From: Prasad J Pandit 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 for 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. Reported-by: Li Qiang Signed-off-by: Prasad J Pandit --- hw/scsi/vmw_pvscsi.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) Update as per: -> https://lists.gnu.org/archive/html/qemu-devel/2016-09/msg01172.html diff --git a/hw/scsi/vmw_pvscsi.c b/hw/scsi/vmw_pvscsi.c index 4245c15..babac5a 100644 --- a/hw/scsi/vmw_pvscsi.c +++ b/hw/scsi/vmw_pvscsi.c @@ -40,6 +40,8 @@ #define PVSCSI_MAX_DEVS (64) #define PVSCSI_MSIX_NUM_VECTORS (1) +#define PVSCSI_MAX_SG_ELEM 2048 + #define PVSCSI_MAX_CMD_DATA_WORDS \ (sizeof(PVSCSICmdDescSetupRings)/sizeof(uint32_t)) @@ -628,17 +630,16 @@ pvscsi_queue_pending_descriptor(PVSCSIState *s, SCSIDevice **d, static void pvscsi_convert_sglist(PVSCSIRequest *r) { - int chunk_size; + uint32_t chunk_size, elmcnt = 0; uint64_t data_length = r->req.dataLen; PVSCSISGState sg = r->sg; - while (data_length) { - while (!sg.resid) { + while (data_length && elmcnt < PVSCSI_MAX_SG_ELEM) { + while (!sg.resid && elmcnt++ < PVSCSI_MAX_SG_ELEM) { pvscsi_get_next_sg_elem(&sg); trace_pvscsi_convert_sglist(r->req.context, r->sg.dataAddr, r->sg.resid); } - assert(data_length > 0); - chunk_size = MIN((unsigned) data_length, sg.resid); + chunk_size = MIN(data_length, sg.resid); if (chunk_size) { qemu_sglist_add(&r->sgl, sg.dataAddr, chunk_size); } -- 2.5.5