linux-kernel - [PATCH] [next] drm/radeon: Replace one-element array with flexible-array member

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Date:   Fri, 28 Oct 2022 18:41:25 +1300
From:   Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@...il.com>
To:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        paulo.miguel.almeida.rodenas@...il.com
Subject: [PATCH] [next] drm/radeon: Replace one-element array with
 flexible-array member

One-element arrays are deprecated, and we are replacing them with
flexible array members instead. So, replace one-element array with
flexible-array member in struct _ATOM_FAKE_EDID_PATCH_RECORD and
refactor the rest of the code accordingly.

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
routines on memcpy() and help us make progress towards globally
enabling -fstrict-flex-arrays=3 [1].

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/239
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836 [1]

Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@...il.com>
---
 drivers/gpu/drm/radeon/atombios.h        |  2 +-
 drivers/gpu/drm/radeon/radeon_atombios.c | 12 ++++++++----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/radeon/atombios.h b/drivers/gpu/drm/radeon/atombios.h
index da35a970fcc0..235e59b547a1 100644
--- a/drivers/gpu/drm/radeon/atombios.h
+++ b/drivers/gpu/drm/radeon/atombios.h
@@ -3615,7 +3615,7 @@ typedef struct _ATOM_FAKE_EDID_PATCH_RECORD
 {
   UCHAR ucRecordType;
   UCHAR ucFakeEDIDLength;
-  UCHAR ucFakeEDIDString[1];    // This actually has ucFakeEdidLength elements.
+  UCHAR ucFakeEDIDString[];    // This actually has ucFakeEdidLength elements.
 } ATOM_FAKE_EDID_PATCH_RECORD;
 
 typedef struct  _ATOM_PANEL_RESOLUTION_PATCH_RECORD
diff --git a/drivers/gpu/drm/radeon/radeon_atombios.c b/drivers/gpu/drm/radeon/radeon_atombios.c
index 204127bad89c..48de2521f253 100644
--- a/drivers/gpu/drm/radeon/radeon_atombios.c
+++ b/drivers/gpu/drm/radeon/radeon_atombios.c
@@ -1716,7 +1716,7 @@ struct radeon_encoder_atom_dig *radeon_atombios_get_lvds_info(struct
 							max((int)EDID_LENGTH, (int)fake_edid_record->ucFakeEDIDLength);
 						edid = kmalloc(edid_size, GFP_KERNEL);
 						if (edid) {
-							memcpy((u8 *)edid, (u8 *)&fake_edid_record->ucFakeEDIDString[0],
+							memcpy((u8 *)edid, (u8 *)fake_edid_record->ucFakeEDIDString,
 							       fake_edid_record->ucFakeEDIDLength);
 
 							if (drm_edid_is_valid(edid)) {
@@ -1725,10 +1725,14 @@ struct radeon_encoder_atom_dig *radeon_atombios_get_lvds_info(struct
 							} else
 								kfree(edid);
 						}
+
+						record += struct_size(fake_edid_record,
+								      ucFakeEDIDString,
+								      fake_edid_record->ucFakeEDIDLength);
+					} else {
+						/* empty fake edid record must be 3 bytes long */
+						record += sizeof(*fake_edid_record) + 1;
 					}
-					record += fake_edid_record->ucFakeEDIDLength ?
-						fake_edid_record->ucFakeEDIDLength + 2 :
-						sizeof(ATOM_FAKE_EDID_PATCH_RECORD);
 					break;
 				case LCD_PANEL_RESOLUTION_RECORD_TYPE:
 					panel_res_record = (ATOM_PANEL_RESOLUTION_PATCH_RECORD *)record;
-- 
2.37.3