kconfig: Avoid prompting for transitional symbols

The "transitional" symbol keyword, while working with the "olddefconfig"
target, was prompting during "oldconfig". This occurred because these
symbols were not being marked as user-defined when they received values
from transitional symbols that had user values. The "olddefconfig" target
explicitly doesn't prompt for anything, so this deficiency wasn't noticed.

The issue manifested when a symbol's value came from a transitional
symbol's user value but the receiving symbol wasn't marked with
SYMBOL_DEF_USER. Thus the "oldconfig" logic would then prompt for these
symbols unnecessarily.

Check after value calculation whether a symbol without a user value
gets its value from a single transitional symbol that does have a user
value. In such cases, mark the receiving symbol as user-defined to
prevent prompting.

Update regression tests to verify that symbols with transitional defaults
are not prompted in "oldconfig", except when conditional defaults evaluate
to 'no' and should legitimately be prompted.

Build tested with "make testconfig".

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Closes: https://lore.kernel.org/lkml/CAHk-=wgZjUk4Cy2XgNkTrQoO8XCmNUHrTe5D519Fij1POK+3qw@mail.gmail.com/
Fixes: f9afce4f32e9 ("kconfig: Add transitional symbol attribute for migration support")
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Link: https://lore.kernel.org/r/20250930154514.it.623-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/scripts/kconfig/tests/transitional/__init__.py b/scripts/kconfig/tests/transitional/__init__.py
index 61937d10edf1..b50ba2397548 100644
--- a/scripts/kconfig/tests/transitional/__init__.py
+++ b/scripts/kconfig/tests/transitional/__init__.py
@@ -6,6 +6,7 @@ This tests that:
 - OLD_* options in existing .config cause NEW_* options to be set
 - OLD_* options are not written to the new .config file
 - NEW_* options appear in the new .config file with correct values
+- NEW_* options with defaults from transitional symbols are not prompted
 - All Kconfig types work correctly: bool, tristate, string, hex, int
 - User-set NEW values take precedence over conflicting OLD transitional values
 """
@@ -16,3 +17,9 @@ def test(conf):
 
     # Check that the configuration matches expected output
     assert conf.config_contains('expected_config')
+
+    # Test oldconfig to ensure symbols with transitional defaults are not prompted
+    assert conf.oldconfig(dot_config='initial_config', in_keys='n\n') == 0
+
+    # Except for when conditional default evaluates to 'no'
+    assert conf.stdout_contains('expected_stdout')