linux-kernel - [PATCH] fs: Work around NFS wreckage

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-next>] [day] [month] [year] [list]

Date:	Thu, 13 Jan 2011 14:54:30 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Nick Piggin <npiggin@...nel.dk>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, u.kleine-koenig@...gutronix.de,
	"Ramirez Luna, Omar" <omar.ramirez@...com>
Subject: [PATCH] fs: Work around NFS wreckage

The dcache scalability work broke NFS root filesystems.

"cd /" results in the following problem:

    link_path_walk("/",...);
	jumps to return_reval
	need_reval_dot() returns true for NFS
	d_revalidate()
		dentry->d_op->d_revalidate(dentry, nd);
		 	returns -ECHILD due to nd->flags & LOOKUP_RCU
		nameidata_dentry_drop_rcu()
			spin_lock(&parent->d_lock);
			spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);

			This deadlocks because dentry == parent

This problem exists for any filesystem which implements d_revalidate.

Uwe bisected is down to commit 34286d6(fs: rcu-walk aware d_revalidate
method), but reverting that patch causes different wreckage to show up.

Check for parent equal dentry and skip the nested lock to avoid the
deadlock. I'm sure this is the wrong fix, but at least it "works" :)

Reported-by: Uwe Kleine-Koenig <u.kleine-koenig@...gutronix.de>
Reported-by: "Ramirez Luna, Omar" <omar.ramirez@...com>
Not-Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 fs/namei.c |    4 ++++
 1 file changed, 4 insertions(+)

Index: linux-2.6/fs/namei.c
===================================================================
--- linux-2.6.orig/fs/namei.c
+++ linux-2.6/fs/namei.c
@@ -487,6 +487,8 @@ static int nameidata_dentry_drop_rcu(str
 			goto err_root;
 	}
 	spin_lock(&parent->d_lock);
+	if (parent == dentry)
+		goto same;
 	spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
 	if (!__d_rcu_to_refcount(dentry, nd->seq))
 		goto err;
@@ -499,6 +501,8 @@ static int nameidata_dentry_drop_rcu(str
 	BUG_ON(!parent->d_count);
 	parent->d_count++;
 	spin_unlock(&dentry->d_lock);
+
+same:
 	spin_unlock(&parent->d_lock);
 	if (nd->root.mnt) {
 		path_get(&nd->root);
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/