It makes little sense for fsmount() to output the warning message when
mount_too_revealing() is violated to kmsg. Instead, the warning should
be output (with a "VFS" prefix) to the fscontext log. In addition,
include the same log message for mount_too_revealing() when doing a
regular mount for consistency.

With the newest fsopen()-based mount(8) from util-linux, the error
messages now look like

  # mount -t proc proc /tmp
  mount: /tmp: fsmount() failed: VFS: Mount too revealing.
         dmesg(1) may have more information after failed mount system call.

which could finally result in mount_too_revealing() errors being easier
for users to detect and understand.

Signed-off-by: Aleksa Sarai <redacted>
---
 fs/namespace.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 55f28cebbe7d..1e1c2c257e2e 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c

@@ -3820,8 +3820,10 @@ static int do_new_mount_fc(struct fs_context *fc, struct path *mountpoint,
 	int error;
 
 	error = security_sb_kern_mount(sb);
-	if (!error && mount_too_revealing(sb, &mnt_flags))
+	if (!error && mount_too_revealing(sb, &mnt_flags)) {
+		errorfcp(fc, "VFS", "Mount too revealing");
 		error = -EPERM;
+	}
 
 	if (unlikely(error)) {
 		fc_drop_locked(fc);

@@ -4547,7 +4549,7 @@ SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags,
 
 	ret = -EPERM;
 	if (mount_too_revealing(fc->root->d_sb, &mnt_flags)) {
-		pr_warn("VFS: Mount too revealing\n");
+		errorfcp(fc, "VFS", "Mount too revealing");
 		goto err_unlock;
 	}
 

-- 
2.50.1