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

Eric Sandeen
2015-03-10T13:27:07Z

On 3/9/15 9:17 PM, Brian Foster wrote:
> 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.

Hum, yes, I guess so ("namelen == 0" kind of threw me off).

I'll see how to handle that w/o more cut & paste.