Linux kernel -stable discussions
 help / color / mirror / Atom feed
* FAILED: patch "[PATCH] fs/ntfs3: use d_instantiate_new() in ntfs_create_inode() and" failed to apply to 5.15-stable tree
@ 2026-09-29  6:44 gregkh
  2026-09-29 14:22 ` [PATCH 5.15.y 1/2] fs/ntfs3: Redesign ntfs_create_inode to return error code instead of inode Sasha Levin
  0 siblings, 1 reply; 3+ messages in thread
From: gregkh @ 2026-09-29  6:44 UTC (permalink / raw)
  To: brauner, jack; +Cc: stable


The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 1abd643f3783ea8f8e273c18697ff0413aa92dc7
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026092906-gestation-filtrate-f5c2@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1abd643f3783ea8f8e273c18697ff0413aa92dc7 Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Wed, 9 Sep 2026 11:03:18 +0200
Subject: [PATCH] fs/ntfs3: use d_instantiate_new() in ntfs_create_inode() and
 murder syzbot's "WARNING in do_new_mount" saga

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 <jack@suse.cz>
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) <brauner@kernel.org>

diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c
index 56b4f6469a28..4ac26c80bd34 100644
--- a/fs/ntfs3/inode.c
+++ b/fs/ntfs3/inode.c
@@ -1866,10 +1866,10 @@ int ntfs_create_inode(struct mnt_idmap *idmap, struct inode *dir,
 		goto out6;
 
 	/*
-	 * 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);
 
 	/* Set original time. inode times (i_ctime) may be changed in ntfs_init_acl. */
 	inode_set_atime_to_ts(inode, ni->i_crtime);
@@ -1917,9 +1917,6 @@ int ntfs_create_inode(struct mnt_idmap *idmap, struct inode *dir,
 	if (!fnd)
 		ni_unlock(dir_ni);
 
-	if (!err)
-		unlock_new_inode(inode);
-
 	return err;
 }
 


^ permalink raw reply related	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2026-09-29 14:22 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-09-29  6:44 FAILED: patch "[PATCH] fs/ntfs3: use d_instantiate_new() in ntfs_create_inode() and" failed to apply to 5.15-stable tree gregkh
2026-09-29 14:22 ` [PATCH 5.15.y 1/2] fs/ntfs3: Redesign ntfs_create_inode to return error code instead of inode Sasha Levin
2026-09-29 14:22   ` [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 Sasha Levin

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox