Re: [Qemu-devel] [PATCH v2] scsi: pvscsi: check request descriptor SG element count

[P J P <ppandit@redhat.com>]

  Hello Paolo,

+-- On Tue, 6 Sep 2016, Paolo Bonzini wrote --+
| The commit message is not correct, because you're fixing the bug in two
| different ways: by removing the cast and by limiting the number of
| iterations in the loop.

  Ah, yes; Sorry about that.

| ---
| In PVSCSI paravirtual SCSI bus, pvscsi_convert_sglist can take a very
| long time or go into an infinite loop due to two different bugs:
| 
| 1) the request descriptor data length is defined to be 64 bit. While
| building SG list from a request descriptor, it gets truncated to 32bit
| in routine 'pvscsi_convert_sglist'. This could lead to an infinite loop
| situation large 'dataLen' values when data_length is cast to uint32_t
| and chunk_size becomes always zero.  Fix this by removing the incorrect
| cast.
| 
| 2) pvscsi_get_next_sg_elem can be called arbitrarily many times if the
| element has a zero length.  Get out of the loop early when this happens,
| by introducing an upper limit on the number of SG list elements.
| ---

  Done; I've sent a revised patch v3 with this commit message.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
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