Fix OOB Read in Jpeg2KDecode CVE-2021-25287,CVE-2021-25288

* For J2k images with multiple bands, it's legal in to have different
  widths for each band, e.g. 1 byte for L, 4 bytes for A
* This dates to Pillow 2.4.0

Tests/test_file_jpeg2k.py

@@ -231,3 +231,19 @@ def test_parser_feed():
 
     # Assert
     assert p.image.size == (640, 480)
+
+
+@pytest.mark.parametrize(
+    "test_file",
+    [
+        "Tests/images/crash-4fb027452e6988530aa5dabee76eecacb3b79f8a.j2k",
+        "Tests/images/crash-7d4c83eb92150fb8f1653a697703ae06ae7c4998.j2k",
+        "Tests/images/crash-ccca68ff40171fdae983d924e127a721cab2bd50.j2k",
+        "Tests/images/crash-d2c93af851d3ab9a19e34503626368b2ecde9c03.j2k",
+    ],
+)
+def test_crashes(test_file):
+    with open(test_file, "rb") as f:
+        with Image.open(f) as im:
+            # Valgrind should not complain here
+            im.load()

src/libImaging/Jpeg2KDecode.c

@@ -644,7 +644,7 @@ j2k_decode_entry(Imaging im, ImagingCodecState state) {
     j2k_unpacker_t unpack = NULL;
     size_t buffer_size = 0, tile_bytes = 0;
     unsigned n, tile_height, tile_width;
-    int components;
+    int total_component_width = 0;
 
     stream = opj_stream_create(BUFFER_SIZE, OPJ_TRUE);
 
@@ -814,23 +814,40 @@ j2k_decode_entry(Imaging im, ImagingCodecState state) {
             goto quick_exit;
         }
 
+        if (tile_info.nb_comps != image->numcomps) {
+            state->errcode = IMAGING_CODEC_BROKEN;
+            state->state = J2K_STATE_FAILED;
+            goto quick_exit;
+        }
+
         /* Sometimes the tile_info.datasize we get back from openjpeg
-           is less than numcomps*w*h, and we overflow in the
+           is less than sum(comp_bytes)*w*h, and we overflow in the
            shuffle stage */
 
         tile_width = tile_info.x1 - tile_info.x0;
         tile_height = tile_info.y1 - tile_info.y0;
-        components = tile_info.nb_comps == 3 ? 4 : tile_info.nb_comps;
-        if ((tile_width > UINT_MAX / components) ||
-            (tile_height > UINT_MAX / components) ||
-            (tile_width > UINT_MAX / (tile_height * components)) ||
-            (tile_height > UINT_MAX / (tile_width * components))) {
+
+        /* Total component width = sum (component_width) e.g, it's
+         legal for an la file to have a 1 byte width for l, and 4 for
+         a. and then a malicious file could have a smaller tile_bytes
+        */
+
+        for (n=0; n < tile_info.nb_comps; n++) {
+            // see csize /acsize calcs
+            int csize = (image->comps[n].prec + 7) >> 3;
+            csize = (csize == 3) ? 4 : csize;
+            total_component_width += csize;
+        }
+        if ((tile_width > UINT_MAX / total_component_width) ||
+            (tile_height > UINT_MAX / total_component_width) ||
+            (tile_width > UINT_MAX / (tile_height * total_component_width)) ||
+            (tile_height > UINT_MAX / (tile_width * total_component_width))) {
             state->errcode = IMAGING_CODEC_BROKEN;
             state->state = J2K_STATE_FAILED;
             goto quick_exit;
         }
 
-        tile_bytes = tile_width * tile_height * components;
+        tile_bytes = tile_width * tile_height * total_component_width;
 
         if (tile_bytes > tile_info.data_size) {
             tile_info.data_size = tile_bytes;