Commit message: gallium/tgsi: fix oob access in parse instruction

When parsing texture instruction, it doesn't stop if the
'cur' is ',', the loop variable 'i' will also be increased
and be used to index the 'inst.TexOffsets' array. This can lead
an oob access issue. This patch avoid this.

Signed-off-by: Li Qiang <liq3ea@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
CVE: CVE-2017-5580
CWE: CWE-119
Vulnerability description: The parse_instruction function in gallium/auxiliary/tgsi/tgsi_text.c in virglrenderer before 0.6.0 allows local guest OS users to cause a denial of service (out-of-bounds array access and process crash) via a crafted texture instruction.

Project: virglrenderer
File: tgsi_text.c

parse_instruction(
   struct translate_ctx *ctx,
   boolean has_label )
{
   uint i;
   uint saturate = 0;
   const struct tgsi_opcode_info *info;
   struct tgsi_full_instruction inst;
   const char *cur;
   uint advance;

   inst = tgsi_default_full_instruction();

   /* Parse predicate.
    */
   eat_opt_white( &ctx->cur );
   if (*ctx->cur == '(') {
      uint file;
      int index;
      uint swizzle[4];
      boolean parsed_swizzle;

      inst.Instruction.Predicate = 1;

      ctx->cur++;
      if (*ctx->cur == '!') {
         ctx->cur++;
         inst.Predicate.Negate = 1;
      }

      if (!parse_register_1d( ctx, &file, &index ))
         return FALSE;

      if (parse_optional_swizzle( ctx, swizzle, &parsed_swizzle, 4 )) {
         if (parsed_swizzle) {
            inst.Predicate.SwizzleX = swizzle[0];
            inst.Predicate.SwizzleY = swizzle[1];
            inst.Predicate.SwizzleZ = swizzle[2];
            inst.Predicate.SwizzleW = swizzle[3];
         }
      }

      if (*ctx->cur != ')') {
         report_error( ctx, "Expected `)'" );
         return FALSE;
      }

      ctx->cur++;
   }

   /* Parse instruction name.
    */
   eat_opt_white( &ctx->cur );
   for (i = 0; i < TGSI_OPCODE_LAST; i++) {
      cur = ctx->cur;

      info = tgsi_get_opcode_info( i );
      if (match_inst(&cur, &saturate, info)) {
         if (info->num_dst + info->num_src + info->is_tex == 0) {
            ctx->cur = cur;
            break;
         }
         else if (*cur == '\0' || eat_white( &cur )) {
            ctx->cur = cur;
            break;
         }
      }
   }
   if (i == TGSI_OPCODE_LAST) {
      if (has_label)
         report_error( ctx, "Unknown opcode" );
      else
         report_error( ctx, "Expected `DCL', `IMM' or a label" );
      return FALSE;
   }

   inst.Instruction.Opcode = i;
   inst.Instruction.Saturate = saturate;
   inst.Instruction.NumDstRegs = info->num_dst;
   inst.Instruction.NumSrcRegs = info->num_src;

   if (i >= TGSI_OPCODE_SAMPLE && i <= TGSI_OPCODE_GATHER4) {
      /*
       * These are not considered tex opcodes here (no additional
       * target argument) however we're required to set the Texture
       * bit so we can set the number of tex offsets.
       */
      inst.Instruction.Texture = 1;
      inst.Texture.Texture = TGSI_TEXTURE_UNKNOWN;
   }

   /* Parse instruction operands.
    */
   for (i = 0; i < info->num_dst + info->num_src + info->is_tex; i++) {
      if (i > 0) {
         eat_opt_white( &ctx->cur );
         if (*ctx->cur != ',') {
            report_error( ctx, "Expected `,'" );
            return FALSE;
         }
         ctx->cur++;
         eat_opt_white( &ctx->cur );
      }

      if (i < info->num_dst) {
         if (!parse_dst_operand( ctx, &inst.Dst[i] ))
            return FALSE;
      }
      else if (i < info->num_dst + info->num_src) {
         if (!parse_src_operand( ctx, &inst.Src[i - info->num_dst] ))
            return FALSE;
      }
      else {
         uint j;

         for (j = 0; j < TGSI_TEXTURE_COUNT; j++) {
            if (str_match_nocase_whole( &ctx->cur, tgsi_texture_names[j] )) {
               inst.Instruction.Texture = 1;
               inst.Texture.Texture = j;
               break;
            }
         }
         if (j == TGSI_TEXTURE_COUNT) {
            report_error( ctx, "Expected texture target" );
            return FALSE;
         }
      }
   }
 
    cur = ctx->cur;
    eat_opt_white( &cur );
   for (i = 0; inst.Instruction.Texture && *cur == ','; i++) {
          cur++;
          eat_opt_white( &cur );
          ctx->cur = cur;
         if (!parse_texoffset_operand( ctx, &inst.TexOffsets[i] ))
            return FALSE;
         cur = ctx->cur;
         eat_opt_white( &cur );
   }
   inst.Texture.NumOffsets = i;

   cur = ctx->cur;
   eat_opt_white( &cur );
   if (info->is_branch && *cur == ':') {
      uint target;

      cur++;
      eat_opt_white( &cur );
      if (!parse_uint( &cur, &target )) {
         report_error( ctx, "Expected a label" );
         return FALSE;
      }
      inst.Instruction.Label = 1;
      inst.Label.Label = target;
      ctx->cur = cur;
   }

   advance = tgsi_build_full_instruction(
      &inst,
      ctx->tokens_cur,
      ctx->header,
      (uint) (ctx->tokens_end - ctx->tokens_cur) );
   if (advance == 0)
      return FALSE;
   ctx->tokens_cur += advance;

   return TRUE;
}