ubifs: ubifs_symlink: Fix memleak of inode->i_link in error path

ubifs: ubifs_symlink: Fix memleak of inode->i_link in error path

commit 1e022216dcd248326a5bb95609d12a6815bca4e2 upstream.

For error handling path in ubifs_symlink(), inode will be marked as
bad first, then iput() is invoked. If inode->i_link is initialized by
fscrypt_encrypt_symlink() in encryption scenario, inode->i_link won't
be freed by callchain ubifs_free_inode -> fscrypt_free_inode in error
handling path, because make_bad_inode() has changed 'inode->i_mode' as
'S_IFREG'.
Following kmemleak is easy to be reproduced by injecting error in
ubifs_jnl_update() when doing symlink in encryption scenario:
 unreferenced object 0xffff888103da3d98 (size 8):
  comm "ln", pid 1692, jiffies 4294914701 (age 12.045s)
  backtrace:
   kmemdup+0x32/0x70
   __fscrypt_encrypt_symlink+0xed/0x1c0
   ubifs_symlink+0x210/0x300 [ubifs]
   vfs_symlink+0x216/0x360
   do_symlinkat+0x11a/0x190
   do_syscall_64+0x3b/0xe0
There are two ways fixing it:
 1. Remove make_bad_inode() in error handling path. We can do that
    because ubifs_evict_inode() will do same processes for good
    symlink inode and bad symlink inode, for inode->i_nlink checking
    is before is_bad_inode().
 2. Free inode->i_link before marking inode bad.
Method 2 is picked, it has less influence, personally, I think.

Cc: stable@vger.kernel.org
Fixes: 2c58d548f570 ("fscrypt: cache decrypted symlink target in ->i_link")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Suggested-by: Eric Biggers <ebiggers@kernel.org>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>