| Message ID | 20211005192905.v2.1.Ib059f9c23c2611cb5a9d760e7d0a700c1295928d@changeid (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] drm/edid: In connector_bad_edid() cap num_of_ext by num_blocks read | expand |
Hi, On Tue, Oct 5, 2021 at 7:29 PM Douglas Anderson <dianders@chromium.org> wrote: > > In commit e11f5bd8228f ("drm: Add support for DP 1.4 Compliance edid > corruption test") the function connector_bad_edid() started assuming > that the memory for the EDID passed to it was big enough to hold > `edid[0x7e] + 1` blocks of data (1 extra for the base block). It > completely ignored the fact that the function was passed `num_blocks` > which indicated how much memory had been allocated for the EDID. > > Let's fix this by adding a bounds check. > > This is important for handling the case where there's an error in the > first block of the EDID. In that case we will call > connector_bad_edid() without having re-allocated memory based on > `edid[0x7e]`. > > Fixes: e11f5bd8228f ("drm: Add support for DP 1.4 Compliance edid corruption test") > Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com> > Signed-off-by: Douglas Anderson <dianders@chromium.org> > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> > --- > This problem report came up in the context of a patch I sent out [1] > and this is my attempt at a fix. The problem predates my patch, > though. I don't personally know anything about DP compliance testing > and what should be happening here, nor do I apparently have any > hardware that actually reports a bad EDID. Thus this is just compile > tested. I'm hoping that someone here can test this and make sure it > seems OK to them. > > Changes in v2: > - Added a comment/changed math to help make it easier to grok. > > drivers/gpu/drm/drm_edid.c | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) Pushed this to drm-misc-fixes since the commit it fixes is fairly old. fdc21c35aaa1 drm/edid: In connector_bad_edid() cap num_of_ext by num_blocks read -Doug
On Wed, Oct 06, 2021 at 03:45:07PM -0700, Doug Anderson wrote: > Hi, > > On Tue, Oct 5, 2021 at 7:29 PM Douglas Anderson <dianders@chromium.org> wrote: > > > > In commit e11f5bd8228f ("drm: Add support for DP 1.4 Compliance edid > > corruption test") the function connector_bad_edid() started assuming > > that the memory for the EDID passed to it was big enough to hold > > `edid[0x7e] + 1` blocks of data (1 extra for the base block). It > > completely ignored the fact that the function was passed `num_blocks` > > which indicated how much memory had been allocated for the EDID. > > > > Let's fix this by adding a bounds check. > > > > This is important for handling the case where there's an error in the > > first block of the EDID. In that case we will call > > connector_bad_edid() without having re-allocated memory based on > > `edid[0x7e]`. > > > > Fixes: e11f5bd8228f ("drm: Add support for DP 1.4 Compliance edid corruption test") > > Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com> > > Signed-off-by: Douglas Anderson <dianders@chromium.org> > > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> > > --- > > This problem report came up in the context of a patch I sent out [1] > > and this is my attempt at a fix. The problem predates my patch, > > though. I don't personally know anything about DP compliance testing > > and what should be happening here, nor do I apparently have any > > hardware that actually reports a bad EDID. Thus this is just compile > > tested. I'm hoping that someone here can test this and make sure it > > seems OK to them. > > > > Changes in v2: > > - Added a comment/changed math to help make it easier to grok. > > > > drivers/gpu/drm/drm_edid.c | 15 ++++++++++++--- > > 1 file changed, 12 insertions(+), 3 deletions(-) > > Pushed this to drm-misc-fixes since the commit it fixes is fairly old. > > fdc21c35aaa1 drm/edid: In connector_bad_edid() cap num_of_ext by num_blocks read BTW seems kasan caught this for us [1]. I didn't notice we had a bug open about it until now. Just Chris Wilson mentioned it to me in passing quite a while ago, and I totally forgot about it until I saw your other patch poking around the same code. [1] https://gitlab.freedesktop.org/drm/intel/-/issues/4106
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c index 9c9463ec5465..0383d97c306f 100644 --- a/drivers/gpu/drm/drm_edid.c +++ b/drivers/gpu/drm/drm_edid.c @@ -1840,11 +1840,20 @@ static void connector_bad_edid(struct drm_connector *connector, u8 *edid, int num_blocks) { int i; - u8 num_of_ext = edid[0x7e]; + u8 last_block; + + /* + * 0x7e in the EDID is the number of extension blocks. The EDID + * is 1 (base block) + num_ext_blocks big. That means we can think + * of 0x7e in the EDID of the _index_ of the last block in the + * combined chunk of memory. + */ + last_block = edid[0x7e]; /* Calculate real checksum for the last edid extension block data */ - connector->real_edid_checksum = - drm_edid_block_checksum(edid + num_of_ext * EDID_LENGTH); + if (last_block < num_blocks) + connector->real_edid_checksum = + drm_edid_block_checksum(edid + last_block * EDID_LENGTH); if (connector->bad_edid_counter++ && !drm_debug_enabled(DRM_UT_KMS)) return;
In commit e11f5bd8228f ("drm: Add support for DP 1.4 Compliance edid corruption test") the function connector_bad_edid() started assuming that the memory for the EDID passed to it was big enough to hold `edid[0x7e] + 1` blocks of data (1 extra for the base block). It completely ignored the fact that the function was passed `num_blocks` which indicated how much memory had been allocated for the EDID. Let's fix this by adding a bounds check. This is important for handling the case where there's an error in the first block of the EDID. In that case we will call connector_bad_edid() without having re-allocated memory based on `edid[0x7e]`. Fixes: e11f5bd8228f ("drm: Add support for DP 1.4 Compliance edid corruption test") Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> --- This problem report came up in the context of a patch I sent out [1] and this is my attempt at a fix. The problem predates my patch, though. I don't personally know anything about DP compliance testing and what should be happening here, nor do I apparently have any hardware that actually reports a bad EDID. Thus this is just compile tested. I'm hoping that someone here can test this and make sure it seems OK to them. Changes in v2: - Added a comment/changed math to help make it easier to grok. drivers/gpu/drm/drm_edid.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)