efivarfs: Bad directory entry when variable has / in name

efivarfs: Bad directory entry when variable has / in name

[shea-yfkUTty7RcRWk0Htik3J/w]

Hello,

When there is an EFI variable with a forward slash in its name, 
/sys/firmware/efi/efivars contains a directory entry with a forward 
slash, which of course causes all sorts of problems (e.g. EINVAL from 
stat(2)). Off the top of my head, I can think of two ways to handle 
this:

1. Simply skip such variables when making the sysfs entries
2. Come up with an escaping scheme, e.g. "a single backslash is 
actually a forward slash, two backslashes are actually a single 
backslash" or some such.

Thoughts?

Cheers,
Shea Levy

P.S. Here is the program I ran to get the problematic efi variable, 
which worked on qemu+OMVF and a macbook pro 9,2:

EFI_STATUS EFIAPI Main(
                 IN EFI_HANDLE ImageHandle,
                 IN EFI_SYSTEM_TABLE *SystemTable
                 )
{
         EFI_GUID var_guid = { 0x38bd6e09, 0x70b3, 0x48f0, {0x8e, 0xa2, 
0x87, 0x25, 0x0c, 0xc3, 0x27, 0x71} };
         CHAR16 *var_name = L"a/directory";
         CHAR8 data = '\0';
         EFI_STATUS status;

         return SystemTable->RuntimeServices->SetVariable(
                         var_name,
                         &var_guid,
                         
EFI_VARIABLE_BOOTSERVICE_ACCESS|EFI_VARIABLE_RUNTIME_ACCESS,
                         sizeof data,
                         &data
                         );
}

Re: efivarfs: Bad directory entry when variable has / in name

[Matt Fleming]

On 03/19/2013 08:36 PM, shea-yfkUTty7RcRWk0Htik3J/w@public.gmane.org wrote:
> Hello,
> 
> When there is an EFI variable with a forward slash in its name, 
> /sys/firmware/efi/efivars contains a directory entry with a forward 
> slash, which of course causes all sorts of problems (e.g. EINVAL from 
> stat(2)). Off the top of my head, I can think of two ways to handle 
> this:
> 
> 1. Simply skip such variables when making the sysfs entries
> 2. Come up with an escaping scheme, e.g. "a single backslash is 
> actually a forward slash, two backslashes are actually a single 
> backslash" or some such.
> 
> Thoughts?

Right. Have you seen machines with such variable names in the wild?
There's nothing in the specification that prohibits the use of slashes
in variable names, so I'm not in favour of option 1 above and mangling
the variable name would likely cause too much confusion.

The best solution I can come up with is to create directories for any
variable names that contain "/" (which would also make it possible to
build filesystem hierarchies with EFI variables). The user could choose
to ignore the actual layout of the filesystem since opening the variable
"adirectory/file" with,

	open("adirectory/file-<guid>");

would work without it being necessary for the user to handle slashes in
variable names.

What do you think?

Presumably this is also an issue with the old EFI vars sysfs code?

-- 
Matt Fleming, Intel Open Source Technology Center

Re: efivarfs: Bad directory entry when variable has / in name

[shea-yfkUTty7RcRWk0Htik3J/w]

On 2013-03-20 04:41, Matt Fleming wrote:
> On 03/19/2013 08:36 PM, shea-yfkUTty7RcRWk0Htik3J/w@public.gmane.org wrote:
>> Hello,
>>
>> When there is an EFI variable with a forward slash in its name,
>> /sys/firmware/efi/efivars contains a directory entry with a forward
>> slash, which of course causes all sorts of problems (e.g. EINVAL 
>> from
>> stat(2)). Off the top of my head, I can think of two ways to handle
>> this:
>>
>> 1. Simply skip such variables when making the sysfs entries
>> 2. Come up with an escaping scheme, e.g. "a single backslash is
>> actually a forward slash, two backslashes are actually a single
>> backslash" or some such.
>>
>> Thoughts?
>
> Right. Have you seen machines with such variable names in the wild?
>

No, I just thought of testing it when I saw that variable names only 
require null termination.

>
> There's nothing in the specification that prohibits the use of 
> slashes
> in variable names, so I'm not in favour of option 1 above and 
> mangling
> the variable name would likely cause too much confusion.
>
> The best solution I can come up with is to create directories for any
> variable names that contain "/" (which would also make it possible to
> build filesystem hierarchies with EFI variables). The user could 
> choose
> to ignore the actual layout of the filesystem since opening the 
> variable
> "adirectory/file" with,
>
> 	open("adirectory/file-<guid>");
>
> would work without it being necessary for the user to handle slashes 
> in
> variable names.
>
> What do you think?
>

What happens when I create a variable starting with a slash or ending 
with a slash, or something like "dir/../../../../root/private-file"? 
Also, how would you create such a variable from linux, mkdir followed by 
creating the file?

Looks like an escaping scheme (though of course my proposed one was 
braindead and wouldn't work) might be the best option here, I might spin 
up a patch this weekend.

>
> Presumably this is also an issue with the old EFI vars sysfs code?

Never used that directly myself (only through efibootmgr).

Cheers,
Shea Levy