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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Message-ID: <CAE5jQCcs2x4myTHUhNmHPZvhMuPsrkzLmiqqeF5wzZ-Hf5druQ@mail.gmail.com>
Date:   Sun, 15 Jul 2018 18:08:23 +0300
From:   Anatoly Trosinenko <anatoly.trosinenko@...il.com>
To:     viro@...iv.linux.org.uk
Cc:     OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        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

Thank you!

> This patch returns better error (-EIO) for me.

This works for me likewise.

> (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)?

Thanks
Anatoly

вс, 15 июл. 2018 г. в 17:30, Al Viro <viro@...iv.linux.org.uk>:
>
> On Sun, Jul 15, 2018 at 11:20:06PM +0900, OGAWA Hirofumi wrote:
> > +static inline bool fat_valid_entry(struct msdos_sb_info *sbi, int entry)
> > +{
> > +     if (entry < FAT_START_ENT || sbi->max_cluster <= entry)
> > +             return false;
> > +     return true;
> > +}
>
> Pet peeve: if (...) return false; return true; instead of return !....;
>
> In this case,
>         return entry >= FAT_START_ENT && entry < sb->max_cluster;