[3.11] gh-104522: Fix OSError raised when run a subprocess (GH-114195) (GH-114243)

Only set filename to cwd if it was caused by failed chdir(cwd).

_fork_exec() now returns "noexec:chdir" for failed chdir(cwd).

(cherry picked from commit e2c097ebdee447ded1109f99a235e65aa3533bf8)

Co-authored-by: Robert O'Shea <PurityLake@users.noreply.github.com>

1 files changed, 11 insertions, 10 deletions

diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
index 072519c..d91bf21 100644
--- a/Modules/_posixsubprocess.c
+++ b/Modules/_posixsubprocess.c
@@ -566,9 +566,10 @@ child_exec(char *const exec_array[],
            PyObject *preexec_fn,
            PyObject *preexec_fn_args_tuple)
 {
-    int i, saved_errno, reached_preexec = 0;
+    int i, saved_errno;
     PyObject *result;
-    const char* err_msg = "";
+    /* Indicate to the parent that the error happened before exec(). */
+    const char *err_msg = "noexec";
     /* Buffer large enough to hold a hex integer.  We can't malloc. */
     char hex_errno[sizeof(saved_errno)*2+1];
 
@@ -628,8 +629,12 @@ child_exec(char *const exec_array[],
     /* We no longer manually close p2cread, c2pwrite, and errwrite here as
      * _close_open_fds takes care when it is not already non-inheritable. */
 
-    if (cwd)
-        POSIX_CALL(chdir(cwd));
+    if (cwd) {
+        if (chdir(cwd) == -1) {
+            err_msg = "noexec:chdir";
+            goto error;
+        }
+    }
 
     if (child_umask >= 0)
         umask(child_umask);  /* umask() always succeeds. */
@@ -672,7 +677,7 @@ child_exec(char *const exec_array[],
 #endif /* HAVE_SETREUID */
 
 
-    reached_preexec = 1;
+    err_msg = "";
     if (preexec_fn != Py_None && preexec_fn_args_tuple) {
         /* This is where the user has asked us to deadlock their program. */
         result = PyObject_Call(preexec_fn, preexec_fn_args_tuple, NULL);
@@ -730,16 +735,12 @@ error:
         }
         _Py_write_noraise(errpipe_write, cur, hex_errno + sizeof(hex_errno) - cur);
         _Py_write_noraise(errpipe_write, ":", 1);
-        if (!reached_preexec) {
-            /* Indicate to the parent that the error happened before exec(). */
-            _Py_write_noraise(errpipe_write, "noexec", 6);
-        }
         /* We can't call strerror(saved_errno).  It is not async signal safe.
          * The parent process will look the error message up. */
     } else {
         _Py_write_noraise(errpipe_write, "SubprocessError:0:", 18);
-        _Py_write_noraise(errpipe_write, err_msg, strlen(err_msg));
     }
+    _Py_write_noraise(errpipe_write, err_msg, strlen(err_msg));
 }