Commit de594e47 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

scsi: lsi: exit infinite loop while executing script (CVE-2019-12068) 



When executing script in lsi_execute_script(), the LSI scsi adapter
emulator advances 's->dsp' index to read next opcode. This can lead
to an infinite loop if the next opcode is empty. Move the existing
loop exit after 10k iterations so that it covers no-op opcodes as
well.

Reported-by: default avatarBugs SysSec <bugs-syssec@rub.de>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarPrasad J Pandit <pjp@fedoraproject.org>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent a0602978

hw/scsi/lsi53c895a.c

+27 −14
Original line number Diff line number Diff line
@@ -186,6 +186,9 @@ static const char *names[] = { 
/* Flag set if this is a tagged command.  */

#define LSI_TAG_VALID     (1 << 16)



/* Maximum instructions to process. */

#define LSI_MAX_INSN    10000



typedef struct lsi_request {

    SCSIRequest *req;

    uint32_t tag;
@@ -1133,7 +1136,21 @@ static void lsi_execute_script(LSIState *s) 


    s->istat1 |= LSI_ISTAT1_SRUN;

again:

    insn_processed++;

    if (++insn_processed > LSI_MAX_INSN) {

        /* Some windows drivers make the device spin waiting for a memory

           location to change.  If we have been executed a lot of code then

           assume this is the case and force an unexpected device disconnect.

           This is apparently sufficient to beat the drivers into submission.

         */

        if (!(s->sien0 & LSI_SIST0_UDC)) {

            qemu_log_mask(LOG_GUEST_ERROR,

                          "lsi_scsi: inf. loop with UDC masked");

        }

        lsi_script_scsi_interrupt(s, LSI_SIST0_UDC, 0);

        lsi_disconnect(s);

        trace_lsi_execute_script_stop();

        return;

    }

    insn = read_dword(s, s->dsp);

    if (!insn) {

        /* If we receive an empty opcode increment the DSP by 4 bytes
@@ -1570,19 +1587,7 @@ again: 
            }

        }

    }

    if (insn_processed > 10000 && s->waiting == LSI_NOWAIT) {

        /* Some windows drivers make the device spin waiting for a memory

           location to change.  If we have been executed a lot of code then

           assume this is the case and force an unexpected device disconnect.

           This is apparently sufficient to beat the drivers into submission.

         */

        if (!(s->sien0 & LSI_SIST0_UDC)) {

            qemu_log_mask(LOG_GUEST_ERROR,

                          "lsi_scsi: inf. loop with UDC masked");

        }

        lsi_script_scsi_interrupt(s, LSI_SIST0_UDC, 0);

        lsi_disconnect(s);

    } else if (s->istat1 & LSI_ISTAT1_SRUN && s->waiting == LSI_NOWAIT) {

    if (s->istat1 & LSI_ISTAT1_SRUN && s->waiting == LSI_NOWAIT) {

        if (s->dcntl & LSI_DCNTL_SSM) {

            lsi_script_dma_interrupt(s, LSI_DSTAT_SSI);

        } else {
@@ -1970,6 +1975,10 @@ static void lsi_reg_writeb(LSIState *s, int offset, uint8_t val) 
    case 0x2f: /* DSP[24:31] */

        s->dsp &= 0x00ffffff;

        s->dsp |= val << 24;

        /*

         * FIXME: if s->waiting != LSI_NOWAIT, this will only execute one

         * instruction.  Is this correct?

         */

        if ((s->dmode & LSI_DMODE_MAN) == 0

            && (s->istat1 & LSI_ISTAT1_SRUN) == 0)

            lsi_execute_script(s);
@@ -1988,6 +1997,10 @@ static void lsi_reg_writeb(LSIState *s, int offset, uint8_t val) 
        break;

    case 0x3b: /* DCNTL */

        s->dcntl = val & ~(LSI_DCNTL_PFF | LSI_DCNTL_STD);

        /*

         * FIXME: if s->waiting != LSI_NOWAIT, this will only execute one

         * instruction.  Is this correct?

         */

        if ((val & LSI_DCNTL_STD) && (s->istat1 & LSI_ISTAT1_SRUN) == 0)

            lsi_execute_script(s);

        break;