Re: [PATCHv2 4/4] scsi_devinfo: fixup string compare
On 08/09/2017 07:43 PM, Alan Stern wrote:
> On Wed, 9 Aug 2017, Hannes Reinecke wrote:
>
>> When checking the model and vendor string we need to use the
>> minimum value of either string, otherwise we'll miss out on
>> wildcard matches.
>
> This is now true only for the model string, not the vendor string. And
> even for the model string, you allow the lengths to differ in only one
> direction (the model string can be longer than the devinfo model
> string, but not vice versa).
>
>> And we should take card when matching with zero size strings;
>> results might be unpredictable.
>> With this patch the rules for matching devinfo strings are
>> as follows:
>> - Vendor strings must match exactly
>> - Empty Model strings will only match if the devinfo model
>> is also empty
>> - Model strings shorter than the devinfo model string will
>> not match
>
> Good, this is a lot better than before. These rules make sense.
>
> However, the rules and the code are both somewhat redundant. For
> example, the second rule above is already a consequence of the third
> rule: If the model string is empty and the devinfo model string isn't,
> then the model string is shorter than the devinfo model string so they
> won't match.
>
>> Fixes: 5e7ff2c ("SCSI: fix new bug in scsi_dev_info_list string matching")
>> Signed-off-by: Hannes Reinecke
>> ---
>> drivers/scsi/scsi_devinfo.c | 46
>> -
>> 1 file changed, 33 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/scsi/scsi_devinfo.c b/drivers/scsi/scsi_devinfo.c
>> index 776c701..f8f5cb7 100644
>> --- a/drivers/scsi/scsi_devinfo.c
>> +++ b/drivers/scsi/scsi_devinfo.c
>> @@ -399,8 +399,8 @@ int scsi_dev_info_list_add_keyed(int compatible, char
>> *vendor, char *model,
>>
>> /**
>> * scsi_dev_info_list_find - find a matching dev_info list entry.
>> - * @vendor: vendor string
>> - * @model: model (product) string
>> + * @vendor: full vendor string
>> + * @model: full model (product) string
>> * @key:specify list to use
>> *
>> * Description:
>> @@ -440,6 +440,8 @@ static struct scsi_dev_info_list
>> *scsi_dev_info_list_find(const char *vendor,
>> /* Also skip trailing spaces */
>> while (vmax > 0 && vskip[vmax - 1] == ' ')
>> --vmax;
>> +if (!vmax)
>> +vskip = NULL;
>>
>> mmax = sizeof(devinfo->model);
>> mskip = model;
>> @@ -449,27 +451,45 @@ static struct scsi_dev_info_list
>> *scsi_dev_info_list_find(const char *vendor,
>> }
>> while (mmax > 0 && mskip[mmax - 1] == ' ')
>> --mmax;
>> +if (!mmax)
>> +mskip = NULL;
>
> Neither of these changes is needed.
>
>>
>> list_for_each_entry(devinfo, _table->scsi_dev_info_list,
>> dev_info_list) {
>> if (devinfo->compatible) {
>> /*
>> - * Behave like the older version of get_device_flags.
>> + * vendor strings must be an exact match
>> */
>> -if (memcmp(devinfo->vendor, vskip, vmax) ||
>> -(vmax < sizeof(devinfo->vendor) &&
>> -devinfo->vendor[vmax]))
>> +if (vmax != strlen(devinfo->vendor))
>> continue;
>> -if (memcmp(devinfo->model, mskip, mmax) ||
>> -(mmax < sizeof(devinfo->model) &&
>> -devinfo->model[mmax]))
>> +if (vskip && vmax &&
>> +memcmp(devinfo->vendor, vskip, vmax))
>> continue;
>
> There's no need to test vskip and vmax. The memcmp test alone is
> sufficient, since you know the lengths are equal and you are looking
> for an exact match. So in the end, you could just do this:
>
> if (vmax != strlen(devinfo->vendor) ||
> memcmp(devinfo->vendor, vskip, vmax))
> continue;
>
Hmm. Let's see; I'll have the testsuite retest this.
>> -return devinfo;
>> +/*
>> + * Empty model strings only match if both strings
>> + * are empty.
