drm: edid: Add some bounds checking

Make sure drm_detect_hdmi_monitor() and drm_detect_monitor_audio() don't
access beyond the extension block.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index bcc472572cd09741e38683f4a7d9c62cec5f1c3e..7f392534abcc5c50f82c810384e98574d73ada5c 100644 (file)
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -1516,6 +1516,40 @@ do_cea_modes (struct drm_connector *connector, u8 *db, u8 len)
        return modes;
 }
 
+static int
+cea_db_payload_len(const u8 *db)
+{
+       return db[0] & 0x1f;
+}
+
+static int
+cea_db_tag(const u8 *db)
+{
+       return db[0] >> 5;
+}
+
+static int
+cea_revision(const u8 *cea)
+{
+       return cea[1];
+}
+
+static int
+cea_db_offsets(const u8 *cea, int *start, int *end)
+{
+       /* Data block offset in CEA extension block */
+       *start = 4;
+       *end = cea[2];
+       if (*end == 0)
+               *end = 127;
+       if (*end < 4 || *end > 127)
+               return -ERANGE;
+       return 0;
+}
+
+#define for_each_cea_db(cea, i, start, end) \
+       for ((i) = (start); (i) < (end) && (i) + cea_db_payload_len(&(cea)[(i)]) < (end); (i) += cea_db_payload_len(&(cea)[(i)]) + 1)
+
 static int
 add_cea_modes(struct drm_connector *connector, struct edid *edid)
 {
@@ -1523,10 +1557,17 @@ add_cea_modes(struct drm_connector *connector, struct edid *edid)
        u8 * db, dbl;
        int modes = 0;
 
-       if (cea && cea[1] >= 3) {
-               for (db = cea + 4; db < cea + cea[2]; db += dbl + 1) {
-                       dbl = db[0] & 0x1f;
-                       if (((db[0] & 0xe0) >> 5) == VIDEO_BLOCK)
+       if (cea && cea_revision(cea) >= 3) {
+               int i, start, end;
+
+               if (cea_db_offsets(cea, &start, &end))
+                       return 0;
+
+               for_each_cea_db(cea, i, start, end) {
+                       db = &cea[i];
+                       dbl = cea_db_payload_len(db);
+
+                       if (cea_db_tag(db) == VIDEO_BLOCK)
                                modes += do_cea_modes (connector, db+1, dbl);
                }
        }
@@ -1617,19 +1658,29 @@ void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
        eld[18] = edid->prod_code[0];
        eld[19] = edid->prod_code[1];
 
-       if (cea[1] >= 3)
-               for (db = cea + 4; db < cea + cea[2]; db += dbl + 1) {
-                       dbl = db[0] & 0x1f;
-                       
-                       switch ((db[0] & 0xe0) >> 5) {
+       if (cea_revision(cea) >= 3) {
+               int i, start, end;
+
+               if (cea_db_offsets(cea, &start, &end)) {
+                       start = 0;
+                       end = 0;
+               }
+
+               for_each_cea_db(cea, i, start, end) {
+                       db = &cea[i];
+                       dbl = cea_db_payload_len(db);
+
+                       switch (cea_db_tag(db)) {
                        case AUDIO_BLOCK:
                                /* Audio Data Block, contains SADs */
                                sad_count = dbl / 3;
-                               memcpy(eld + 20 + mnl, &db[1], dbl);
+                               if (dbl >= 1)
+                                       memcpy(eld + 20 + mnl, &db[1], dbl);
                                break;
                        case SPEAKER_BLOCK:
-                                /* Speaker Allocation Data Block */
-                               eld[7] = db[1];
+                               /* Speaker Allocation Data Block */
+                               if (dbl >= 1)
+                                       eld[7] = db[1];
                                break;
                        case VENDOR_BLOCK:
                                /* HDMI Vendor-Specific Data Block */
@@ -1640,6 +1691,7 @@ void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
                                break;
                        }
                }
+       }
        eld[5] |= sad_count << 4;
        eld[2] = (20 + mnl + sad_count * 3 + 3) / 4;
 
@@ -1725,19 +1777,16 @@ bool drm_detect_hdmi_monitor(struct edid *edid)
        if (!edid_ext)
                goto end;
 
-       /* Data block offset in CEA extension block */
-       start_offset = 4;
-       end_offset = edid_ext[2];
+       if (cea_db_offsets(edid_ext, &start_offset, &end_offset))
+               goto end;
 
        /*
         * Because HDMI identifier is in Vendor Specific Block,
         * search it from all data blocks of CEA extension.
         */
-       for (i = start_offset; i < end_offset;
-               /* Increased by data block len */
-               i += ((edid_ext[i] & 0x1f) + 1)) {
+       for_each_cea_db(edid_ext, i, start_offset, end_offset) {
                /* Find vendor specific block */
-               if ((edid_ext[i] >> 5) == VENDOR_BLOCK) {
+               if (cea_db_tag(&edid_ext[i]) == VENDOR_BLOCK) {
                        hdmi_id = edid_ext[i + 1] | (edid_ext[i + 2] << 8) |
                                  edid_ext[i + 3] << 16;
                        /* Find HDMI identifier */
@@ -1780,15 +1829,13 @@ bool drm_detect_monitor_audio(struct edid *edid)
                goto end;
        }
 
-       /* Data block offset in CEA extension block */
-       start_offset = 4;
-       end_offset = edid_ext[2];
+       if (cea_db_offsets(edid_ext, &start_offset, &end_offset))
+               goto end;
 
-       for (i = start_offset; i < end_offset;
-                       i += ((edid_ext[i] & 0x1f) + 1)) {
-               if ((edid_ext[i] >> 5) == AUDIO_BLOCK) {
+       for_each_cea_db(edid_ext, i, start_offset, end_offset) {
+               if (cea_db_tag(&edid_ext[i]) == AUDIO_BLOCK) {
                        has_audio = true;
-                       for (j = 1; j < (edid_ext[i] & 0x1f); j += 3)
+                       for (j = 1; j < cea_db_payload_len(&edid_ext[i]) + 1; j += 3)
                                DRM_DEBUG_KMS("CEA audio format %d\n",
                                              (edid_ext[i + j] >> 3) & 0xf);
                        goto end;