Re: [PATCH] xfs_repair: junk last entry in sf dir if name starts beyond dir size

Brian Foster
2015-03-10T01:17:55Z

On Mon, Mar 09, 2015 at 04:13:16PM -0400, Eric Sandeen wrote:
> When process_sf_dir2() is trying to salvage entries in a corrupted
> short form directory, it may attempt to shorten the last entry in
> the dir if it extends beyond the directory size.
>
> However, if the name already starts past the dir size, no amount
> of name-shortening will make it fit, but the code doesn't realize
> this. The namelen variable comes out to be negative, and things
> go downhill from there, resulting in a segfault when we try to
> memmove a negative number of bytes.
>
> If no amount of name-shortening can make the last dir entry fit
> in the dir size, simply junk the entry.
>
> Reported by: Rui Gomes <rgomes@rvx.is>
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
>
> This adds a bit more spaghetti to an existing pot, but I think
> it clearly fixes the problem; I might try to rework these cases
> to coalesce some of the code.
>
> (I also wonder about the tradeoff between shortening entries and
> increasing the dir size, but for now I'm just following the
> direction the repair code already takes).
>

Seems Ok on a first glance. The fix is associated with the specific
namelen calculation. Are we susceptible to a similar problem in the
previous branch where we also calculate namelen from the dir size (the
namelen == 0 case)? It looks like we could set a bad value there.

Brian

> diff --git a/repair/dir2.c b/repair/dir2.c
> index 6b8964d..308808d 100644
> --- a/repair/dir2.c
> +++ b/repair/dir2.c
> @@ -911,6 +911,20 @@ _("zero length entry in shortform dir %" PRIu64 ""),
> namelen = ino_dir_size -
> ((__psint_t) &sfep->name[0] -
> (__psint_t) sfp);
> + /* Entry name starts past size of dir; junk it */
> + if (namelen <= 0) {
> + do_warn(
> +_("start of last entry name overflows space left in in shortform dir %" PRIu64 ", "),
> + ino);
> + if (!no_modify)
> + do_warn(
> + _("junking entry #%d\n"), i);
> + else
> + do_warn(
> + _("would junk entry #%d\n"), i);
> + break;
> + }
> + /* Ok, truncate this entry to end of dir */
> do_warn(
> _("size of last entry overflows space left in in shortform dir %" PRIu64 ", "),
> ino);
>
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