>> + */
>> +if (!mmax && !strlen(devinfo->model))
>> +return devinfo;
>
> As mentioned above, this is not necessary.
>
>> +
>> +/*
>> + * Empty @model never matches
>> + */
>> +if (!mskip)
>> +continue;
>
> Nor is this.
>
>> +
>> +/*
>> + * @model specifies the full string, and
>> + * must be larger or equal to devinfo->model
>> + */
>> +
Re: [PATCHv2 4/4] scsi_devinfo: fixup string compare
On Wed, 9 Aug 2017, Hannes Reinecke wrote:
> When checking the model and vendor string we need to use the
> minimum value of either string, otherwise we'll miss out on
> wildcard matches.
This is now true only for the model string, not the vendor string. And
even for the model string, you allow the lengths to differ in only one
direction (the model string can be longer than the devinfo model
string, but not vice versa).
> And we should take card when matching with zero size strings;
> results might be unpredictable.
> With this patch the rules for matching devinfo strings are
> as follows:
> - Vendor strings must match exactly
> - Empty Model strings will only match if the devinfo model
> is also empty
> - Model strings shorter than the devinfo model string will
> not match
Good, this is a lot better than before. These rules make sense.
However, the rules and the code are both somewhat redundant. For
example, the second rule above is already a consequence of the third
rule: If the model string is empty and the devinfo model string isn't,
then the model string is shorter than the devinfo model string so they
won't match.
> Fixes: 5e7ff2c ("SCSI: fix new bug in scsi_dev_info_list string matching")
> Signed-off-by: Hannes Reinecke
> ---
> drivers/scsi/scsi_devinfo.c | 46
> -
> 1 file changed, 33 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/scsi/scsi_devinfo.c b/drivers/scsi/scsi_devinfo.c
> index 776c701..f8f5cb7 100644
> --- a/drivers/scsi/scsi_devinfo.c
> +++ b/drivers/scsi/scsi_devinfo.c
> @@ -399,8 +399,8 @@ int scsi_dev_info_list_add_keyed(int compatible, char
> *vendor, char *model,
>
> /**
> * scsi_dev_info_list_find - find a matching dev_info list entry.
> - * @vendor: vendor string
> - * @model: model (product) string
> + * @vendor: full vendor string
> + * @model: full model (product) string
> * @key: specify list to use
> *
> * Description:
> @@ -440,6 +440,8 @@ static struct scsi_dev_info_list
> *scsi_dev_info_list_find(const char *vendor,
> /* Also skip trailing spaces */
> while (vmax > 0 && vskip[vmax - 1] == ' ')
> --vmax;
> + if (!vmax)
> + vskip = NULL;
>
> mmax = sizeof(devinfo->model);
> mskip = model;
> @@ -449,27 +451,45 @@ static struct scsi_dev_info_list
> *scsi_dev_info_list_find(const char *vendor,
> }
> while (mmax > 0 && mskip[mmax - 1] == ' ')
> --mmax;
> + if (!mmax)
> + mskip = NULL;
Neither of these changes is needed.
>
> list_for_each_entry(devinfo, _table->scsi_dev_info_list,
> dev_info_list) {
> if (devinfo->compatible) {
> /*
> - * Behave like the older version of get_device_flags.
> + * vendor strings must be an exact match
>*/
> - if (memcmp(devinfo->vendor, vskip, vmax) ||
> - (vmax < sizeof(devinfo->vendor) &&
> - devinfo->vendor[vmax]))
> + if (vmax != strlen(devinfo->vendor))
> continue;
> - if (memcmp(devinfo->model, mskip, mmax) ||
> - (mmax < sizeof(devinfo->model) &&
> - devinfo->model[mmax]))
> + if (vskip && vmax &&
> + memcmp(devinfo->vendor, vskip, vmax))
> continue;
There's no need to test vskip and vmax. The memcmp test alone is
sufficient, since you know the lengths are equal and you are looking
for an exact match. So in the end, you could just do this:
if (vmax != strlen(devinfo->vendor) ||
memcmp(devinfo->vendor, vskip, vmax))
continue;
> - return devinfo;
> + /*
> + * Empty model strings only match if both strings
> + * are empty.
