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scsi: pvscsi: limit loop to fetch SG list 

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.

Reported-by: Li Qiang <liqiang6-s@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Message-Id: <1473108643-12983-1-git-send-email-ppandit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Prasad J Pandit 2016-09-06 02:20:43 +05:30 committed by Paolo Bonzini
parent a2feb3483e
commit 49adc5d3f8
1 changed files with 6 additions and 5 deletions
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11
hw/scsi/vmw_pvscsi.c
View File

@ -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);
}