[systemd-devel] [EXT] Initialization of "vbuf" in function "token_match_attr"

[Amit anand]

Hi,

On Tue, Sep 8, 2020 at 6:23 PM Ulrich Windl <
Ulrich.Windl at rz.uni-regensburg.de> wrote:

> Hi!
>
> vbuf is initialized: It has some address on the stack, so "if (value !=
> vbuf)" is comparing adresses, if I got it right...
>
vbuf having some address on stack and "if(value!=vbuf)" is comparing
addresses doesn't necessarily implies that vbuf is initialized.
I am still not clear about where vbuf is initialized.
Also, expecting some information regarding my queries in below mail.

Thanks,
Amit

>
> >>> Amit anand <amit.table at gmail.com> schrieb am 08.09.2020 um 13:56 in
> Nachricht
> <CAMkFpM5NFmN+pc_cztmMZW=j1vn2RYC16AgJ3LYL6RSgdqP1eA at mail.gmail.com>:
> > Hi systemd-devel team,
> >
> > I am trying to understand where "vbuf" is initialized in function
> > "token_match_attr()" in file udev-rules.c
> >
> > Below code snippet :
> > static bool* token_match_attr*(UdevRuleToken *token, sd_device *dev,
> > UdevEvent *event) {
> >  *char* nbuf[UTIL_NAME_SIZE], *vbuf*[UTIL_NAME_SIZE];     // Here, vbuf
> is
> > defined, however not initialized.
> > *const char* *name, **value;        *// Here, value is declared to be of
> > type const char *, however, not initialized.
> > ...
> > ... // some code
> > ...
> > switch (token->attr_subst_type) {   // *Event 1* : This evaluates to
> > SUBST_TYPE_PLAIN
> > ...
> > case *SUBST_TYPE_PLAIN*:   if (sd_device_get_sysattr_value(dev, name,
> > &value) < 0)   // *Event 2* :The if condition evaluates to false.
> >                                                  return false;
> >  break;
> > ...// some code
> > ...
> > }
> >
> >         if (token->attr_match_remove_trailing_whitespace) {      //
> *Event
> > 4*: If condition evaluates to true
> >                 if (value != vbuf) {      //  *Event 5* : vbuf and value
> > are both declared but not initialized. Comparison is done without
> > initializing "vbuf" and "value".
> >                         strscpy(vbuf, sizeof(vbuf), value);
> >                         value = vbuf;
> >                 } // End of if.
> >
> >                 delete_trailing_chars(vbuf, NULL);         // *Event 6*:
> > trying to delete trailing chars from "vbuf" which is not initialzed. ??
> >         } // End of outer if.
> > ... // some code
> > } /End of function : *token_match_attr()*
> >
> > Below are my queries :
> > 1. *Event 5 *above, we are comparing two resources ("value" and "vbuf")
> > even before initializing them.
> >     Are we doing this comparision to do decision making based on whether
> > the pointer type variable "value" is pointing to "vbuf" or not.
> > *Query*: Kindly confirm whether my understanding is correct.
> >
> > 2. *Event 6* above, delete_trailing_chars(vbuf, NULL) is called outside
> *if
> > (value != vbuf).*
> >     This implies there may occur a situation where:
> >               step 1 ) *if (value != vbuf) *condition fails  --> step 2 )
> > *vbuf* is not initialzed inside the *if(value != vbuf)  *--> step 3 )
> > delete_trailing_chars(*vbuf*, NULL).
> > Here, delete_trailing_chars() called for "*vbuf*" which is not
> necessarily
> > initiazlied.
> > *Query*: Kindly let me know if my understanding is correct or I am
> missing
> > something.
> >
> > Thanks,
> > Amit
>
>
>
>
>
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