linux-kernel - Re: [PATCH] fs/befs/linuxvfs.c: need signed cast for variable 'block'

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Date:	Thu, 31 Oct 2013 19:06:08 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Kees Cook <keescook@...omium.org>
Cc:	Chen Gang <gang.chen@...anux.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs/befs/linuxvfs.c: need signed cast for variable 'block'

On Thu, Oct 31, 2013 at 09:53:59AM -0700, Kees Cook wrote:

> If block (type sector_t) is unsigned, we shouldn't cast it signed.
> This entire code path should be removed. What is BEFS's expected
> maximum block size? (Looks like even befs_blocknr_t is u64, so nothing
> seems trivially in danger of wrapping.) I would also note that all the
> format strings are wrong too (%ld instead of %lu).

FWIW, this
        res = befs_fblock2brun(sb, ds, block, &run);
        if (res != BEFS_OK) {
                befs_error(sb,
                           "<--- befs_get_block() for inode %lu, block "
                           "%ld ERROR", inode->i_ino, block);
                return -EFBIG;
        }
also looks wrong - ioctl(..., FIBMAP, ...) shouldn't be able to spew
printks on a valid fs and hitting it with block number greater than
file length will, AFAICS, trigger that.

I agree that this code needs fixing, but just making gcc STFU about the
comparison would only serve to hide the problem.  Anybody familiar with
befs or willing to learn it?
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