generic.c
===================================================================
--- linux-2.6.35.y.orig/drivers/char/agp/generic.c
+++ linux-2.6.35.y/drivers/char/agp/generic.c
@@ -122,6 +122,9 @@ static struct agp_memory *agp_create_use
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;
@@ -241,11 +244,14 @@ struct agp_memory *agp_allocate_memory(s
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) {