[PATCH 6.18.y] rust: bug: pass TAINT_WARN to warn_slowpath_fmt() on UML

[Sasha Levin <sashal@kernel.org>]

From: FUJITA Tomonori <fujita.tomonori@gmail.com>

[ Upstream commit 951d09ca450ca76a695016ea76c3fa653bd20439 ]

On UML, `warn_flags!` calls `warn_slowpath_fmt()` directly. Its third
argument is a taint number, but `warn_on!` passes its bug flags there.

As a result, `add_taint()` gets 2304 instead of 9 (`TAINT_WARN`). The
warning is not recorded: `/proc/sys/kernel/tainted` stays 0 after
`warn_on!` fires, where it should be 512. It also causes an
out-of-bounds write in `add_taint()`.

Pass `TAINT_WARN` directly, as C does on UML.

Cc: stable@vger.kernel.org
Fixes: dff64b072708 ("rust: Add warn_on macro")
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Link: https://patch.msgid.link/20261001123103.2198104-1-tomo@flapping.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
[ sashal: adapted warning handling to the single-argument warn_flags! macro and existing CStr API ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 rust/kernel/bug.rs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/bug.rs b/rust/kernel/bug.rs
index 15a84e553fd4d..7e540954d67a0 100644
--- a/rust/kernel/bug.rs
+++ b/rust/kernel/bug.rs
@@ -79,13 +79,17 @@ macro_rules! warn_flags {
 #[cfg(all(CONFIG_BUG, CONFIG_UML))]
 macro_rules! warn_flags {
     ($flags:expr) => {
+        if false {
+            _ = $flags;
+        }
+
         // SAFETY: It is always safe to call `warn_slowpath_fmt()`
         // with a valid null-terminated string.
         unsafe {
             $crate::bindings::warn_slowpath_fmt(
-                $crate::str::CStrExt::as_char_ptr($crate::c_str!(::core::file!())),
+                $crate::str::CStr::as_char_ptr($crate::c_str!(::core::file!())),
                 line!() as $crate::ffi::c_int,
-                $flags as $crate::ffi::c_uint,
+                $crate::bindings::TAINT_WARN,
                 ::core::ptr::null(),
             );
         }
-- 
2.53.0