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[v4,for-6.0,08/12] esp: don't overflow cmdfifo in get_cmd()

Message ID 20210407195801.685-9-mark.cave-ayland@ilande.co.uk
State New
Headers show
Series esp: fix asserts/segfaults discovered by fuzzer | expand

Commit Message

Mark Cave-Ayland April 7, 2021, 7:57 p.m. UTC 
If the guest tries to read a CDB using DMA and cmdfifo is not empty then it is
possible to overflow cmdfifo.

Since this can only occur by issuing deliberately incorrect instruction
sequences, ensure that the maximum length of the CDB transferred to cmdfifo is
limited to the available free space within cmdfifo.

Buglink: https://bugs.launchpad.net/qemu/+bug/1909247
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Alexander Bulekov <alxndr@bu.edu>
---
 hw/scsi/esp.c | 2 ++
 1 file changed, 2 insertions(+)
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Patch

diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
index 7f49522e1d..53cc569e8a 100644
--- a/hw/scsi/esp.c
+++ b/hw/scsi/esp.c
@@ -243,6 +243,7 @@  static uint32_t get_cmd(ESPState *s, uint32_t maxlen)
         }
         if (s->dma_memory_read) {
             s->dma_memory_read(s->dma_opaque, buf, dmalen);
+            dmalen = MIN(fifo8_num_free(&s->cmdfifo), dmalen);
             fifo8_push_all(&s->cmdfifo, buf, dmalen);
         } else {
             if (esp_select(s) < 0) {
@@ -262,6 +263,7 @@  static uint32_t get_cmd(ESPState *s, uint32_t maxlen)
         if (n >= 3) {
             buf[0] = buf[2] >> 5;
         }
+        n = MIN(fifo8_num_free(&s->cmdfifo), n);
         fifo8_push_all(&s->cmdfifo, buf, n);
     }
     trace_esp_get_cmd(dmalen, target);