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

From: Kees Cook
Date: Thu Oct 31 2013 - 15:08:40 EST

On Thu, Oct 31, 2013 at 12:06 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> 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?

Agreed. MAINTAINERS shows it as orphaned. Perhaps it should be moved
into staging?


Kees Cook
Chrome OS Security
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