Handle multiple and malformed JPEG APP13 markers

Tests/test_file_jpeg.py

@@ -676,6 +676,13 @@ def test_photoshop(self):
         with Image.open("Tests/images/app13.jpg") as im:
             self.assertNotIn("photoshop", im.info)
 
+    def test_photoshop_malformed_and_multiple(self):
+        with Image.open("Tests/images/app13-multiple.jpg") as im:
+            self.assertIn("photoshop", im.info)
+            self.assertEqual(24, len(im.info["photoshop"]))
+            apps_13_lengths = [len(v) for k, v in im.applist if k == "APP13"]
+            self.assertEqual([65504, 24], apps_13_lengths)
+
 
 @unittest.skipUnless(is_win32(), "Windows only")
 class TestFileCloseW32(PillowTestCase):

src/PIL/JpegImagePlugin.py

@@ -100,30 +100,25 @@ def APP(self, marker):
         # reassemble the profile, rather than assuming that the APP2
         # markers appear in the correct sequence.
         self.icclist.append(s)
-    elif marker == 0xFFED:
-        if s[:14] == b"Photoshop 3.0\x00":
-            blocks = s[14:]
-            # parse the image resource block
-            offset = 0
-            photoshop = {}
-            while blocks[offset : offset + 4] == b"8BIM":
+    elif marker == 0xFFED and s[:14] == b"Photoshop 3.0\x00":
+        # parse the image resource block
+        offset = 14
+        photoshop = self.info.setdefault("photoshop", {})
+        while s[offset : offset + 4] == b"8BIM":
+            try:
                 offset += 4
                 # resource code
-                try:
-                    code = i16(blocks, offset)
-                except struct.error:
-                    break
+                code = i16(s, offset)
                 offset += 2
                 # resource name (usually empty)
-                name_len = i8(blocks[offset])
-                # name = blocks[offset+1:offset+1+name_len]
-                offset = 1 + offset + name_len
-                if offset & 1:
-                    offset += 1
+                name_len = i8(s[offset])
+                # name = s[offset+1:offset+1+name_len]
+                offset += 1 + name_len
+                offset += offset & 1  # align
                 # resource data block
-                size = i32(blocks, offset)
+                size = i32(s, offset)
                 offset += 4
-                data = blocks[offset : offset + size]
+                data = s[offset : offset + size]
                 if code == 0x03ED:  # ResolutionInfo
                     data = {
                         "XResolution": i32(data[:4]) / 65536,
@@ -132,10 +127,11 @@ def APP(self, marker):
                         "DisplayedUnitsY": i16(data[12:]),
                     }
                 photoshop[code] = data
-                offset = offset + size
-                if offset & 1:
-                    offset += 1
-            self.info["photoshop"] = photoshop
+                offset += size
+                offset += offset & 1  # align
+            except struct.error:
+                break  # insufficient data
+
     elif marker == 0xFFEE and s[:5] == b"Adobe":
         self.info["adobe"] = i16(s, 5)
         # extract Adobe custom properties