nilfs2: fix leak of nilfs_root in case of writer thread creation failure

mainline inclusion
from mainline-v6.1-rc1
commit d0d51a97063db4704a5ef6bc978dddab1636a306
category: bugfix
bugzilla: 187884, https://gitee.com/src-openeuler/kernel/issues/I5X2OB
CVE: CVE-2022-3646

--------------------------------

If nilfs_attach_log_writer() failed to create a log writer thread, it
frees a data structure of the log writer without any cleanup.  After
commit e912a5b6 ("nilfs2: use root object to get ifile"), this causes
a leak of struct nilfs_root, which started to leak an ifile metadata inode
and a kobject on that struct.

In addition, if the kernel is booted with panic_on_warn, the above
ifile metadata inode leak will cause the following panic when the
nilfs2 kernel module is removed:

  kmem_cache_destroy nilfs2_inode_cache: Slab cache still has objects when
  called from nilfs_destroy_cachep+0x16/0x3a [nilfs2]
  WARNING: CPU: 8 PID: 1464 at mm/slab_common.c:494 kmem_cache_destroy+0x138/0x140
  ...
  RIP: 0010:kmem_cache_destroy+0x138/0x140
  Code: 00 20 00 00 e8 a9 55 d8 ff e9 76 ff ff ff 48 8b 53 60 48 c7 c6 20 70 65 86 48 c7 c7 d8 69 9c 86 48 8b 4c 24 28 e8 ef 71 c7 00 <0f> 0b e9 53 ff ff ff c3 48 81 ff ff 0f 00 00 77 03 31 c0 c3 53 48
  ...
  Call Trace:
   <TASK>
   ? nilfs_palloc_freev.cold.24+0x58/0x58 [nilfs2]
   nilfs_destroy_cachep+0x16/0x3a [nilfs2]
   exit_nilfs_fs+0xa/0x1b [nilfs2]
    __x64_sys_delete_module+0x1d9/0x3a0
   ? __sanitizer_cov_trace_pc+0x1a/0x50
   ? syscall_trace_enter.isra.19+0x119/0x190
   do_syscall_64+0x34/0x80
   entry_SYSCALL_64_after_hwframe+0x63/0xcd
   ...
   </TASK>
  Kernel panic - not syncing: panic_on_warn set ...

This patch fixes these issues by calling nilfs_detach_log_writer() cleanup
function if spawning the log writer thread fails.

Link: https://lkml.kernel.org/r/20221007085226.57667-1-konishi.ryusuke@gmail.com


Fixes: e912a5b6 ("nilfs2: use root object to get ifile")
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by:  <syzbot+7381dc4ad60658ca4c05@syzkaller.appspotmail.com>
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Conflict:
	fs/nilfs2/segment.c

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>

fs/nilfs2/segment.c

@@ -2781,10 +2781,9 @@ int nilfs_attach_log_writer(struct super_block *sb, struct nilfs_root *root)
 		return -ENOMEM;
 
 	err = nilfs_segctor_start_thread(nilfs->ns_writer);
-	if (err) {
-		kfree(nilfs->ns_writer);
-		nilfs->ns_writer = NULL;
-	}
+	if (unlikely(err))
+		nilfs_detach_log_writer(sb);
+
 	return err;
 }