linux-kernel - Re: [PATCH] btrfs: fix signedness issue in min()

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-prev] [day] [month] [year] [list]

Message-ID: <20250317192638.GA32661@twin.jikos.cz>
Date: Mon, 17 Mar 2025 20:26:39 +0100
From: David Sterba <dsterba@...e.cz>
To: David Laight <david.laight.linux@...il.com>
Cc: Arnd Bergmann <arnd@...nel.org>, Chris Mason <clm@...com>,
	Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
	Qu Wenruo <wqu@...e.com>, Arnd Bergmann <arnd@...db.de>,
	Johannes Thumshirn <johannes.thumshirn@....com>,
	Filipe Manana <fdmanana@...e.com>, Li Zetao <lizetao1@...wei.com>,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] btrfs: fix signedness issue in min()

On Mon, Mar 17, 2025 at 02:16:37PM +0000, David Laight wrote:
> On Fri, 14 Mar 2025 16:54:41 +0100
> Arnd Bergmann <arnd@...nel.org> wrote:
> 
> > From: Arnd Bergmann <arnd@...db.de>
> > 
> > Comparing a u64 to an loff_t causes a warning in min()
> > 
> > fs/btrfs/extent_io.c: In function 'extent_write_locked_range':
> > include/linux/compiler_types.h:557:45: error: call to '__compiletime_assert_588' declared with attribute error: min(folio_pos(folio) + folio_size(folio) - 1, end) signedness error
> > fs/btrfs/extent_io.c:2472:27: note: in expansion of macro 'min'
> >  2472 |                 cur_end = min(folio_pos(folio) + folio_size(folio) - 1, end);
> >       |                           ^~~
> > 
> > Use min_t() instead.
> 
> It would be slightly better to use min_unsigned() since, regardless of the types
> involved, it can't discard significant bits.
> 
> OTOH the real problem here is that both folio_pos() and folio_size() return signed types.

folio_size() returns size_t:

static inline size_t folio_size(const struct folio *folio)
{
	return PAGE_SIZE << folio_order(folio);
}

Otherwise the min_t with force u64 is ok and lots of min() use (in
btrfs) was converted to the typed variant in case the types don't match.