Commit message: block/iscsi:fix heap-buffer-overflow in iscsi_aio_ioctl_cb

There is an overflow, the source 'datain.data[2]' is 100 bytes,
 but the 'ss' is 252 bytes.This may cause a security issue because
 we can access a lot of unrelated memory data.

The len for sbp copy data should take the minimum of mx_sb_len and
 sb_len_wr, not the maximum.

If we use iscsi device for VM backend storage, ASAN show stack:

READ of size 252 at 0xfffd149dcfc4 thread T0
    #0 0xaaad433d0d34 in __asan_memcpy (aarch64-softmmu/qemu-system-aarch64+0x2cb0d34)
    #1 0xaaad45f9d6d0 in iscsi_aio_ioctl_cb /qemu/block/iscsi.c:996:9
    #2 0xfffd1af0e2dc  (/usr/lib64/iscsi/libiscsi.so.8+0xe2dc)
    #3 0xfffd1af0d174  (/usr/lib64/iscsi/libiscsi.so.8+0xd174)
    #4 0xfffd1af19fac  (/usr/lib64/iscsi/libiscsi.so.8+0x19fac)
    #5 0xaaad45f9acc8 in iscsi_process_read /qemu/block/iscsi.c:403:5
    #6 0xaaad4623733c in aio_dispatch_handler /qemu/util/aio-posix.c:467:9
    #7 0xaaad4622f350 in aio_dispatch_handlers /qemu/util/aio-posix.c:510:20
    #8 0xaaad4622f350 in aio_dispatch /qemu/util/aio-posix.c:520
    #9 0xaaad46215944 in aio_ctx_dispatch /qemu/util/async.c:298:5
    #10 0xfffd1bed12f4 in g_main_context_dispatch (/lib64/libglib-2.0.so.0+0x512f4)
    #11 0xaaad46227de0 in glib_pollfds_poll /qemu/util/main-loop.c:219:9
    #12 0xaaad46227de0 in os_host_main_loop_wait /qemu/util/main-loop.c:242
    #13 0xaaad46227de0 in main_loop_wait /qemu/util/main-loop.c:518
    #14 0xaaad43d9d60c in qemu_main_loop /qemu/softmmu/vl.c:1662:9
    #15 0xaaad4607a5b0 in main /qemu/softmmu/main.c:49:5
    #16 0xfffd1a460b9c in __libc_start_main (/lib64/libc.so.6+0x20b9c)
    #17 0xaaad43320740 in _start (aarch64-softmmu/qemu-system-aarch64+0x2c00740)

0xfffd149dcfc4 is located 0 bytes to the right of 100-byte region [0xfffd149dcf60,0xfffd149dcfc4)
allocated by thread T0 here:
    #0 0xaaad433d1e70 in __interceptor_malloc (aarch64-softmmu/qemu-system-aarch64+0x2cb1e70)
    #1 0xfffd1af0e254  (/usr/lib64/iscsi/libiscsi.so.8+0xe254)
    #2 0xfffd1af0d174  (/usr/lib64/iscsi/libiscsi.so.8+0xd174)
    #3 0xfffd1af19fac  (/usr/lib64/iscsi/libiscsi.so.8+0x19fac)
    #4 0xaaad45f9acc8 in iscsi_process_read /qemu/block/iscsi.c:403:5
    #5 0xaaad4623733c in aio_dispatch_handler /qemu/util/aio-posix.c:467:9
    #6 0xaaad4622f350 in aio_dispatch_handlers /qemu/util/aio-posix.c:510:20
    #7 0xaaad4622f350 in aio_dispatch /qemu/util/aio-posix.c:520
    #8 0xaaad46215944 in aio_ctx_dispatch /qemu/util/async.c:298:5
    #9 0xfffd1bed12f4 in g_main_context_dispatch (/lib64/libglib-2.0.so.0+0x512f4)
    #10 0xaaad46227de0 in glib_pollfds_poll /qemu/util/main-loop.c:219:9
    #11 0xaaad46227de0 in os_host_main_loop_wait /qemu/util/main-loop.c:242
    #12 0xaaad46227de0 in main_loop_wait /qemu/util/main-loop.c:518
    #13 0xaaad43d9d60c in qemu_main_loop /qemu/softmmu/vl.c:1662:9
    #14 0xaaad4607a5b0 in main /qemu/softmmu/main.c:49:5
    #15 0xfffd1a460b9c in __libc_start_main (/lib64/libc.so.6+0x20b9c)
    #16 0xaaad43320740 in _start (aarch64-softmmu/qemu-system-aarch64+0x2c00740)

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Chen Qun <kuhn.chenqun@huawei.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20200418062602.10776-1-kuhn.chenqun@huawei.com
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
CVE: CVE-2020-11947
CWE: CWE-125
Vulnerability description: iscsi_aio_ioctl_cb in block/iscsi.c in QEMU 4.1.0 has a heap-based buffer over-read that may disclose unrelated information from process memory to an attacker.

Project: qemu
File: iscsi.c

iscsi_aio_ioctl_cb(struct iscsi_context *iscsi, int status,
                     void *command_data, void *opaque)
{
    IscsiAIOCB *acb = opaque;

    if (status == SCSI_STATUS_CANCELLED) {
        if (!acb->bh) {
            acb->status = -ECANCELED;
            iscsi_schedule_bh(acb);
        }
        return;
    }

    acb->status = 0;
    if (status < 0) {
        error_report("Failed to ioctl(SG_IO) to iSCSI lun. %s",
                     iscsi_get_error(iscsi));
        acb->status = -iscsi_translate_sense(&acb->task->sense);
    }

    acb->ioh->driver_status = 0;
    acb->ioh->host_status   = 0;
    acb->ioh->resid         = 0;
    acb->ioh->status        = status;

#define SG_ERR_DRIVER_SENSE    0x08

    if (status == SCSI_STATUS_CHECK_CONDITION && acb->task->datain.size >= 2) {
        int ss;

        acb->ioh->driver_status |= SG_ERR_DRIVER_SENSE;

        acb->ioh->sb_len_wr = acb->task->datain.size - 2;
        ss = (acb->ioh->mx_sb_len >= acb->ioh->sb_len_wr) ?
             acb->ioh->mx_sb_len : acb->ioh->sb_len_wr;
        memcpy(acb->ioh->sbp, &acb->task->datain.data[2], ss);
    }

    iscsi_schedule_bh(acb);
}