Re: [Qemu-devel] [PATCH 2/2] hw: fw_cfg: refactor fw_cfg_reboot()

[李强]

At 2018-11-17 00:52:58, "Markus Armbruster" <address@hidden> wrote:
>Li Qiang <address@hidden> writes:
>
>> Currently the user can set a negative reboot_timeout.
>> Also it is wrong to parse 'reboot-timeout' with qemu_opt_get() and then
>> convert it to number.
>
>Again, it's not wrong per se, just needlessly complicated and
>error-prone.  What makes it wrong is ...
>
>> convert it to number. This patch refactor this function by following:
>> 1. ensure reboot_timeout is in 0~0xffff
>> 2. use qemu_opt_get_number() to parse reboot_timeout
>> 3. simlify code
>>
>> Signed-off-by: Li Qiang <address@hidden>
>> ---
>>  hw/nvram/fw_cfg.c | 23 +++++++++++------------
>>  vl.c              |  2 +-
>>  2 files changed, 12 insertions(+), 13 deletions(-)
>>
>> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
>> index 78f43dad93..6aca80846a 100644
>> --- a/hw/nvram/fw_cfg.c
>> +++ b/hw/nvram/fw_cfg.c
>> @@ -178,24 +178,23 @@ static void fw_cfg_bootsplash(FWCfgState *s)
>>  
>>  static void fw_cfg_reboot(FWCfgState *s)
>>  {
>> -    int reboot_timeout = -1;
>> -    char *p;
>> -    const char *temp;
>> +    const char *reboot_timeout = NULL;
>>  
>>      /* get user configuration */
>>      QemuOptsList *plist = qemu_find_opts("boot-opts");
>>      QemuOpts *opts = QTAILQ_FIRST(&plist->head);
>> -    if (opts != NULL) {
>> -        temp = qemu_opt_get(opts, "reboot-timeout");
>> -        if (temp != NULL) {
>> -            p = (char *)temp;
>> -            reboot_timeout = strtol(p, &p, 10);
>
>... the total lack of error checking here.  Same in PATCH 1.

>


Got.


>Here's my attempt at a clearer commit message:
>
>    fw_cfg: Fix -boot reboot-timeout error checking
>
>    fw_cfg_reboot() gets option parameter "reboot-timeout" with
>    qemu_opt_get(), then converts it to an integer by hand.  It neglects
>    to check that conversion for errors, and fails to reject negative
>    values.  Positive values above the limit get reported and replaced
>    by the limit.
>
>    Check for conversion errors properly, and reject all values outside
>    0..0xffff.

>


Thanks for your advice, I appreciate it and will change in the revision version.


>PATCH 1's commit message could be improved the same way.
>
>> -        }
>> +    reboot_timeout = qemu_opt_get(opts, "reboot-timeout");
>> +
>> +    if (reboot_timeout == NULL) {
>> +        return;
>>      }
>> +    int64_t rt_val = qemu_opt_get_number(opts, "reboot-timeout", -1);
>> +
>>      /* validate the input */
>> -    if (reboot_timeout > 0xffff) {
>> -        error_report("reboot timeout is larger than 65535, force it to 
>> 65535.");
>> -        reboot_timeout = 0xffff;
>> +    if (rt_val < 0 || rt_val > 0xffff) {
>> +        error_report("reboot timeout is invalid,"
>> +                     "it should be a value between 0 and 65535");
>> +        exit(1);
>>      }
>>      fw_cfg_add_file(s, "etc/boot-fail-wait", g_memdup(&reboot_timeout, 4), 
>> 4);
>>  }
>
>Change in behavior when "reboot-timeout" isn't specified.
>
>Before your patch, we fw_cfg_add_file() with a value of -1.
>
>After your patch, we don't fw_cfg_add_file().
>
>Why is that okay?

>


Here I following Gerd's advice. 
For values >0xffff  or < 0, report and exit.
-->http://lists.gnu.org/archive/html/qemu-devel/2018-11/msg00551.html
Thanks,
Li Qiang
>> diff --git a/vl.c b/vl.c
>> index be37da46f0..086127ff0b 100644
>> --- a/vl.c
>> +++ b/vl.c
>> @@ -339,7 +339,7 @@ static QemuOptsList qemu_boot_opts = {
>>              .type = QEMU_OPT_NUMBER,
>>          }, {
>>              .name = "reboot-timeout",
>> -            .type = QEMU_OPT_STRING,
>> +            .type = QEMU_OPT_NUMBER,
>>          }, {
>>              .name = "strict",
>>              .type = QEMU_OPT_BOOL,