CVE-2024-26972

In the Linux kernel, the following vulnerability has been resolved:

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

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.