From: Eric Biggers <ebiggers@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Yongpeng Yang <yangyongpeng.storage@gmail.com>,
Jaegeuk Kim <jaegeuk@kernel.org>, Theodore Ts'o <tytso@mit.edu>,
linux-fscrypt@vger.kernel.org,
Yongpeng Yang <yangyongpeng@xiaomi.com>,
linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
Luis Chamberlain <mcgrof@kernel.org>
Subject: Re: [PATCH v2] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT
Date: Tue, 4 Nov 2025 10:10:06 -0800 [thread overview]
Message-ID: <20251104181006.GC1780@sol> (raw)
In-Reply-To: <aQnftXAg93-4FbaO@infradead.org>
On Tue, Nov 04, 2025 at 03:12:53AM -0800, Christoph Hellwig wrote:
> On Mon, Nov 03, 2025 at 08:48:29AM -0800, Eric Biggers wrote:
> > > *inode_ret = inode;
> > > - *lblk_num_ret = ((u64)folio->index << (PAGE_SHIFT - inode->i_blkbits)) +
> > > + *lblk_num_ret = (((u64)folio->index << PAGE_SHIFT) >> inode->i_blkbits) +
>
> This should be using folio_pos() instead of open coding the arithmetics.
Well, folio_pos() doesn't work with sizes greater than S64_MAX, and it
uses multiplication rather than a shift.
Probably doesn't matter, but I always feel like I have to actually check
that.
It looks like the size of block device can come from several different
places, including set_capacity(), bdev_resize_partition(), and
add_partition(). The first has a size check. I don't immediately see a
size check in the other two. Maybe it's there and I need to look
closer. Also can the size of a block device be set in other ways?
Then I have to remember whether a multiplication of a signed value gets
reliably optimized to a shift on all architectures or not. I think so.
Anyway, the trivial version avoids having to consider any of this...
- Eric
next prev parent reply other threads:[~2025-11-04 18:11 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20251030072956.454679-1-yangyongpeng.storage@gmail.com>
2025-11-03 16:48 ` [PATCH v2] fscrypt: fix left shift underflow when inode->i_blkbits > PAGE_SHIFT Eric Biggers
2025-11-04 11:12 ` Christoph Hellwig
2025-11-04 15:05 ` Yongpeng Yang
2025-11-05 13:38 ` Christoph Hellwig
2025-11-04 18:10 ` Eric Biggers [this message]
2025-11-05 13:40 ` Christoph Hellwig
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