Re: [PATCH 1/2] depmod: do not allow partial matches with "search" directive

[Anssi Hannula <anssi@mageia.org>]

19.03.2014 23:22, Lucas De Marchi kirjoitti:
> On Wed, Mar 19, 2014 at 6:12 PM, Anssi Hannula <anssi@mageia.org> wrote:
>> 19.03.2014 14:24, Lucas De Marchi kirjoitti:
>>> Hi Anssi,
>>
>> Hi,
>>
>>> On Tue, Mar 18, 2014 at 8:26 PM, Anssi Hannula <anssi@mageia.org> wrote:
>>>> Currently e.g. "search foo foobar built-in" will cause unpredictable
>>>> results if baz.ko is in both foo/ and foobar/, since "foo" in search may
>>>> match both of those directories and the preferred module therefore
>>>> depends on processing order.
>>>>
>>>> Fix the code to ensure that the match is performed on full pathname
>>>> components only.
>>>> ---
>>>>  tools/depmod.c | 4 ++--
>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/tools/depmod.c b/tools/depmod.c
>>>> index 9f83ee8..328e578 100644
>>>> --- a/tools/depmod.c
>>>> +++ b/tools/depmod.c
>>>> @@ -1153,10 +1153,10 @@ static int depmod_module_is_higher_priority(const struct depmod *depmod, const s
>>>>                 DBG("search %s\n", se->builtin ? "built-in" : se->path);
>>>>                 if (se->builtin)
>>>>                         bprio = i;
>>>> -               else if (newlen >= se->len &&
>>>> +               else if (newlen > se->len && newpath[se->len] == '/' &&
>>>>                          memcmp(se->path, newpath, se->len) == 0)
>>>>                         newprio = i;
>>>> -               else if (oldlen >= se->len &&
>>>> +               else if (oldlen > se->len && oldpath[se->len] == '/' &&
>>>>                          memcmp(se->path, oldpath, se->len) == 0)
>>>>                         oldprio = i;
>>>>         }
>>>> --
>>>
>>>
>>> Both patches have been applied. Thanks a lot.
>>>
>>> I added some test cases for depmod. Could you take a look if they are ok?
>>
>> Well, just reversing the "search" directive does not ensure the bug is
>> caught by the test (and indeed it is not on my testing, i.e. tests still
>> pass after reverting my fix locally), since it does not alter the
>> initial order the modules are found.
> 
> hum... assuming the traverse order is stable, one of them should hit
> it. In fact. Reverting your commit does reproduce the bug for me 100%
> of the time.
> 
>>
>> To hit the bug, the code needs to hit the short-directory module first,
>> so that the short path is in "oldpath" and the long path is in "newpath".
> 
> But it really depends if the short is the right one as opposed to the
> long one.  Otherwise it would be correct to replace the module, even
> if by accident.

I don't think so. Let me try to show what I mean with an example with
all the 4 combinations with unfixed code:

Let's have foo/module.ko and foobar/module.ko.

Traverse order foo,foobar:
oldpath = foo/module.ko
newpath = foobar/module.ko

"search foo(2) foobar(1) built-in(0)"
iteration 0: bprio = 0
iteration 1: newprio = 1
iteration 2: newprio = 2
oldprio fallback: oldprio = 0
=> oldprio 0, newprio 2
=> WRONG

"search foobar(2) foo(1) built-in(0)"
iteration 0: bprio = 0
iteration 1: newprio = 1
iteration 2: newprio = 2
oldprio fallback: oldprio = 0
=> oldprio 0, newprio 2
=> OK


Traverse order foobar,foo:
oldpath = foobar/module.ko
newpath = foo/module.ko

"search foo(2) foobar(1) built-in(0)"
iteration 0: bprio = 0
iteration 1: oldprio = 1
iteration 2: newprio = 2
=> oldprio 1, newprio 2
=> OK

"search foobar(2) foo(1) built-in(0)"
iteration 0: bprio = 0
iteration 1: newprio = 1
iteration 2: oldprio = 2
=> oldprio 2, newprio 1
=> OK


So the bug is triggered only if the shorter name is higher-prio _and_
shorter name is traversed first. If the long name is traversed first,
the bug don't trigger with either "search" directive order (and on my
"make check" runs this is the case).


> 
> Are you testing this with "make check" or running locally on your system?

make check.

-- 
Anssi Hannula