fsverity: move sysctl registration out of signature.c

Currently the registration of the fsverity sysctls happens in
signature.c, which couples it to CONFIG_FS_VERITY_BUILTIN_SIGNATURES.

This makes it hard to add new sysctls unrelated to builtin signatures.

Also, some users have started checking whether the directory
/proc/sys/fs/verity exists as a way to tell whether fsverity is
supported.  This isn't the intended method; instead, the existence of
/sys/fs/$fstype/features/verity should be checked, or users should just
try to use the fsverity ioctls.  Regardless, it should be made to work
as expected without a dependency on CONFIG_FS_VERITY_BUILTIN_SIGNATURES.

Therefore, move the sysctl registration into init.c.  With
CONFIG_FS_VERITY_BUILTIN_SIGNATURES, nothing changes.  Without it, but
with CONFIG_FS_VERITY, an empty list of sysctls is now registered.

Link: https://lore.kernel.org/r/20230705212743.42180-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/fs/verity/init.c b/fs/verity/init.c
index bcd11d63eb1c..a29f062f6047 100644
--- a/fs/verity/init.c
+++ b/fs/verity/init.c
@@ -9,6 +9,37 @@
 
 #include <linux/ratelimit.h>
 
+#ifdef CONFIG_SYSCTL
+static struct ctl_table_header *fsverity_sysctl_header;
+
+static struct ctl_table fsverity_sysctl_table[] = {
+#ifdef CONFIG_FS_VERITY_BUILTIN_SIGNATURES
+	{
+		.procname       = "require_signatures",
+		.data           = &fsverity_require_signatures,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec_minmax,
+		.extra1         = SYSCTL_ZERO,
+		.extra2         = SYSCTL_ONE,
+	},
+#endif
+	{ }
+};
+
+static void __init fsverity_init_sysctl(void)
+{
+	fsverity_sysctl_header = register_sysctl("fs/verity",
+						 fsverity_sysctl_table);
+	if (!fsverity_sysctl_header)
+		panic("fsverity sysctl registration failed");
+}
+#else /* CONFIG_SYSCTL */
+static inline void fsverity_init_sysctl(void)
+{
+}
+#endif /* !CONFIG_SYSCTL */
+
 void fsverity_msg(const struct inode *inode, const char *level,
 		  const char *fmt, ...)
 {
@@ -36,6 +67,7 @@ static int __init fsverity_init(void)
 	fsverity_check_hash_algs();
 	fsverity_init_info_cache();
 	fsverity_init_workqueue();
+	fsverity_init_sysctl();
 	fsverity_init_signature();
 	return 0;
 }