[3.11] gh-148395: Fix a possible UAF in {LZMA,BZ2}Decompressor (GH-148396) (#148504)

Fix dangling input pointer after `MemoryError` in _lzma/_bz2/_ZlibDecompressor.decompress

(cherry picked from commit 8fc66ae)

Author: StanFromIreland

Misc/NEWS.d/next/Security/2026-04-10-16-28-21.gh-issue-148395.kfzm0G.rst

@@ -0,0 +1,5 @@
+Fix a dangling input pointer in :class:`lzma.LZMADecompressor`,
+and :class:`bz2.BZ2Decompressor`
+when memory allocation fails with :exc:`MemoryError`, which could let a
+subsequent :meth:`!decompress` call read or write through a stale pointer to
+the already-released caller buffer.

Modules/_bz2module.c

@@ -595,6 +595,7 @@ decompress(BZ2Decompressor *d, char *data, size_t len, Py_ssize_t max_length)
     return result;
 
 error:
+    bzs->next_in = NULL;
     Py_XDECREF(result);
     return NULL;
 }

Modules/_lzmamodule.c

@@ -1105,6 +1105,7 @@ decompress(Decompressor *d, uint8_t *data, size_t len, Py_ssize_t max_length)
     return result;
 
 error:
+    lzs->next_in = NULL;
     Py_XDECREF(result);
     return NULL;
 }