From cbdc7516280776945579d14c017a0d636a9df9e4 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Tue, 10 Aug 2021 07:04:36 +1000
Subject: [PATCH] Read AND mask from end

---
 Tests/images/hopper_mask.ico | Bin 0 -> 262 bytes
 Tests/images/hopper_mask.png | Bin 0 -> 208 bytes
 Tests/test_file_ico.py       |   5 +++++
 src/PIL/IcoImagePlugin.py    |   2 +-
 4 files changed, 6 insertions(+), 1 deletion(-)
 create mode 100644 Tests/images/hopper_mask.ico
 create mode 100644 Tests/images/hopper_mask.png

diff --git a/Tests/images/hopper_mask.ico b/Tests/images/hopper_mask.ico
new file mode 100644
index 0000000000000000000000000000000000000000..e8d66c689fd42918c887a316f34a8e0d3ae8c154
GIT binary patch
literal 262
zcmZQzU<5(|0R|voWcUCi#ei4?h(SUMKn#)x0S6#H!Uw@jKsE@2z<(eB(WVVRwX8sK
zP6h^MAls>vfx&}^fkEU61B2iT1_s_L28MSJ7#LdT0~I#{)dDSQ{l~z-X#g|>C^V25
E0C?>&ZU6uP

literal 0
HcmV?d00001

diff --git a/Tests/images/hopper_mask.png b/Tests/images/hopper_mask.png
new file mode 100644
index 0000000000000000000000000000000000000000..c7bd2f70842801aa0db7150ece834f839cf10376
GIT binary patch
literal 208
zcmeAS@N?(olHy`uVBq!ia0vp^0wB!61|;P_|4#%`(>+}rLn`L<21oN9Q4nZa_I<z6
z-<54jyRws-k}G|Tg*K`*E=lI)Nx0YRs=nlechD>!qfYIUFP)0s%}Q9FmwCm<?b7dl
zF}ts-YsDvjnfLU$>w=?2hLgO~cOSmGXm_xh*B`+Q&1olYF0)pbt5W}{+Q^;C{dV?S
z8Hqw`c2h^It&)X%L^GPNyb5**di(nezsJ8iZi_u`3>6H8wpEfdPQP6NbRvVNtDnm{
Hr-UW|-Oo~i

literal 0
HcmV?d00001

diff --git a/Tests/test_file_ico.py b/Tests/test_file_ico.py
index 8060d1b763b..317264db646 100644
--- a/Tests/test_file_ico.py
+++ b/Tests/test_file_ico.py
@@ -18,6 +18,11 @@ def test_sanity():
     assert im.get_format_mimetype() == "image/x-icon"
 
 
+def test_mask():
+    with Image.open("Tests/images/hopper_mask.ico") as im:
+        assert_image_equal_tofile(im, "Tests/images/hopper_mask.png")
+
+
 def test_black_and_white():
     with Image.open("Tests/images/black_and_white.ico") as im:
         assert im.mode == "RGBA"
diff --git a/src/PIL/IcoImagePlugin.py b/src/PIL/IcoImagePlugin.py
index ffb1e873d23..d9ff9b5e731 100644
--- a/src/PIL/IcoImagePlugin.py
+++ b/src/PIL/IcoImagePlugin.py
@@ -235,8 +235,8 @@ def frame(self, idx):
                 # the total mask data is
                 # padded row size * height / bits per char
 
-                and_mask_offset = o + int(im.size[0] * im.size[1] * (bpp / 8.0))
                 total_bytes = int((w * im.size[1]) / 8)
+                and_mask_offset = header["offset"] + header["size"] - total_bytes
 
                 self.buf.seek(and_mask_offset)
                 mask_data = self.buf.read(total_bytes)