Close #16742: Fix misuse of memory allocations in PyOS_Readline()

The GIL must be held to call PyMem_Malloc(), whereas PyOS_Readline() releases
the GIL to read input.

The result of the C callback PyOS_ReadlineFunctionPointer must now be a string
allocated by PyMem_RawMalloc() or PyMem_RawRealloc() (or NULL if an error
occurred), instead of a string allocated by PyMem_Malloc() or PyMem_Realloc().

Fixing this issue was required to setup a hook on PyMem_Malloc(), for example
using the tracemalloc module.

PyOS_Readline() copies the result of PyOS_ReadlineFunctionPointer() into a new
buffer allocated by PyMem_Malloc(). So the public API of PyOS_Readline() does
not change.

1 files changed, 2 insertions, 2 deletions

diff --git a/Modules/readline.c b/Modules/readline.c
index c154e1d..668ee02 100644
--- a/Modules/readline.c
+++ b/Modules/readline.c
@@ -1176,7 +1176,7 @@ call_readline(FILE *sys_stdin, FILE *sys_stdout, char *prompt)
 
     /* We got an EOF, return a empty string. */
     if (p == NULL) {
-        p = PyMem_Malloc(1);
+        p = PyMem_RawMalloc(1);
         if (p != NULL)
             *p = '\0';
         RESTORE_LOCALE(saved_locale)
@@ -1204,7 +1204,7 @@ call_readline(FILE *sys_stdin, FILE *sys_stdout, char *prompt)
     /* Copy the malloc'ed buffer into a PyMem_Malloc'ed one and
        release the original. */
     q = p;
-    p = PyMem_Malloc(n+2);
+    p = PyMem_RawMalloc(n+2);
     if (p != NULL) {
         strncpy(p, q, n);
         p[n] = '\n';