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>

diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c
index 012cba0..850a643 100644 (file)
--- 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) {