linux-kernel - Re: FAT: Operating on broken FAT FS causes the write syscall to return negative number not equal to -1

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Date:   Sun, 15 Jul 2018 18:35:40 +0300
From:   Anatoly Trosinenko <anatoly.trosinenko@...il.com>
To:     OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:     viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: FAT: Operating on broken FAT FS causes the write syscall to
 return negative number not equal to -1

Thanks for explanation!

Best regards,
Anatoly

вс, 15 июл. 2018 г. в 18:26, OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>:
>
> Anatoly Trosinenko <anatoly.trosinenko@...il.com> writes:
>
> >> This patch returns better error (-EIO) for me.
> >
> > This works for me likewise.
>
> Thanks for testing.
>
> >> (But note, the corrupted FS image doesn't guarantee POSIX behavior.)
> >
> > Oops, I was just doing some testing and thought that correct behavior
> > for crafted FS is to return arbitrary valid error code (like -EIO) or
> > some arbitrary data, say, not larger than FS (not disclosing the
> > kernel memory, of course). Please excuse me if I was wrong. If fixing
> > this would slow down some hot code path, then I am not insisting on
> > returning valid errno. :)
> >
> > Meanwhile, how should be considered such discrepancies with man pages
> > for invalid FS images: should it be considered low priority bug,
> > not-a-bug or feature request (diagnostics)?
>
> To handle the corrupted image _perfectly_, finally we will have to have
> online fsck or similar.
>
> For example, if the data block was shared between the regular file and
> directory, user can mmap the directory data via (corrupted) regular
> file.
>
> Then locking of directory handler doesn't work, and handler has to have
> directory data as volatile data (and validate data for each memory
> load). And to verify this invalid shared data blocks, we will have to
> read all inodes (i.e. almost fsck).
>
> So, I may change the code if data verification is easy and lightweight
> like in this case. But like said above, it will not be guaranteed.
>
> Thanks.
> --
> OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>