squashfs: verify inode mode when loading from disk

The inode mode loaded from corrupted disk might by error contain the file
type bits.  Since the file type bits are set by squashfs_read_inode()
using bitwise OR, the file type bits must not be set by
squashfs_new_inode() from squashfs_read_inode(); otherwise, an invalid
file type bits later confuses may_open().

Link: https://lkml.kernel.org/r/f63d8d11-2254-4fc3-9292-9a43a93b374e@I-love.SAKURA.ne.jp
Reported-by: syzbot <syzbot+895c23f6917da440ed0d@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=895c23f6917da440ed0d
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Phillip Lougher <phillip@squashfs.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/squashfs/inode.c b/fs/squashfs/inode.c
index d5918eba27e3711f62d7b4b8a1d7972f22ac6ca5..dee8fa01693077606c8444325b0aface4f635d72 100644 (file)
--- a/fs/squashfs/inode.c
+++ b/fs/squashfs/inode.c
@@ -68,6 +68,10 @@ static int squashfs_new_inode(struct super_block *sb, struct inode *inode,
        inode->i_mode = le16_to_cpu(sqsh_ino->mode);
        inode->i_size = 0;
 
+       /* File type must not be set at this moment, for it will later be set by the caller. */
+       if (inode->i_mode & S_IFMT)
+               err = -EIO;
+
        return err;
 }