fat: fix uninit-memory access for partial initialized inode

When get an error in the middle of reading an inode, some fields in the
inode might be still not initialized.  And then the evict_inode path may
access those fields via iput().

To fix, this makes sure that inode fields are initialized.

Reported-by: syzbot+9d82b8de2992579da5d0@syzkaller.appspotmail.com
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/871rqnreqx.fsf@mail.parknet.co.jp
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 594b05ae16c9bf04584ae9c6c4dba50dbdecffcb..71946da8438849859b5240d199b216cf0b424f55 100644 (file)
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -750,6 +750,13 @@ static struct inode *fat_alloc_inode(struct super_block *sb)
                return NULL;
 
        init_rwsem(&ei->truncate_lock);
+       /* Zeroing to allow iput() even if partial initialized inode. */
+       ei->mmu_private = 0;
+       ei->i_start = 0;
+       ei->i_logstart = 0;
+       ei->i_attrs = 0;
+       ei->i_pos = 0;
+
        return &ei->vfs_inode;
 }
 
@@ -1374,16 +1381,6 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
        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);
@@ -1844,13 +1841,11 @@ 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;
-       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);