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

[Brian Foster <bfoster@redhat.com>]

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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