Re: [PATCH 5/5] fs: Convert struct file::f_count to refcount_long_t

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To: Kees Cook <keescook@xxxxxxxxxxxx>
Subject: Re: [PATCH 5/5] fs: Convert struct file::f_count to refcount_long_t
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Thu, 2 May 2024 23:42:50 +0100
Cc: Christian Brauner <brauner@xxxxxxxxxx>, Jan Kara <jack@xxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, Zack Rusin <zack.rusin@xxxxxxxxxxxx>, Broadcom internal kernel review list <bcm-kernel-feedback-list@xxxxxxxxxxxx>, Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>, Maxime Ripard <mripard@xxxxxxxxxx>, Thomas Zimmermann <tzimmermann@xxxxxxx>, David Airlie <airlied@xxxxxxxxx>, Daniel Vetter <daniel@xxxxxxxx>, Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>, Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>, Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>, Tvrtko Ursulin <tursulin@xxxxxxxxxxx>, Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>, Lucas De Marchi <lucas.demarchi@xxxxxxxxx>, Matt Atwood <matthew.s.atwood@xxxxxxxxx>, Matthew Auld <matthew.auld@xxxxxxxxx>, Nirmoy Das <nirmoy.das@xxxxxxxxx>, Jonathan Cavitt <jonathan.cavitt@xxxxxxxxx>, Will Deacon <will@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Boqun Feng <boqun.feng@xxxxxxxxx>, Mark Rutland <mark.rutland@xxxxxxx>, Kent Overstreet <kent.overstreet@xxxxxxxxx>, Masahiro Yamada <masahiroy@xxxxxxxxxx>, Nathan Chancellor <nathan@xxxxxxxxxx>, Nicolas Schier <nicolas@xxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, dri-devel@xxxxxxxxxxxxxxxxxxxxx, intel-gfx@xxxxxxxxxxxxxxxxxxxxx, linux-kbuild@xxxxxxxxxxxxxxx, linux-hardening@xxxxxxxxxxxxxxx
In-reply-to: <20240502223341.1835070-5-keescook@chromium.org>

On Thu, May 02, 2024 at 03:33:40PM -0700, Kees Cook wrote:
> Underflow of f_count needs to be more carefully detected than it
> currently is. The results of get_file() should be checked, but the
> first step is detection. Redefine f_count from atomic_long_t to
> refcount_long_t.

	It is used on fairly hot paths.  What's more, it's not
at all obvious what the hell would right semantics be.

NAKed-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

Follow-Ups:
- Re: [PATCH 5/5] fs: Convert struct file::f_count to refcount_long_t
  - From: Kees Cook

References:
- [PATCH 0/5] fs: Do not allow get_file() to resurrect 0 f_count
  - From: Kees Cook
- [PATCH 5/5] fs: Convert struct file::f_count to refcount_long_t
  - From: Kees Cook

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