> + */
> + if (!mmax && !strlen(devinfo->model))
> + return devinfo;
As mentioned above, this is not necessary.
> +
> + /*
> + * Empty @model never matches
> + */
> + if (!mskip)
> + continue;
Nor is this.
> +
> + /*
> + * @model specifies the full string, and
> + * must be larger or equal to devinfo->model
> + */
> + if (!memcmp(devinfo->model, mskip,
> + strlen(devinfo->model)))
> + return devinfo;
It would be safer to do it this way:
[PATCHv2 4/4] scsi_devinfo: fixup string compare
When checking the model and vendor string we need to use the
minimum value of either string, otherwise we'll miss out on
wildcard matches.
And we should take card when matching with zero size strings;
results might be unpredictable.
With this patch the rules for matching devinfo strings are
as follows:
- Vendor strings must match exactly
- Empty Model strings will only match if the devinfo model
is also empty
- Model strings shorter than the devinfo model string will
not match
Fixes: 5e7ff2c ("SCSI: fix new bug in scsi_dev_info_list string matching")
Signed-off-by: Hannes Reinecke
---
drivers/scsi/scsi_devinfo.c | 46 -
1 file changed, 33 insertions(+), 13 deletions(-)
diff --git a/drivers/scsi/scsi_devinfo.c b/drivers/scsi/scsi_devinfo.c
index 776c701..f8f5cb7 100644
--- a/drivers/scsi/scsi_devinfo.c
+++ b/drivers/scsi/scsi_devinfo.c
@@ -399,8 +399,8 @@ int scsi_dev_info_list_add_keyed(int compatible, char
*vendor, char *model,
/**
* scsi_dev_info_list_find - find a matching dev_info list entry.
- * @vendor:vendor string
- * @model: model (product) string
+ * @vendor:full vendor string
+ * @model: full model (product) string
* @key: specify list to use
*
* Description:
@@ -440,6 +440,8 @@ static struct scsi_dev_info_list
*scsi_dev_info_list_find(const char *vendor,
/* Also skip trailing spaces */
while (vmax > 0 && vskip[vmax - 1] == ' ')
--vmax;
+ if (!vmax)
+ vskip = NULL;
mmax = sizeof(devinfo->model);
mskip = model;
@@ -449,27 +451,45 @@ static struct scsi_dev_info_list
*scsi_dev_info_list_find(const char *vendor,
}
while (mmax > 0 && mskip[mmax - 1] == ' ')
--mmax;
+ if (!mmax)
+ mskip = NULL;
list_for_each_entry(devinfo, _table->scsi_dev_info_list,
dev_info_list) {
if (devinfo->compatible) {
/*
-* Behave like the older version of get_device_flags.
+* vendor strings must be an exact match
*/
- if (memcmp(devinfo->vendor, vskip, vmax) ||
- (vmax < sizeof(devinfo->vendor) &&
- devinfo->vendor[vmax]))
+ if (vmax != strlen(devinfo->vendor))
continue;
- if (memcmp(devinfo->model, mskip, mmax) ||
- (mmax < sizeof(devinfo->model) &&
- devinfo->model[mmax]))
+ if (vskip && vmax &&
+ memcmp(devinfo->vendor, vskip, vmax))
continue;
- return devinfo;
+ /*
+* Empty model strings only match if both strings
+* are empty.
+*/
+ if (!mmax && !strlen(devinfo->model))
+ return devinfo;
+
+ /*
+* Empty @model never matches
+*/
+ if (!mskip)
+ continue;
+
+ /*
+* @model specifies the full string, and
+* must be larger or equal to devinfo->model
+*/
+ if (!memcmp(devinfo->model, mskip,
+ strlen(devinfo->model)))
+ return devinfo;
} else {
if (!memcmp(devinfo->vendor, vendor,
-sizeof(devinfo->vendor)) &&
-!memcmp(devinfo->model, model,
- sizeof(devinfo->model)))
+ sizeof(devinfo->vendor)) &&
+ !memcmp(devinfo->model, model,
+ sizeof(devinfo->model)))
return devinfo;
}
}
--
1.8.5.6
