linux-kernel - [PATCH v2 1/3] Fix userfaultfd_api to return EINVAL as expected

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Date: Fri, 21 Jun 2024 14:12:22 -0400
From: Audra Mitchell <audra@...hat.com>
To: viro@...iv.linux.org.uk
Cc: brauner@...nel.org,
	jack@...e.cz,
	aarcange@...hat.com,
	akpm@...ux-foundation.org,
	rppt@...ux.vnet.ibm.com,
	shli@...com,
	peterx@...hat.com,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	shuah@...nel.org,
	linux-kselftest@...r.kernel.org,
	raquini@...hat.com
Subject: [PATCH v2 1/3] 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 all the available features. However,
the man page 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.

 [  200.812896] WARNING: CPU: 91 PID: 13634 at mm/memory.c:1660 zap_pte_range+0x43d/0x660
 [  200.820738] Modules linked in:
 [  200.869387] CPU: 91 PID: 13634 Comm: userfaultfd Kdump: loaded Not tainted 6.9.0-rc5+ #8
 [  200.877477] Hardware name: Dell Inc. PowerEdge R6525/0N7YGH, BIOS 2.7.3 03/30/2022
 [  200.885052] RIP: 0010:zap_pte_range+0x43d/0x660

Fixes: e06f1e1dd499 ("userfaultfd: wp: enabled write protection in userfaultfd API")
Signed-off-by: Audra Mitchell <audra@...hat.com>
---
 fs/userfaultfd.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index eee7320ab0b0..17e409ceaa33 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -2057,7 +2057,7 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
 		goto out;
 	features = uffdio_api.features;
 	ret = -EINVAL;
-	if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES))
+	if (uffdio_api.api != UFFD_API)
 		goto err_out;
 	ret = -EPERM;
 	if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
@@ -2081,6 +2081,11 @@ 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