Re: [PATCH V2] xfsdump: prevent segfault in cb_add_inogrp

[Dave Chinner <david@fromorbit.com>]

On Wed, Aug 26, 2015 at 04:57:37PM -0500, Rich Johnston wrote:
> Dave,
> 
> On 08/26/2015 04:37 PM, Dave Chinner wrote:
> >On Wed, Aug 26, 2015 at 12:36:42PM -0500, rjohnston@sgi.com wrote:
> >>The call to memset will segfault because the offset for the first
> >>parameter is done twice. We are using pointer math to do the
> >>calculation.
> >>The first time is when calculating oldsize, the size of i2gseg_t
> >>is accounted for.
> >>	oldsize = (numsegs - SEGPERHNK) * sizeof(i2gseg_t);
> >>Then in the call to memset, oldsize is again multiplied by the size
> >>of i2gmap_t.
> >>	memset(inomap.i2gmap + oldsize, ...)
> >>	
> >>i2gmap holds the used inodes in each chunk. When there are 2^31 chunk
> >>entries, it could describe 2^31 (1 inode/chunk)- 2^40 (64 inodes/chunk).
> >>
> >>With 100s of millions of inodes there are enough entries to wrap the
> >>32 bit variable oldsize.
> >>
> >>Switching to use array index notation instead of calculating the
> >>pointer address twice ;) would resolve this issue. The unneeded
> >>local variable oldsize can be removed as well.
> >>
> Per your other comment I will add a bounds check after calculating numsegs:
> 	if (numsegs < 0)
> 		return -1;
> 
> The description above will change to:
> 
> Adding a bounds check (numsegs < 0) and switching to use array
> index notation instead of calculating the pointer address twice ;)
> would resolve this issue. The unneeded local variable oldsize
> can be removed as well.

Sounds good. Thanks, Rich.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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