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SubjectRe: [PATCH] NFS: Check lengths more thoroughly in NFS4 readdir XDR decode
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On Thu, 2006-08-24 at 19:35 +0100, David Howells wrote:
> So, what you've done is:
>
> -+ if (end - p < xlen)
> ++ if (end - p < xlen + 1)
> goto short_pkt;
> + dprintk("filename = %*s\n", len, (char *)p);
> + p += xlen;
> len = ntohl(*p++); /* bitmap length */
> - p += len;
> - if (p + 1 > end)
> -+ if (end - p < len)
> ++ if (end - p < len + 1)
> goto short_pkt;
> + p += len;
> attrlen = XDR_QUADLEN(ntohl(*p++));
> - p += attrlen; /* attributes */
> - if (p + 2 > end)
> -+ if (end - p < attrlen + 1)
> ++ if (end - p < attrlen + 2)
>
> But is this equivalent:
>
> -+ if (end - p < xlen)
> ++ if (end - p <= xlen)
> goto short_pkt;
> + dprintk("filename = %*s\n", len, (char *)p);
> + p += xlen;
> len = ntohl(*p++); /* bitmap length */
> - p += len;
> - if (p + 1 > end)
> -+ if (end - p < len)
> ++ if (end - p <= len)
> goto short_pkt;
> + p += len;
> attrlen = XDR_QUADLEN(ntohl(*p++));
> - p += attrlen; /* attributes */
> - if (p + 2 > end)
> -+ if (end - p < attrlen + 1)
> ++ if (end - p <= attrlen + 1)
^^^^^^^^^^^^^^

> Do you think?

No. I find that mixture of < and <= is much less easy to read. Besides,
the compiler should be able to optimise that for me.

Cheers,
Trond

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