+ nilfs2-fix-leak-of-nilfs_root-in-case-of-writer-thread-creation-failure.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: nilfs2: fix leak of nilfs_root in case of writer thread creation failure
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     nilfs2-fix-leak-of-nilfs_root-in-case-of-writer-thread-creation-failure.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/nilfs2-fix-leak-of-nilfs_root-in-case-of-writer-thread-creation-failure.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Subject: nilfs2: fix leak of nilfs_root in case of writer thread creation failure
Date: Fri, 7 Oct 2022 17:52:26 +0900

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 e912a5b66837 ("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: e912a5b66837 ("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>
---

 fs/nilfs2/segment.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/fs/nilfs2/segment.c~nilfs2-fix-leak-of-nilfs_root-in-case-of-writer-thread-creation-failure
+++ a/fs/nilfs2/segment.c
@@ -2786,10 +2786,9 @@ int nilfs_attach_log_writer(struct super
 	inode_attach_wb(nilfs->ns_bdev->bd_inode, NULL);
 
 	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;
 }
 
_

Patches currently in -mm which might be from konishi.ryusuke@gmail.com are

nilfs2-fix-use-after-free-bug-of-struct-nilfs_root.patch
nilfs2-fix-null-pointer-dereference-at-nilfs_bmap_lookup_at_level.patch
nilfs2-fix-leak-of-nilfs_root-in-case-of-writer-thread-creation-failure.patch
nilfs2-replace-warn_ons-by-nilfs_error-for-checkpoint-acquisition-failure.patch