Re: + libfs-fix-error-format-in-simple_attr_write.patch added to mm-nonmm-unstable branch

Re: + libfs-fix-error-format-in-simple_attr_write.patch added to mm-nonmm-unstable branch

[Alexey Dobriyan]

On Thu, Sep 15, 2022 at 02:34:25PM -0700, Andrew Morton wrote:
>      libfs-fix-error-format-in-simple_attr_write.patch

> From: Eliav Farber <farbere@amazon.com>
> Subject: libfs: fix error format in simple_attr_write()
> Date: Thu, 15 Sep 2022 09:15:44 +0000
> 
> In commit 488dac0c9237 ("libfs: fix error cast of negative value in
> simple_attr_write()"), simple_attr_write() was changed to use kstrtoull()
> instead of simple_strtoll() to convert a string got from a user.  A user
> trying to set a negative value will get an error.
> 
> This is wrong since it breaks all the places that use
> DEFINE_DEBUGFS_ATTRIBUTE() with format of a signed integer.
> 
> For the record there are 43 current users of signed integer which are
> likely to be effected by this:
> 
> $ git grep -n -A1 -w DEFINE_DEBUGFS_ATTRIBUTE | grep ');' |
> sed 's,.*\(".*%.*"\).*,\1,' | sort | uniq -c
>   1 "%08llx\n"
>   5 "0x%016llx\n"
>   5 "0x%02llx\n"
>   5 "0x%04llx\n"
>  13 "0x%08llx\n"
>   1 "0x%4.4llx\n"
>   3 "0x%.4llx\n"
>   4 "0x%llx\n"
>   1 "%1lld\n"
>  40 "%lld\n"
>   2 "%lli\n"
> 129 "%llu\n"
>   1 "%#llx\n"
>   2 "%llx\n"
> 
> u64 is not an issue for negative numbers.
> The %lld and %llu in any case are for 64-bit value, representing it as
> unsigned simplifies the generic code, but it doesn't mean we can't keep
> their signed value if we know that.
> 
> This change uses sscanf() to fix the problem since it does the conversion
> based on the supplied format string.

> --- a/fs/libfs.c~libfs-fix-error-format-in-simple_attr_write
> +++ a/fs/libfs.c
> @@ -1017,9 +1017,12 @@ ssize_t simple_attr_write(struct file *f
>  		goto out;
>  
>  	attr->set_buf[size] = '\0';
> -	ret = kstrtoull(attr->set_buf, 0, &val);
> -	if (ret)
> +	ret = sscanf(attr->set_buf, attr->fmt, &val);
> +	if (ret != 1) {
> +		ret = -EINVAL;
>  		goto out;
> +	}
> +
>  	ret = attr->set(attr->data, val);
>  	if (ret == 0)
>  		ret = len; /* on success, claim we got the whole input */

No scanf please. Just revert original patch if something broke.

scanf may be tolerable if it is just one format conversion but it is
disaster as an interface.

Re: + libfs-fix-error-format-in-simple_attr_write.patch added to mm-nonmm-unstable branch

[Farber, Eliav]

On 9/16/2022 9:11 AM, Alexey Dobriyan wrote:
> On Thu, Sep 15, 2022 at 02:34:25PM -0700, Andrew Morton wrote:
>> libfs-fix-error-format-in-simple_attr_write.patch
>
>> From: Eliav Farber <farbere@amazon.com>
>> Subject: libfs: fix error format in simple_attr_write()
>> Date: Thu, 15 Sep 2022 09:15:44 +0000
>>
>> In commit 488dac0c9237 ("libfs: fix error cast of negative value in
>> simple_attr_write()"), simple_attr_write() was changed to use 
>> kstrtoull()
>> instead of simple_strtoll() to convert a string got from a user.  A user
>> trying to set a negative value will get an error.
>>
>> This is wrong since it breaks all the places that use
>> DEFINE_DEBUGFS_ATTRIBUTE() with format of a signed integer.
>>
>> For the record there are 43 current users of signed integer which are
>> likely to be effected by this:
>>
>> $ git grep -n -A1 -w DEFINE_DEBUGFS_ATTRIBUTE | grep ');' |
>> sed 's,.*\(".*%.*"\).*,\1,' | sort | uniq -c
>>   1 "%08llx\n"
>>   5 "0x%016llx\n"
>>   5 "0x%02llx\n"
>>   5 "0x%04llx\n"
>>  13 "0x%08llx\n"
>>   1 "0x%4.4llx\n"
>>   3 "0x%.4llx\n"
>>   4 "0x%llx\n"
>>   1 "%1lld\n"
>>  40 "%lld\n"
>>   2 "%lli\n"
>> 129 "%llu\n"
>>   1 "%#llx\n"
>>   2 "%llx\n"
>>
>> u64 is not an issue for negative numbers.
>> The %lld and %llu in any case are for 64-bit value, representing it as
>> unsigned simplifies the generic code, but it doesn't mean we can't keep
>> their signed value if we know that.
>>
>> This change uses sscanf() to fix the problem since it does the 
>> conversion
>> based on the supplied format string.
>
>> --- a/fs/libfs.c~libfs-fix-error-format-in-simple_attr_write
>> +++ a/fs/libfs.c
>> @@ -1017,9 +1017,12 @@ ssize_t simple_attr_write(struct file *f
>>               goto out;
>>
>>       attr->set_buf[size] = '\0';
>> -     ret = kstrtoull(attr->set_buf, 0, &val);
>> -     if (ret)
>> +     ret = sscanf(attr->set_buf, attr->fmt, &val);
>> +     if (ret != 1) {
>> +             ret = -EINVAL;
>>               goto out;
>> +     }
>> +
>>       ret = attr->set(attr->data, val);
>>       if (ret == 0)
>>               ret = len; /* on success, claim we got the whole input */
>
> No scanf please. Just revert original patch if something broke.
>
> scanf may be tolerable if it is just one format conversion but it is
> disaster as an interface.


If I revert original patch I get this checkpatch warning:
"WARNING: simple_strtoll is obsolete, use kstrtoll instead".

Should I still revert the original patch as is, or send a new patch that
fixes the issue by using kstrtoll()?

--
Thanks, Eliav

Re: + libfs-fix-error-format-in-simple_attr_write.patch added to mm-nonmm-unstable branch

[Andrew Morton]

On Fri, 16 Sep 2022 14:19:29 +0300 "Farber, Eliav" <farbere@amazon.com> wrote:

> Should I still revert the original patch as is, or send a new patch that
> fixes the issue by using kstrtoll()?

That sounds better.