From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D5B0F3D3D09 for ; Tue, 29 Sep 2026 14:22:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790691777; cv=none; b=u/zhgpbUU7BoIRliBJrQGd9UDT7kVJugB/cMn0HH1r7+E+c3F/ZSzLIfECFpAc272TseRjHao3Qjv6NLhU8aZsaIKoP3kPixnGlwIwgQsh/kASTkjpits+oRGZL5ehrUwOMJSDAeWpVzSipaEgkzNmSccWP/T2gqAYhbBOuUN04= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790691777; c=relaxed/simple; bh=A3733s++VR5UMvYQGfdiOY3txdqAG8OiDpEdc6OIWnU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=i54/b69Vql8LiMubFILBAzF+rsgps0+J9BndkCHttEcTiCaTcf/hBNPLDNOJs5zHYuU4Eufa4OHSyVjqx6aH1b6OMGgGbNRBK7ZzLD0+xg/QGJvhEPgP2BOu2qjVhmDiDQOjqiTZYy/YZcIyUNTU0fRP7iPH0IJkXBA99hU1IvA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LXJWkmHk; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LXJWkmHk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2F19B1F00893; Tue, 29 Sep 2026 14:22:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790691775; bh=aXbBnJOmA4PClLu1h1uhEx0vbFa/nLHbetIvEFtZTtg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=LXJWkmHkEtOYS6d+Rd8LYfzPoui2SNzprsnU3Y3DTp2RkCxrKY6b7HYcf5SaNp2HU YRJduzVdCx3WahUCTxCyy6iKi78xg1rCUW/crHfCdsrPTeSa0JQO44QJ7mmzfIQA1Z d9FF3/G4kk1LcXRnsUvxeEnK5r4GDCTDKII/k2J0LbU6rz8LxqD6GPfu3TxOQHQSCp CBadNs1PBEUmUPB/Ft5Y5pxrP86UZqAp5Rdr0v9O7PaZmUgKq5l+w/gwnbAYVWiNmT c39ZsCYdmuWiklzrIWav/guBblsNYwkQEIYr0PWsNrueChgjNXf7QrMI+eyY72myHQ OTV8oG0Cjjnjw== From: Sasha Levin To: stable@vger.kernel.org Cc: Christian Brauner , Jan Kara , syzbot+2a13ad6914e6fcec716c@syzkaller.appspotmail.com, Sasha Levin Subject: [PATCH 5.15.y 2/2] fs/ntfs3: use d_instantiate_new() in ntfs_create_inode() and murder syzbot's "WARNING in do_new_mount" saga Date: Tue, 29 Sep 2026 10:22:53 -0400 Message-ID: <20260929142253.3582339-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260929142253.3582339-1-sashal@kernel.org> References: <2026092906-gestation-filtrate-f5c2@gregkh> <20260929142253.3582339-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Christian Brauner [ Upstream commit 1abd643f3783ea8f8e273c18697ff0413aa92dc7 ] ntfs_create_inode() creates a new inode via ntfs_new_inode(). It hashes it with insert_inode_locked() and so it's marked as I_NEW until unlock_new_inode(). ntfs 3 calls d_instantiate() in between though... Since the dentry was already hashed by the lookup before the create any path walk finds it without touching the parent's i_rwsem and so can lock the inode. If the inode is a directory unlock_new_inode() calls lockdep_annotate_inode_mutex_key() and marks i_rwsem with the i_mutex_dir_key class. That resets the count and the owner of a lock somebody else may already hold by now... syzbot has been spamming us with the same godforsaken bug "WARNING in do_new_mount" since 2023. I can't take it anymore so I went looking. Afaict, syzbot's executor chdirs into a freshly mounted ntfs3 image, creates a directory and then mounts some pseudofs on it. Everytime the mkdir() takes longer than syzbot waits mount() runs concurrently: mkdir("./sys") mount(NULL, "./sys", "sysfs") ntfs_create_inode() d_instantiate() user_path_at() finds the dentry do_lock_mount() inode_lock(inode) namespace_lock() unlock_new_inode() lockdep_annotate_inode_mutex_key() init_rwsem(&inode->i_rwsem) unlock_mount() inode_unlock(inode) The mount side then releases a lock that according to the rwsem nobody holds: DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) && ...): count = 0x0, magic = 0xffff888043a854e8, owner = 0x0, curr 0xffff888000244880, list empty WARNING: CPU: 0 PID: 5346 at kernel/locking/rwsem.c:1368 __up_write Call Trace: inode_unlock include/linux/fs.h:877 [inline] unlock_mount fs/namespace.c:2892 [inline] do_new_mount_fc fs/namespace.c:3828 [inline] do_new_mount+0x777/0xa40 fs/namespace.c:3887 On PREEMPT_RT the same thing shows up as DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current) WARNING: kernel/locking/rtmutex_common.h:193 at rt_mutex_slowunlock The up_write() underflows the reset count. A following inode_lock() on that directory then never returns. A path walk into the new directory racing with the mkdir() corrupts the lock the same way via inode_lock_shared() in lookup_slow(). Switch to d_instantiate_new() and drop the trailing unlock_new_inode(). All error paths bail out before that point with I_NEW still set and keep using discard_new_inode(). May we never see this fscking bug report again. Link: https://patch.msgid.link/20260909-work-ntfs3-d_instantiate_new-v1-1-2db697162ce8@kernel.org Fixes: 82cae269cfa9 ("fs/ntfs3: Add initialization of super block") Reviewed-by: Jan Kara Cc: stable@vger.kernel.org # v5.15+ Reported-by: syzbot+2a13ad6914e6fcec716c@syzkaller.appspotmail.com Closes: https://lore.kernel.org/6a9beced.a5e650b3.26d8a.000b.GAE@google.com Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Sasha Levin --- fs/ntfs3/inode.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c index 243791cc3c529..9e4a0afabf691 100644 --- a/fs/ntfs3/inode.c +++ b/fs/ntfs3/inode.c @@ -1634,10 +1634,10 @@ int ntfs_create_inode(struct user_namespace *mnt_userns, struct inode *dir, } /* - * Call 'd_instantiate' after inode->i_op is set + * Call 'd_instantiate_new' after inode->i_op is set * but before finish_open. */ - d_instantiate(dentry, inode); + d_instantiate_new(dentry, inode); ntfs_save_wsl_perm(inode); mark_inode_dirty(dir); @@ -1677,9 +1677,6 @@ int ntfs_create_inode(struct user_namespace *mnt_userns, struct inode *dir, if (err) ni_unlock(dir_ni); - if (!err) - unlock_new_inode(inode); - return err; } -- 2.53.0