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Old 12-08-2009, 04:31 PM
Stefan Bader
 
Default drm/i915: Avoid NULL dereference with component_only tv_modes

Steve Conklin wrote:
> SRU Justification: This patch fixes a regression that has
> caused problems for users of another distribution. We
> probably have users experiencing the same problem.
>
> The patch is sane and minimal. The patch is in drm-next,
> but not yet in Linus's tree or stable.
>
> Bug #494045
>
> ----------------
>
> From d271817baecbccb47da0d9f28c285a0dae8a06b7 Mon Sep 17 00:00:00 2001
> From: Chris Wilson <chris@chris-wilson.co.uk>
> Date: Fri, 27 Nov 2009 13:06:56 +0000
> Subject: [PATCH] drm/i915: Avoid NULL dereference with component_only tv_modes
>
> In commit d2d9f2324, the guard for a valid video mode was removed. This
> caused the regression:
>
> kernel crash during kms graphic boot on Intel GM4500 platform
> https://bugzilla.redhat.com/show_bug.cgi?id=540218
>
> This patches changes the logic slightly not to rely on a coupled
> variable, but to just check whether the video_modes is valid before
> dereferencing.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: David Woodhouse <dwmw2@infradead.org>
> Cc: Zhenyu Wang <zhenyu.z.wang@intel.com>
> [ickle: Actually reference the correct bug report]
> Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>
> Signed-off-by: Eric Anholt <eric@anholt.net>
> ---
> drivers/gpu/drm/i915/intel_tv.c | 11 ++++-------
> 1 files changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
> index a0e4bc4..d7465ca 100644
> --- a/drivers/gpu/drm/i915/intel_tv.c
> +++ b/drivers/gpu/drm/i915/intel_tv.c
> @@ -1213,20 +1213,17 @@ intel_tv_mode_set(struct drm_encoder *encoder, struct drm_display_mode *mode,
> tv_ctl |= TV_TRILEVEL_SYNC;
> if (tv_mode->pal_burst)
> tv_ctl |= TV_PAL_BURST;
> +
> scctl1 = 0;
> - /* dda1 implies valid video levels */
> - if (tv_mode->dda1_inc) {
> + if (tv_mode->dda1_inc)
> scctl1 |= TV_SC_DDA1_EN;
> - }
> -
> if (tv_mode->dda2_inc)
> scctl1 |= TV_SC_DDA2_EN;
> -
> if (tv_mode->dda3_inc)
> scctl1 |= TV_SC_DDA3_EN;
> -
> scctl1 |= tv_mode->sc_reset;
> - scctl1 |= video_levels->burst << TV_BURST_LEVEL_SHIFT;
> + if (video_levels)
> + scctl1 |= video_levels->burst << TV_BURST_LEVEL_SHIFT;
> scctl1 |= tv_mode->dda1_inc << TV_SCDDA1_INC_SHIFT;
>
> scctl2 = tv_mode->dda2_size << TV_SCDDA2_SIZE_SHIFT |

My preference would also be to get this over to upstream+stable
(with or without the cosmetically change) and then back to us.
Seems there is at least one more Karmic update after 2.6.31.7
from what I read from Greg's comments.

-Stefan

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