drm/amd/display: Fix out-of-bounds stream encoder index v3

CVE-2026-46263

What is CVE-2026-46263?

In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: Fix out-of-bounds stream encoder index v3

eng_id can be negative and that stream_enc_regs[] can be indexed out of bounds.

eng_id is used directly as an index into stream_enc_regs[], which has only 5 entries. When eng_id is 5 (ENGINE_ID_DIGF) or negative, this can access memory past the end of the array.

Add a bounds check using ARRAY_SIZE() before using eng_id as an index. The unsigned cast also rejects negative values.

This avoids out-of-bounds access.

Fixes the below smatch error: dcn*_resource.c: stream_encoder_create() may index stream_enc_regs[eng_id] out of bounds (size 5).

drivers/gpu/drm/amd/amdgpu/../display/dc/resource/dcn351/dcn351_resource.c 1246 static struct stream_encoder *dcn35_stream_encoder_create( 1247 enum engine_id eng_id, 1248 struct dc_context *ctx) 1249 {

...

1255
1256         /* Mapping of VPG, AFMT, DME register blocks to DIO block instance */
1257         if (eng_id <= ENGINE_ID_DIGF) {

ENGINE_ID_DIGF is 5. should <= be <?

Unrelated but, ugh, why is Smatch saying that "eng_id" can be negative? end_id is type signed long, but there are checks in the caller which prevent it from being negative.

1258                 vpg_inst = eng_id;
1259                 afmt_inst = eng_id;
1260         } else
1261                 return NULL;
1262

...

1281
1282         dcn35_dio_stream_encoder_construct(enc1, ctx, ctx->dc_bios,
1283                                         eng_id, vpg, afmt,

--> 1284 &stream_enc_regs[eng_id], ^^^^^^^^^^^^^^^^^^^^^^^ This stream_enc_regs[] array has 5 elements so we are one element beyond the end of the array.

...

1287         return &enc1->base;
1288 }

v2: use explicit bounds check as suggested by Roman/Dan; avoid unsigned int cast

v3: The compiler already knows how to compare the two values, so the cast (int) is not needed. (Roman)

References