Re: [syzbot] [fs?] KASAN: use-after-free Read in hpfs_get_ea

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

#syz test

diff --git a/fs/hpfs/Kconfig b/fs/hpfs/Kconfig
index ac1e9318e65a..d3dfbe76be8a 100644
--- a/fs/hpfs/Kconfig
+++ b/fs/hpfs/Kconfig
@@ -15,3 +15,14 @@ config HPFS_FS
 
 	  To compile this file system support as a module, choose M here: the
 	  module will be called hpfs.  If unsure, say N.
+
+config HPFS_FS_ALLOW_NO_ERROR_CHECK_MODE
+	bool "Allow no-error-check mode for maximum speed"
+	depends on HPFS_FS
+	default n
+	help
+	  This option enables check=none mount option. If check=none is
+	  specified, users can expect maximum speed at the cost of minimum
+	  robustness. Sane users should not specify check=none option, for e.g.
+	  use-after-free bug will happen when the filesystem is corrupted or
+	  crafted.
diff --git a/fs/hpfs/super.c b/fs/hpfs/super.c
index 42b779b4d87f..558093b2beab 100644
--- a/fs/hpfs/super.c
+++ b/fs/hpfs/super.c
@@ -285,7 +285,9 @@ static const struct constant_table hpfs_param_case[] = {
 };
 
 static const struct constant_table hpfs_param_check[] = {
+#ifdef CONFIG_HPFS_FS_ALLOW_NO_ERROR_CHECK_MODE
 	{"none",	0},
+#endif
 	{"normal",	1},
 	{"strict",	2},
 	{}