[PATCH 3/3] binfmt_misc: annotate racy accesses to ->enabled

[Christian Brauner <brauner@kernel.org>]

->enabled has always been read and written locklessly: every exec
reads it in load_misc_binary() while bm_status_write() or a concurrent
remount via bm_fill_super() may flip it. That is fine as it is an
independent boolean toggle but the accesses should be marked
accordingly for KCSAN. Annotate them with READ_ONCE()/WRITE_ONCE().

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/binfmt_misc.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 9d1039dcd3f7..0f04709a0a39 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -215,7 +215,7 @@ static int load_misc_binary(struct linux_binprm *bprm)
 	struct binfmt_misc *misc;
 
 	misc = load_binfmt_misc();
-	if (!misc->enabled)
+	if (!READ_ONCE(misc->enabled))
 		return retval;
 
 	fmt = get_binfmt_handler(misc, bprm);
@@ -863,7 +863,7 @@ bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 	char *s;
 
 	misc = i_binfmt_misc(file_inode(file));
-	s = misc->enabled ? "enabled\n" : "disabled\n";
+	s = READ_ONCE(misc->enabled) ? "enabled\n" : "disabled\n";
 	return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
 }
 
@@ -880,11 +880,11 @@ static ssize_t bm_status_write(struct file *file, const char __user *buffer,
 	switch (res) {
 	case 1:
 		/* Disable all handlers. */
-		misc->enabled = false;
+		WRITE_ONCE(misc->enabled, false);
 		break;
 	case 2:
 		/* Enable all handlers. */
-		misc->enabled = true;
+		WRITE_ONCE(misc->enabled, true);
 		break;
 	case 3:
 		/* Delete all handlers. */
@@ -995,7 +995,7 @@ static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
 	 * someone mounts binfmt_misc for the first time or again we simply
 	 * reset ->enabled to true.
 	 */
-	misc->enabled = true;
+	WRITE_ONCE(misc->enabled, true);
 
 	err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
 	if (!err)

-- 
2.53.0