agp: fix arbitrary kernel memory writes

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>

diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c
index 850a643..b072648 100644 (file)
--- a/drivers/char/agp/generic.c
+++ b/drivers/char/agp/generic.c
@@ -1095,8 +1095,8 @@ 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;
@@ -1130,7 +1130,7 @@ 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)
@@ -1142,6 +1142,11 @@ 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 */