linux-kernel - [PATCH 1/2] Fix userfaultfd_api to return EINVAL as expected

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Date: Tue,  7 May 2024 15:55:09 -0400
From: Audra Mitchell <audra@...hat.com>
To: viro@...iv.linux.org.uk
Cc: brauner@...nel.org,
	jack@...e.cz,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org,
	shuah@...nel.org,
	linux-kselftest@...r.kernel.org,
	linux-mm@...ck.org,
	raquini@...hat.com
Subject: [PATCH 1/2] Fix userfaultfd_api to return EINVAL as expected

Currently if we request a feature that is not set in the Kernel
config we fail silently and return the available features. However, the
documentation indicates we should return an EINVAL.

We need to fix this issue since we can end up with a Kernel warning
should a program request the feature UFFD_FEATURE_WP_UNPOPULATED on
a kernel with the config not set with this feature.

Signed-off-by: Audra Mitchell <audra@...hat.com>
---
 fs/userfaultfd.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 60dcfafdc11a..17210558de79 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -2073,6 +2073,11 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
 	uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
 	uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC;
 #endif
+
+	ret = -EINVAL;
+	if (features & ~uffdio_api.features)
+		goto err_out;
+
 	uffdio_api.ioctls = UFFD_API_IOCTLS;
 	ret = -EFAULT;
 	if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
-- 
2.44.0