[3.10] gh-148395: Fix a possible UAF in `{LZMA,BZ2}Decompressor` (GH-148396) (#148505)

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

(cherry picked from commit 8fc66aef6d7b3ae58f43f5c66f9366cc8cbbfcd2)

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

diff --git a/Misc/NEWS.d/next/Security/2026-04-10-16-28-21.gh-issue-148395.kfzm0G.rst b/Misc/NEWS.d/next/Security/2026-04-10-16-28-21.gh-issue-148395.kfzm0G.rst
new file mode 100644
index 0000000..b095329
--- /dev/null
+++ b/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`,
+: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

diff --git a/Modules/_bz2module.c b/Modules/_bz2module.c
index 798e9ef..b08ac5e 100644
--- a/Modules/_bz2module.c
+++ b/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

diff --git a/Modules/_lzmamodule.c b/Modules/_lzmamodule.c
index 915c0c9..52087c3 100644
--- a/Modules/_lzmamodule.c
+++ b/Modules/_lzmamodule.c
@@ -1102,6 +1102,7 @@ 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;
 }