| Message ID | 20211005081022.1.Ib059f9c23c2611cb5a9d760e7d0a700c1295928d@changeid (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/edid: In connector_bad_edid() cap num_of_ext by num_blocks read | expand |
On Tue, Oct 05, 2021 at 08:10:28AM -0700, Douglas Anderson 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> > --- > 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. > > drivers/gpu/drm/drm_edid.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c > index 9b19eee0e1b4..ccfa08631c57 100644 > --- a/drivers/gpu/drm/drm_edid.c > +++ b/drivers/gpu/drm/drm_edid.c > @@ -1843,8 +1843,9 @@ static void connector_bad_edid(struct drm_connector *connector, > u8 num_of_ext = 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 (num_of_ext <= num_blocks - 1) Something about that doesn't really agree with my brain. It's correct but when I read it I can't immediately see it. I guess what I'd like to see is something like: last_block = edid[0x7e]; if (last_block < num_blocks) connector->real_edid_checksum = drm_edid_block_checksum(edid + last_block * EDID_LENGTH); Techically exactly the same thing, but I don't have to read the comparison twice to convince myself that it's correct. Anyways, this is Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> either way. > + connector->real_edid_checksum = > + drm_edid_block_checksum(edid + num_of_ext * EDID_LENGTH); > > if (connector->bad_edid_counter++ && !drm_debug_enabled(DRM_UT_KMS)) > return; > -- > 2.33.0.800.g4c38ced690-goog
Hi, On Tue, Oct 5, 2021 at 8:46 AM Ville Syrjälä <ville.syrjala@linux.intel.com> wrote: > > On Tue, Oct 05, 2021 at 08:10:28AM -0700, Douglas Anderson 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> > > --- > > 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. > > > > drivers/gpu/drm/drm_edid.c | 5 +++-- > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c > > index 9b19eee0e1b4..ccfa08631c57 100644 > > --- a/drivers/gpu/drm/drm_edid.c > > +++ b/drivers/gpu/drm/drm_edid.c > > @@ -1843,8 +1843,9 @@ static void connector_bad_edid(struct drm_connector *connector, > > u8 num_of_ext = 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 (num_of_ext <= num_blocks - 1) > > Something about that doesn't really agree with my brain. > It's correct but when I read it I can't immediately see it. > > I guess what I'd like to see is something like: > last_block = edid[0x7e]; > if (last_block < num_blocks) > connector->real_edid_checksum = > drm_edid_block_checksum(edid + last_block * EDID_LENGTH); > > Techically exactly the same thing, but I don't have to read > the comparison twice to convince myself that it's correct. > > Anyways, this is > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> > either way. Yeah, my brain had to work way too hard when I read over my patch too. I've changed to your math _plus_ a big comment explaining it. I added your review tag. I'll give this another day or so and then land. https://lore.kernel.org/r/20211005192905.v2.1.Ib059f9c23c2611cb5a9d760e7d0a700c1295928d@changeid -Doug
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c index 9b19eee0e1b4..ccfa08631c57 100644 --- a/drivers/gpu/drm/drm_edid.c +++ b/drivers/gpu/drm/drm_edid.c @@ -1843,8 +1843,9 @@ static void connector_bad_edid(struct drm_connector *connector, u8 num_of_ext = 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 (num_of_ext <= num_blocks - 1) + connector->real_edid_checksum = + drm_edid_block_checksum(edid + num_of_ext * 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> --- 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. drivers/gpu/drm/drm_edid.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)