[Python-checkins] gh-88116: Avoid undefined behavior when decoding varints in code objects (#94375)

[pablogsal]

https://github.com/python/cpython/commit/c485ec014ce174bb3f5ae948151dc40e0f6d5f7f
commit: c485ec014ce174bb3f5ae948151dc40e0f6d5f7f
branch: main
author: Pablo Galindo Salgado <Pablogsal at gmail.com>
committer: pablogsal <Pablogsal at gmail.com>
date: 2022-06-28T14:24:54+01:00
summary:

gh-88116: Avoid undefined behavior when decoding varints in code objects (#94375)

files:
A Misc/NEWS.d/next/Core and Builtins/2022-06-28-12-41-17.gh-issue-88116.A7fEl_.rst
M Objects/codeobject.c

diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-06-28-12-41-17.gh-issue-88116.A7fEl_.rst b/Misc/NEWS.d/next/Core and Builtins/2022-06-28-12-41-17.gh-issue-88116.A7fEl_.rst
new file mode 100644
index 0000000000000..a8347cff09f39
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2022-06-28-12-41-17.gh-issue-88116.A7fEl_.rst	
@@ -0,0 +1,2 @@
+Fix an issue when reading line numbers from code objects if the encoded line
+numbers are close to ``INT_MIN``. Patch by Pablo Galindo
diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index c38c51b45321c..6f2a837240384 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -354,9 +354,9 @@ init_code(PyCodeObject *co, struct _PyCodeConstructor *con)
 static int
 scan_varint(const uint8_t *ptr)
 {
-    int read = *ptr++;
-    int val = read & 63;
-    int shift = 0;
+    unsigned int read = *ptr++;
+    unsigned int val = read & 63;
+    unsigned int shift = 0;
     while (read & 64) {
         read = *ptr++;
         shift += 6;
@@ -368,7 +368,7 @@ scan_varint(const uint8_t *ptr)
 static int
 scan_signed_varint(const uint8_t *ptr)
 {
-    int uval = scan_varint(ptr);
+    unsigned int uval = scan_varint(ptr);
     if (uval & 1) {
         return -(int)(uval >> 1);
     }
@@ -847,9 +847,9 @@ read_byte(PyCodeAddressRange *bounds)
 static int
 read_varint(PyCodeAddressRange *bounds)
 {
-    int read = read_byte(bounds);
-    int val = read & 63;
-    int shift = 0;
+    unsigned int read = read_byte(bounds);
+    unsigned int val = read & 63;
+    unsigned int shift = 0;
     while (read & 64) {
         read = read_byte(bounds);
         shift += 6;
@@ -861,7 +861,7 @@ read_varint(PyCodeAddressRange *bounds)
 static int
 read_signed_varint(PyCodeAddressRange *bounds)
 {
-    int uval = read_varint(bounds);
+    unsigned int uval = read_varint(bounds);
     if (uval & 1) {
         return -(int)(uval >> 1);
     }