linux-kernel - Forwarded: [PATCH] isofs: fix inode leak caused by disconnected dentries from exportfs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <68dced58.050a0220.25d7ab.0774.GAE@google.com>
Date: Wed, 01 Oct 2025 01:59:04 -0700
From: syzbot <syzbot+1d79ebe5383fc016cf07@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Forwarded: [PATCH] isofs: fix inode leak caused by disconnected
 dentries from exportfs

For archival purposes, forwarding an incoming command email to
linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com.

***

Subject: [PATCH] isofs: fix inode leak caused by disconnected dentries from exportfs
Author: kartikey406@...il.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

When open_by_handle_at() is used with iso9660 filesystems, exportfs
creates disconnected dentries during file handle resolution. If the
operation fails (e.g., with -ESTALE during reconnect_path()), these
dentries remain cached with their associated inodes.

During unmount, shrink_dcache_for_umount() does not fully evict these
disconnected dentries, leaving their inodes with non-zero reference
counts. This triggers the "VFS: Busy inodes after unmount" warning
and causes inode leaks that accumulate across mount/unmount cycles.

The issue occurs because:
1. open_by_handle_at() calls exportfs_decode_fh_raw() to resolve
   file handles
2. For iso9660 with Joliet extensions, this creates disconnected
   dentries for both primary (iso9660) and secondary (Joliet) root
   inodes
3. When path reconnection fails with -ESTALE, the dentries are left
   in DCACHE_DISCONNECTED state
4. shrink_dcache_for_umount() in generic_shutdown_super() does not
   aggressively evict these disconnected dentries
5. The associated inodes (typically root inodes 1792 and 1807)
   remain with i_count=1, triggering the busy inode check

Add explicit shrink_dcache_sb() call in isofs_put_super() to ensure
all cached dentries, including disconnected ones created by exportfs
operations, are released before the superblock is destroyed.

Reported-by: syzbot+1d79ebe5383fc016cf07@...kaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@...il.com>
---
 fs/isofs/inode.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/isofs/inode.c b/fs/isofs/inode.c
index 6f0e6b19383c..bee410705442 100644
--- a/fs/isofs/inode.c
+++ b/fs/isofs/inode.c
@@ -52,6 +52,7 @@ static int isofs_dentry_cmp_ms(const struct dentry *dentry,
 static void isofs_put_super(struct super_block *sb)
 {
 	struct isofs_sb_info *sbi = ISOFS_SB(sb);
+	shrink_dcache_sb(sb);

 #ifdef CONFIG_JOLIET
 	unload_nls(sbi->s_nls_iocharset);
-- 
2.43.0