From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 D7BC61B4F2C; Wed, 22 Apr 2026 14:05:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776866710; cv=none; b=gmjvdZQFQgea8HIz2bE5VFvdOwIDyfzMnxyVevuLX9ygpQCPPU5b1SBXu3qEpcmoxjNnt4Sl+fDXI5BjyollJ8hBzr3m9OdVlzpEn1672MO8lXgqDfsVxpXngqnRemwBebodwkxTJxDkpH67756d65DxN9SEz8EJ18yPoMsdyn4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776866710; c=relaxed/simple; bh=NbjZnhjiAQ8jZ9S7U3OSMPwxS22ZcyAHCJqm7H8UFDE=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=EvTGLcnHpU+Yyhx83fK/v8SG8VwJ6Rp3R6whlnK67TcVI5xQrbLGpKgRiTR653lVLIcHQ3M7LodkFEZrSLOHXviCO3bYzV5Tku7EqrPO5WMFiLLX7G0GPLzLmWhKYNkmakh55SEe7ayyuKm0xM+jfTsDnASCeqg/52bRDpXijMo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gjuizzAU; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="gjuizzAU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4CCFEC19425; Wed, 22 Apr 2026 14:05:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776866710; bh=NbjZnhjiAQ8jZ9S7U3OSMPwxS22ZcyAHCJqm7H8UFDE=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=gjuizzAUqMwHw0IAKx0buSzuEX+GQz8g31mPDUWgr42Y//SYyafq0zu/H9rnSaivC UoSiBcuQw5ssyNlNsJ0OdhESdjuLuKW10ty1TlwMAkW+w2c3/oYsF3AVTgnBCBK/8/ qNfR0IFm7/GDj7X44Hu8sCnOkwfeT7sL92dN/KyR29thBbOd+C08/eyeTR7lRF/B4b JgzgE+yRFjU0MaWSuAN0r0LVe+UhvbKRl01QVF951TrFokuI6xMZVB7KAYyh42iNvF VuW36GtVj0faPByDsTse06PCK/v4Z8t9ou5bmukbHZFMAMSXRCzjFbFZbebtku8xVe 85sJ7i2aIklbA== Message-ID: <4ed24d78ed22224b8eee03fbe72a604f534c1509.camel@kernel.org> Subject: Re: [PATCH] dcache: add extra sanity checks of the dentry in dentry_free() From: Jeff Layton To: Christian Brauner Cc: Alexander Viro , Jan Kara , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 22 Apr 2026 10:05:07 -0400 In-Reply-To: <20260422-modebranche-vierundzwanzig-f4e000dee32c@brauner> References: <20260422-dcache-warn-v1-1-50155e1b40b6@kernel.org> <20260422-modebranche-vierundzwanzig-f4e000dee32c@brauner> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Wed, 2026-04-22 at 15:06 +0200, Christian Brauner wrote: > On Wed, Apr 22, 2026 at 07:29:48AM -0400, Jeff Layton wrote: > > If d_flags isn't what we expect, then it's good to display it. Add a ne= w > > DENTRY_WARN_ONCE() macro that also displays d_flags for the dentry. > > Change D_FLAG_VERIFY() to call that instead of a generic WARN_ON_ONCE()= . > >=20 > > Change the existing hlist_unhashed() check in dentry_free() to use the > > new macro, and add checks for other invariants of a dead dentry. Notabl= y: > >=20 > > 1) Ensure that DCACHE_LRU_LIST and DCACHE_SHRINK_LIST are not set. > >=20 > > 2) Ensure that d_lockref is negative > >=20 > > Signed-off-by: Jeff Layton > > --- > > While chatting with Al about this elusive UAF problem, we both noted > > that it would be nice to know what d_flags are when these warnings pop. > > This adds that, and checks for some other invariants in dentry_free(). > > --- > > fs/dcache.c | 10 ++++++++-- > > 1 file changed, 8 insertions(+), 2 deletions(-) > >=20 > > diff --git a/fs/dcache.c b/fs/dcache.c > > index 2c61aeea41f4..210df5c0a1f0 100644 > > --- a/fs/dcache.c > > +++ b/fs/dcache.c > > @@ -426,9 +426,16 @@ static inline void __d_clear_type_and_inode(struct= dentry *dentry) > > this_cpu_inc(nr_dentry_negative); > > } > > =20 > > +#define DENTRY_WARN_ONCE(condition, dentry) \ > > + WARN_ONCE((condition), "dentry=3D%p d_flags=3D0x%x\n", (dentry), (den= try)->d_flags) > > +#define D_FLAG_VERIFY(dentry, x) \ > > + DENTRY_WARN_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRIN= K_LIST)) !=3D (x), (dentry)) >=20 > Would be nice if we had a bunch of dentry debug assert macros in > vfsdebug.h like we have for VFS_BUG_ON_INODE()/VFS_WARN_ON_INODE() in > general imo. Good point. I guess I should have called this VFS_WARN_ON_DENTRY(). There are some other existing warnings in dcache.c that could be converted to use this too. --=20 Jeff Layton