If command buffer claims a number of words that is higher than its BO can
fit and a relocation lays past the BO, a kernel OOPS will be fired on that
relocation address patching. This was triggered by an opentegra Xorg driver
that erroneously pushed too many commands to the pushbuf.

[   46.829393] Unable to handle kernel paging request at virtual address 
f09b2000
...
[<c04a3ba4>] (host1x_job_pin) from [<c04dfcd0>] (tegra_drm_submit+0x474/0x510)
[<c04dfcd0>] (tegra_drm_submit) from [<c04deea0>] (tegra_submit+0x50/0x6c)
[<c04deea0>] (tegra_submit) from [<c04c07c0>] (drm_ioctl+0x1e4/0x3ec)
[<c04c07c0>] (drm_ioctl) from [<c02541a0>] (do_vfs_ioctl+0x9c/0x8e4)
[<c02541a0>] (do_vfs_ioctl) from [<c0254a1c>] (SyS_ioctl+0x34/0x5c)
[<c0254a1c>] (SyS_ioctl) from [<c0107640>] (ret_fast_syscall+0x0/0x3c)

Signed-off-by: Dmitry Osipenko <dig...@gmail.com>
---

v2: Take into account the cmdbuf.offset

 drivers/gpu/drm/tegra/drm.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
index 732c8d98044f..9ad4ac7c08d1 100644
--- a/drivers/gpu/drm/tegra/drm.c
+++ b/drivers/gpu/drm/tegra/drm.c
@@ -361,20 +361,30 @@ int tegra_drm_submit(struct tegra_drm_context *context,
 
        while (num_cmdbufs) {
                struct drm_tegra_cmdbuf cmdbuf;
-               struct host1x_bo *bo;
+               struct drm_gem_object *gem;
+               struct tegra_bo *bo;
 
                if (copy_from_user(&cmdbuf, cmdbufs, sizeof(cmdbuf))) {
                        err = -EFAULT;
                        goto fail;
                }
 
-               bo = host1x_bo_lookup(file, cmdbuf.handle);
-               if (!bo) {
+               gem = drm_gem_object_lookup(file, cmdbuf.handle);
+               if (!gem) {
                        err = -ENOENT;
                        goto fail;
                }
 
-               host1x_job_add_gather(job, bo, cmdbuf.words, cmdbuf.offset);
+               drm_gem_object_unreference_unlocked(gem);
+
+               if (cmdbuf.offset + cmdbuf.words * 4 > gem->size) {
+                       err = -EINVAL;
+                       goto fail;
+               }
+
+               bo = to_tegra_bo(gem);
+               host1x_job_add_gather(job, &bo->base,
+                                     cmdbuf.words, cmdbuf.offset);
                num_cmdbufs--;
                cmdbufs++;
        }
-- 
2.12.2

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