[Toybox] ls -Z with relative paths

[enh]

On Mon, Jan 11, 2016 at 1:17 PM, Rob Landley <rob at landley.net> wrote:
> On 01/09/2016 03:38 PM, enh wrote:
>> i have the following internal bug:
>>
>> ls -laZ doesn't properly return the SELinux label for files where a
>> non-fully qualified path is provided.
>>
>> Steps to reproduce (on Nexus 9):
>>
>>   adb shell ls -laZ /sys/kernel/debug/tracing/tracing_on
>>   adb shell ls -laZ /sys/kernel/debug/tracing/ | grep tracing_on
>>   adb shell 'cd /sys/kernel/debug/tracing ; ls -laZ tracing_on'
>>
>> Expected: The output of all commands should yield the same SELinux
>> label: "u:object_r:debugfs_tracing:s0"
>
> I have now ordered a 1 gig quad processor raspberry pi "b" to try to
> fling marshmallow upon. (I really need an android test environment, and
> that's powerful enough to potentially self-host, so...)
>
> (I would have ordered a b+ but those are all 512M with 700 mhz processor
> and I think it's only dual core... Not sure how "+" works into it here.)

(i realize you probably just wanted an excuse to buy a Raspberry Pi,
but the x86 emulator using kvm is very fast, you know.)

>> something like this seems sensible for ls:
>>
>> diff --git a/toys/posix/ls.c b/toys/posix/ls.c
>> index 2f44d24..08ae695 100644
>> --- a/toys/posix/ls.c
>> +++ b/toys/posix/ls.c
>> @@ -541,6 +541,7 @@ void ls_main(void)
>>    // Iterate through command line arguments, collecting directories and files.
>>    // Non-absolute paths are relative to current directory.
>>    TT.files = dirtree_start(0, 0);
>> +  TT.files->dirfd = AT_FDCWD;
>>    for (s = *toys.optargs ? toys.optargs : noargs; *s; s++) {
>>      dt = dirtree_start(*s, !(toys.optflags&(FLAG_l|FLAG_d|FLAG_F)) ||
>>                              (toys.optflags&(FLAG_L|FLAG_H)));
>
> Yes, that's the correct fix. (I just independently did that before
> noticing the second half of your message. :)

not sure whether you mean you've already applied a fix but not pushed,
but in case you haven't, patch attached.

>> but i'm not sure whether the semantics of dirtree_start are supposed
>> to imply this? certainly defaulting dirfd to -1 rather than 0 might
>> lead to fewer surprises in future.
>
> The ls recursion is unusual because ls's recursion semantics are funky.
> (It does two passes over the data to pad out columns, the "label this
> directory or not" logic involves knowledge of other arguments, and so on.)
>
> So to implement what posix wants, ls takes manual control over recursion
> (calling dirtree_recurse() itself in listfiles()), which uses mostly the
> same data structure and mostly the same functions, but just... connects
> them up strangely so it can do crazy things that straddle nodes.
>
> This is why there's a fake node at the top of the ls tree representing
> ".", which is not usually the case. (The manual recursion in ls requires
> a parent node to operate, the common infrastructure doesn't). So our
> "did we fall off the top of the tree logic and have no ->parent,
> therefore AT_CWD" logic doesn't trigger, and sticking AT_CWD into the
> fake top of tree node as its dirfd is the correct response.
>
> Rob



-- 
Elliott Hughes - http://who/enh - http://jessies.org/~enh/
Android native code/tools questions? Mail me/drop by/add me as a reviewer.
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