fat: fix using uninitialized fields of fat_inode/fsinfo_inode

Recently fallocate patch was merged and it uses
MSDOS_I(inode)->mmu_private at fat_evict_inode().  However,
fat_inode/fsinfo_inode that was introduced in past didn't initialize
MSDOS_I(inode) properly.

With those combinations, it became the cause of accessing random entry
in FAT area.

Link: http://lkml.kernel.org/r/87pohrj4i8.fsf@mail.parknet.co.jp
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Reported-by: Moreno Bartalucci <moreno.bartalucci@tecnorama.it>
Tested-by: Moreno Bartalucci <moreno.bartalucci@tecnorama.it>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 1 deletions

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 338d2f73eb29..a2c05f2ada6d 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1359,6 +1359,16 @@ out:
         return 0;
 }
 
+static void fat_dummy_inode_init(struct inode *inode)
+{
+        /* Initialize this dummy inode to work as no-op. */
+        MSDOS_I(inode)->mmu_private = 0;
+        MSDOS_I(inode)->i_start = 0;
+        MSDOS_I(inode)->i_logstart = 0;
+        MSDOS_I(inode)->i_attrs = 0;
+        MSDOS_I(inode)->i_pos = 0;
+}
+
 static int fat_read_root(struct inode *inode)
 {
         struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
@@ -1803,12 +1813,13 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
         fat_inode = new_inode(sb);
         if (!fat_inode)
                 goto out_fail;
-        MSDOS_I(fat_inode)->i_pos = 0;
+        fat_dummy_inode_init(fat_inode);
         sbi->fat_inode = fat_inode;
 
         fsinfo_inode = new_inode(sb);
         if (!fsinfo_inode)
                 goto out_fail;
+        fat_dummy_inode_init(fsinfo_inode);
         fsinfo_inode->i_ino = MSDOS_FSINFO_INO;
         sbi->fsinfo_inode = fsinfo_inode;
         insert_inode_hash(fsinfo_inode);