[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH 3/3] scsi: megasas: check 'read_queue_head' inde

From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH 3/3] scsi: megasas: check 'read_queue_head' index value
Date: Wed, 25 May 2016 13:20:53 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

On 05/25/2016 12:31 PM, P J P wrote:
From: Prasad J Pandit <address@hidden>

While doing MegaRAID SAS controller command frame lookup, routine
'megasas_lookup_frame' uses 'read_queue_head' value as an index
into 'frames[MEGASAS_MAX_FRAMES=2048]' array. Limit its value
within array bounds to avoid any OOB access.

Reported-by: Li Qiang <address@hidden>
Signed-off-by: Prasad J Pandit <address@hidden>
  hw/scsi/megasas.c | 6 ++++--
  1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c
index 7c08932..76d57f9 100644
--- a/hw/scsi/megasas.c
+++ b/hw/scsi/megasas.c
@@ -649,8 +649,10 @@ static int megasas_init_firmware(MegasasState *s, 
MegasasCmd *cmd)
      pa_lo = le32_to_cpu(initq->pi_addr_lo);
      pa_hi = le32_to_cpu(initq->pi_addr_hi);
      s->producer_pa = ((uint64_t) pa_hi << 32) | pa_lo;
-    s->reply_queue_head = ldl_le_pci_dma(pcid, s->producer_pa);
-    s->reply_queue_tail = ldl_le_pci_dma(pcid, s->consumer_pa);
+    s->reply_queue_head = \
+        ldl_le_pci_dma(pcid, s->producer_pa) % MEGASAS_MAX_FRAMES;
+    s->reply_queue_tail = \
+        ldl_le_pci_dma(pcid, s->consumer_pa) % MEGASAS_MAX_FRAMES;

You're using up 2 lines for each of those assignments now anyway, so why not just split it into

  s->reply_queue_head = ldl_le_pci_dma(pcid, s->producer_pa);
  s->reply_queue_head %= MEGASAS_MAX_FRAMES;

and that way avoid a real multi-line statement (which is hard to read).

Whether the bitmask really is what hardware would do, I don't know. I'll let Hannes comment there. Maybe the hardware simply does

s->reply_queue_head = MIN(ldl_le_pci_dma(pcid, s->producer_pa), MEGASAS_MAX_FRAMES);

But I agree that the mask is more likely.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]