[PATCH 4.18 157/158] autofs: fix autofs_sbi() does not check super block type

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ian Kent <raven@xxxxxxxxxx>

commit 0633da48f0793aeba27f82d30605624416723a91 upstream.

autofs_sbi() does not check the superblock magic number to verify it has
been given an autofs super block.

Link: http://lkml.kernel.org/r/153475422934.17131.7563724552005298277.stgit@xxxxxxxxxxxxxxxx
Reported-by: <syzbot+87c3c541582e56943277@xxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Guenter Roeck <groeck@xxxxxxxxxx>
Cc: Zubin Mithra <zsm@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/autofs/autofs_i.h |    4 +++-
 fs/autofs/inode.c    |    1 -
 2 files changed, 3 insertions(+), 2 deletions(-)

--- a/fs/autofs/autofs_i.h
+++ b/fs/autofs/autofs_i.h
@@ -26,6 +26,7 @@
 #include <linux/list.h>
 #include <linux/completion.h>
 #include <linux/file.h>
+#include <linux/magic.h>
 
 /* This is the range of ioctl() numbers we claim as ours */
 #define AUTOFS_IOC_FIRST     AUTOFS_IOC_READY
@@ -124,7 +125,8 @@ struct autofs_sb_info {
 
 static inline struct autofs_sb_info *autofs_sbi(struct super_block *sb)
 {
-	return (struct autofs_sb_info *)(sb->s_fs_info);
+	return sb->s_magic != AUTOFS_SUPER_MAGIC ?
+		NULL : (struct autofs_sb_info *)(sb->s_fs_info);
 }
 
 static inline struct autofs_info *autofs_dentry_ino(struct dentry *dentry)
--- a/fs/autofs/inode.c
+++ b/fs/autofs/inode.c
@@ -10,7 +10,6 @@
 #include <linux/seq_file.h>
 #include <linux/pagemap.h>
 #include <linux/parser.h>
-#include <linux/magic.h>
 
 #include "autofs_i.h"