From 76d0c4b6885365a08e840d99ab948ab2b7c4a34e Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Wed, 17 Jan 2024 14:30:29 +0100
Subject: [3.11] gh-104282: Fix null pointer dereference in
 `lzma._decode_filter_properties` (GH-104283) (GH-114182)

(cherry picked from commit 0154405350c272833bd51f68138223655e142a37)

Co-authored-by: Radislav Chugunov <52372310+chgnrdv@users.noreply.github.com>
---
 Lib/test/test_lzma.py                                             | 8 ++++++++
 .../next/Library/2023-05-08-09-30-00.gh-issue-104282.h4c6Eb.rst   | 3 +++
 Modules/_lzmamodule.c                                             | 4 +++-
 3 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2023-05-08-09-30-00.gh-issue-104282.h4c6Eb.rst

diff --git a/Lib/test/test_lzma.py b/Lib/test/test_lzma.py
index 49042d7..d2ae133 100644
--- a/Lib/test/test_lzma.py
+++ b/Lib/test/test_lzma.py
@@ -1409,6 +1409,14 @@ class MiscellaneousTestCase(unittest.TestCase):
         self.assertEqual(filterspec["lc"], 3)
         self.assertEqual(filterspec["dict_size"], 8 << 20)
 
+        # see gh-104282
+        filters = [lzma.FILTER_X86, lzma.FILTER_POWERPC,
+                   lzma.FILTER_IA64, lzma.FILTER_ARM,
+                   lzma.FILTER_ARMTHUMB, lzma.FILTER_SPARC]
+        for f in filters:
+            filterspec = lzma._decode_filter_properties(f, b"")
+            self.assertEqual(filterspec, {"id": f})
+
     def test_filter_properties_roundtrip(self):
         spec1 = lzma._decode_filter_properties(
                 lzma.FILTER_LZMA1, b"]\x00\x00\x80\x00")
diff --git a/Misc/NEWS.d/next/Library/2023-05-08-09-30-00.gh-issue-104282.h4c6Eb.rst b/Misc/NEWS.d/next/Library/2023-05-08-09-30-00.gh-issue-104282.h4c6Eb.rst
new file mode 100644
index 0000000..569ce66
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-05-08-09-30-00.gh-issue-104282.h4c6Eb.rst
@@ -0,0 +1,3 @@
+Fix null pointer dereference in :func:`lzma._decode_filter_properties`
+due to improper handling of BCJ filters with properties of zero length.
+Patch by Radislav Chugunov.
diff --git a/Modules/_lzmamodule.c b/Modules/_lzmamodule.c
index b572d8c..97453a2 100644
--- a/Modules/_lzmamodule.c
+++ b/Modules/_lzmamodule.c
@@ -494,7 +494,9 @@ build_filter_spec(const lzma_filter *f)
         case LZMA_FILTER_ARMTHUMB:
         case LZMA_FILTER_SPARC: {
             lzma_options_bcj *options = f->options;
-            ADD_FIELD(options, start_offset);
+            if (options) {
+                ADD_FIELD(options, start_offset);
+            }
             break;
         }
         default:
-- 
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