Bug#1033311: sysvinit-utils: pidof not always returning a pid when using the full path to a program

[Markus Fischer]

I think I've figured it out. With the following patch I don't see the 
unexpected behaviour anymore:

--- a/src/killall5.c
+++ b/src/killall5.c
@@ -662,6 +662,7 @@ int readproc()
                 /* Try to stat the executable. */
                 snprintf(path, sizeof(path), "/proc/%s/exe", d->d_name);
                  p->pathname = (char *)xmalloc(PATH_MAX);
+               memset(p->pathname, 0, PATH_MAX);
                 if (readlink(path, p->pathname, PATH_MAX) == -1) {
                         p->pathname = NULL;
                 }

This patch gets rid of this uninitialised value warning I saw in valgrind:

==4158== Conditional jump or move depends on uninitialised value(s)
==4158==    at 0x484748D: strcmp (vg_replace_strmem.c:924)
==4158==    by 0x10A64F: pidof (killall5.c:797)
==4158==    by 0x10B2EE: main_pidof (killall5.c:1031)
==4158==    by 0x109700: main (killall5.c:1108)
==4158==  Uninitialised value was created by a heap allocation
==4158==    at 0x4840660: malloc (vg_replace_malloc.c:381)
==4158==    by 0x10AD51: xmalloc (killall5.c:170)
==4158==    by 0x10AD51: readproc (killall5.c:664)
==4158==    by 0x10B2A0: main_pidof (killall5.c:1028)
==4158==    by 0x109700: main (killall5.c:1108)

I compiled the killall5 binary with:

CFLAGS="-O2 -ggdb" make killall5



Am 23.03.23 um 16:25 schrieb Jesse Smith:
> 
> On 2023-03-23 12:04 p.m., Markus Fischer wrote:
>> I could also reproduce it with emacs. I've used emacs-gtk to avoid the
>> symlink.
>>
>> ```shell 1
>> $ emacs-gtk -nw -fn helvetica
>> ```
>>
>> ```shell 2
>> $ ./pidof emacs-gtk
>> 24727
>> $ ./pidof $(which emacs-gtk)
>> $ ls -l $(which emacs-gtk)
>> -rwxr-xr-x 1 root root 5294300 Mar 14 21:30 /usr/bin/emacs-gtk
>> ```
> This is interesting. Is there anything else you can share that might
> shed light on why this happens while I can't get the same results? You
> mentioned you're using two separate shells. Are they with the same user
> account? Is there any PID hiding feature of Debian enabled? Does it
> still happen if you run "pidof -z $(which emacs-gtk)"?