Re: [PATCH] xfsdump: prevent segfault in cb_add_inogrp

[Eric Sandeen <sandeen@sandeen.net>]

On 8/26/15 9:33 AM, 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.

Ok, this doesn't explain the type change for numsegs, does it?

Can you walk me through why that's needed?  At what point would
numsegs = inomap.hnkmaplen * SEGPERHNK; overflow?

Thanks,
-Eric

> ---
>  dump/inomap.c |    8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> Index: b/dump/inomap.c
> ===================================================================
> --- a/dump/inomap.c
> +++ b/dump/inomap.c
> @@ -1125,8 +1125,7 @@ cb_add_inogrp( void *arg1, intgen_t fsfd
>  		lastsegp->segoff = 0;
>  
>  		if (lastsegp->hnkoff == inomap.hnkmaplen) {
> -			intgen_t numsegs;
> -			intgen_t oldsize;
> +			int64_t numsegs;
>  
>  			inomap.hnkmaplen++;
>  			inomap.hnkmap = (hnk_t *)
> @@ -1140,10 +1139,7 @@ cb_add_inogrp( void *arg1, intgen_t fsfd
>  				return -1;
>  
>  			/* zero the new portion of the i2gmap */
> -			oldsize = (numsegs - SEGPERHNK) * sizeof(i2gseg_t);
> -
> -			memset(inomap.i2gmap + oldsize,
> -			       0,
> +			memset(&inomap.i2gmap[numsegs - SEGPERHNK], 0,
>  			       SEGPERHNK * sizeof(i2gseg_t));
>  		}
>  
> 
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> 

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