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

Link: https://lkml.kernel.org/r/20240626130513.120193-1-audra@redhat.com
Fixes: e06f1e1dd499 ("userfaultfd: wp: enabled write protection in userfaultfd API")
Signed-off-by: Audra Mitchell <audra@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rafael Aquini <raquini@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index eee7320ab0b028c31676a6f8e59f9748fecc9671..17e409ceaa3366687d92080abe4a055e5d178482 100644 (file)
--- 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)))