drm/i915: Prevent overflow of execbuf.buffer_count and num_cliprects

We check whether the multiplies will overflow prior to calling
kmalloc_array so that we can respond with -EINVAL for the invalid user
arguments rather than treating it as an -ENOMEM that would otherwise
occur. However, as Dan Carpenter pointed out, we did an addition on the
unsigned int prior to passing to kmalloc_array where it would be
promoted to size_t for the calculation, thereby allowing it to overflow
and underallocate.

v2: buffer_count is currently limited to INT_MAX because we treat it as
signaled variable for LUT_HANDLE in eb_lookup_vma
v3: Move common checks for eb1/eb2 into the same function
v4: Put the check back for nfence*sizeof(user_fence) overflow
v5: access_ok uses ULONG_MAX but kvmalloc_array uses SIZE_MAX
v6: size_t and unsigned long are not type-equivalent on 32b

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171116105059.25142-1-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 435ed95..53ccb27 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -2074,23 +2074,27 @@ static struct drm_syncobj **
 get_fence_array(struct drm_i915_gem_execbuffer2 *args,
                struct drm_file *file)
 {
-       const unsigned int nfences = args->num_cliprects;
+       const unsigned long nfences = args->num_cliprects;
        struct drm_i915_gem_exec_fence __user *user;
        struct drm_syncobj **fences;
-       unsigned int n;
+       unsigned long n;
        int err;
 
        if (!(args->flags & I915_EXEC_FENCE_ARRAY))
                return NULL;
 
-       if (nfences > SIZE_MAX / sizeof(*fences))
+       /* Check multiplication overflow for access_ok() and kvmalloc_array() */
+       BUILD_BUG_ON(sizeof(size_t) > sizeof(unsigned long));
+       if (nfences > min_t(unsigned long,
+                           ULONG_MAX / sizeof(*user),
+                           SIZE_MAX / sizeof(*fences)))
                return ERR_PTR(-EINVAL);
 
        user = u64_to_user_ptr(args->cliprects_ptr);
-       if (!access_ok(VERIFY_READ, user, nfences * 2 * sizeof(u32)))
+       if (!access_ok(VERIFY_READ, user, nfences * sizeof(*user)))
                return ERR_PTR(-EFAULT);
 
-       fences = kvmalloc_array(args->num_cliprects, sizeof(*fences),
+       fences = kvmalloc_array(nfences, sizeof(*fences),
                                __GFP_NOWARN | GFP_KERNEL);
        if (!fences)
                return ERR_PTR(-ENOMEM);
@@ -2447,6 +2451,26 @@ err_in_fence:
        return err;
 }
 
+static size_t eb_element_size(void)
+{
+       return (sizeof(struct drm_i915_gem_exec_object2) +
+               sizeof(struct i915_vma *) +
+               sizeof(unsigned int));
+}
+
+static bool check_buffer_count(size_t count)
+{
+       const size_t sz = eb_element_size();
+
+       /*
+        * When using LUT_HANDLE, we impose a limit of INT_MAX for the lookup
+        * array size (see eb_create()). Otherwise, we can accept an array as
+        * large as can be addressed (though use large arrays at your peril)!
+        */
+
+       return !(count < 1 || count > INT_MAX || count > SIZE_MAX / sz - 1);
+}
+
 /*
  * Legacy execbuffer just creates an exec2 list from the original exec object
  * list array and passes it to the real function.
@@ -2455,18 +2479,16 @@ int
 i915_gem_execbuffer(struct drm_device *dev, void *data,
                    struct drm_file *file)
 {
-       const size_t sz = (sizeof(struct drm_i915_gem_exec_object2) +
-                          sizeof(struct i915_vma *) +
-                          sizeof(unsigned int));
        struct drm_i915_gem_execbuffer *args = data;
        struct drm_i915_gem_execbuffer2 exec2;
        struct drm_i915_gem_exec_object *exec_list = NULL;
        struct drm_i915_gem_exec_object2 *exec2_list = NULL;
+       const size_t count = args->buffer_count;
        unsigned int i;
        int err;
 
-       if (args->buffer_count < 1 || args->buffer_count > SIZE_MAX / sz - 1) {
-               DRM_DEBUG("execbuf2 with %d buffers\n", args->buffer_count);
+       if (!check_buffer_count(count)) {
+               DRM_DEBUG("execbuf2 with %zd buffers\n", count);
                return -EINVAL;
        }
 
@@ -2485,9 +2507,9 @@ i915_gem_execbuffer(struct drm_device *dev, void *data,
                return -EINVAL;
 
        /* Copy in the exec list from userland */
-       exec_list = kvmalloc_array(args->buffer_count, sizeof(*exec_list),
+       exec_list = kvmalloc_array(count, sizeof(*exec_list),
                                   __GFP_NOWARN | GFP_KERNEL);
-       exec2_list = kvmalloc_array(args->buffer_count + 1, sz,
+       exec2_list = kvmalloc_array(count + 1, eb_element_size(),
                                    __GFP_NOWARN | GFP_KERNEL);
        if (exec_list == NULL || exec2_list == NULL) {
                DRM_DEBUG("Failed to allocate exec list for %d buffers\n",
@@ -2498,7 +2520,7 @@ i915_gem_execbuffer(struct drm_device *dev, void *data,
        }
        err = copy_from_user(exec_list,
                             u64_to_user_ptr(args->buffers_ptr),
-                            sizeof(*exec_list) * args->buffer_count);
+                            sizeof(*exec_list) * count);
        if (err) {
                DRM_DEBUG("copy %d exec entries failed %d\n",
                          args->buffer_count, err);
@@ -2548,16 +2570,14 @@ int
 i915_gem_execbuffer2(struct drm_device *dev, void *data,
                     struct drm_file *file)
 {
-       const size_t sz = (sizeof(struct drm_i915_gem_exec_object2) +
-                          sizeof(struct i915_vma *) +
-                          sizeof(unsigned int));
        struct drm_i915_gem_execbuffer2 *args = data;
        struct drm_i915_gem_exec_object2 *exec2_list;
        struct drm_syncobj **fences = NULL;
+       const size_t count = args->buffer_count;
        int err;
 
-       if (args->buffer_count < 1 || args->buffer_count > SIZE_MAX / sz - 1) {
-               DRM_DEBUG("execbuf2 with %d buffers\n", args->buffer_count);
+       if (!check_buffer_count(count)) {
+               DRM_DEBUG("execbuf2 with %zd buffers\n", count);
                return -EINVAL;
        }
 
@@ -2565,17 +2585,17 @@ i915_gem_execbuffer2(struct drm_device *dev, void *data,
                return -EINVAL;
 
        /* Allocate an extra slot for use by the command parser */
-       exec2_list = kvmalloc_array(args->buffer_count + 1, sz,
+       exec2_list = kvmalloc_array(count + 1, eb_element_size(),
                                    __GFP_NOWARN | GFP_KERNEL);
        if (exec2_list == NULL) {
-               DRM_DEBUG("Failed to allocate exec list for %d buffers\n",
-                         args->buffer_count);
+               DRM_DEBUG("Failed to allocate exec list for %zd buffers\n",
+                         count);
                return -ENOMEM;
        }
        if (copy_from_user(exec2_list,
                           u64_to_user_ptr(args->buffers_ptr),
-                          sizeof(*exec2_list) * args->buffer_count)) {
-               DRM_DEBUG("copy %d exec entries failed\n", args->buffer_count);
+                          sizeof(*exec2_list) * count)) {
+               DRM_DEBUG("copy %zd exec entries failed\n", count);
                kvfree(exec2_list);
                return -EFAULT;
        }