From: Linus Torvalds <torvalds@linux-foundation.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [git pull] work.misc
Date: Sun, 2 May 2021 11:14:54 -0700 [thread overview]
Message-ID: <CAHk-=wi=33579pjCosU6QSEu-=HZo+=mnDdQi7zFLskhi-B-mg@mail.gmail.com> (raw)
In-Reply-To: <20210502175946.GY1847222@casper.infradead.org>
On Sun, May 2, 2021 at 11:00 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> I think we have checks that the hw blocksize is a power-of-two (maybe
> just in SCSI? see sd_read_capacity())
Not the hardware block size: our own fs/buffer.c block size.
I could imagine some fs corruption that causes a filesystem to ask for
something like a 1536-byte block size, and I don't see __bread() for
example checking that 'size' is actually a power of 2.
And if it isn't a power of two, then I see __find_get_block() and
__getblk_slow() doing insane things and possibly even overflowing the
allocated page.
Some filesystems actually start from the blocksize on disk (xfs looks
to do that), and do things like
sb->s_blocksize = mp->m_sb.sb_blocksize;
sb->s_blocksize_bits = ffs(sb->s_blocksize) - 1;
and just imagine what happens if the blocksize on disk is 1536... Now,
xfs has a check in the SB validation routine:
sbp->sb_blocksize != (1 << sbp->sb_blocklog)
and if that fails, it will return -EFSCORRUPTED. But what about other
random filesystems?
Hopefully everybody checks it. But my point is, that passing in "size"
instead of "bits" not only caused this ffs() optimization, it's also a
potential source of subtle problems..
(But it goes back to the dark ages, I'm not blaming anybody but myself).
Linus
next prev parent reply other threads:[~2021-05-02 18:15 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-02 1:30 [git pull] work.misc Al Viro
2021-05-02 16:26 ` Linus Torvalds
2021-05-02 17:59 ` Matthew Wilcox
2021-05-02 18:14 ` Linus Torvalds [this message]
2021-05-02 18:32 ` pr-tracker-bot
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