agp: fix OOM and buffer overflow

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>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c
index 012cba0d6d96..850a643ad694 100644
--- a/drivers/char/agp/generic.c
+++ b/drivers/char/agp/generic.c
@@ -115,6 +115,9 @@ 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;
@@ -234,11 +237,14 @@ 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) {