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esp: don't underflow cmdfifo in do_cmd()

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If the guest tries to execute a CDB when cmdfifo is not empty before the start
of the message out phase then clearing the message out phase data will cause
cmdfifo to underflow due to cmdfifo_cdb_offset being larger than the amount of
data within.

Since this can only occur by issuing deliberately incorrect instruction
sequences, ensure that the maximum length of esp_fifo_pop_buf() is limited to
the size of the data 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>
Message-Id: <20210407195801.685-8-mark.cave-ayland@ilande.co.uk>
This commit is contained in:
Mark Cave-Ayland 2021-04-07 20:57:56 +01:00
parent 9954575173
commit fa7505c154
1 changed files with 4 additions and 2 deletions
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6
hw/scsi/esp.c
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@ -319,13 +319,15 @@ static void do_busid_cmd(ESPState *s, uint8_t busid)
static void do_cmd(ESPState *s)
{
uint8_t busid = fifo8_pop(&s->cmdfifo);
uint8_t busid = esp_fifo_pop(&s->cmdfifo);
int len;
s->cmdfifo_cdb_offset--;
/* Ignore extended messages for now */
if (s->cmdfifo_cdb_offset) {
esp_fifo_pop_buf(&s->cmdfifo, NULL, s->cmdfifo_cdb_offset);
len = MIN(s->cmdfifo_cdb_offset, fifo8_num_used(&s->cmdfifo));
esp_fifo_pop_buf(&s->cmdfifo, NULL, len);
s->cmdfifo_cdb_offset = 0;
}