Re: nss_winbind Segmentation fault -

[Matthias Petermann <mp%petermann-it.de@localhost>]

Hello Christos,

Thank you for your tip - I have come a little further. Am I correctly 
interpreting the debugger output that the memory address of the integer 
pointer from groupc points to empty/unallocated memory?

-------------------------------------------------------------------------
test10# gdb /usr/bin/id id.core
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Reading symbols from /usr/bin/id...
Reading symbols from /usr/libdata/debug//usr/bin/id.debug...
[New process 5161]
Core was generated by `id'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007617ee803dcf in netbsdwinbind_getgroupmembership (nsrv=0x0, 
nscb=0x0, ap=0x7f7fff209688) at ../../nsswitch/winbind_nss_netbsd.c:203
203                     for (dupc = 0; dupc < MIN(maxgrp, *groupc); 
dupc++) {
(gdb) br netbsdwinbind_getgroupmembership
Breakpoint 1 at 0x7617ee803aac: file 
../../nsswitch/winbind_nss_netbsd.c, line 176.
(gdb) run Administrator
Starting program: /usr/bin/id Administrator

Breakpoint 1, netbsdwinbind_getgroupmembership (nsrv=0x0, nscb=0x0, 
ap=0x7f7fff3af948) at ../../nsswitch/winbind_nss_netbsd.c:176
176     {
(gdb) s
177             int             *result = va_arg(ap, int *);
(gdb) s
178             const char      *uname  = va_arg(ap, const char *);
(gdb) s
179             gid_t           *groups = va_arg(ap, gid_t *);
(gdb) s
180             int              maxgrp = va_arg(ap, int);
(gdb) s
181             int             *groupc = va_arg(ap, int *);
(gdb) s
183             struct winbindd_request request = {
(gdb) p uname
$1 = 0x73209820ce60 <_winbind_passwdbuf> "MPNET\\administrator"
(gdb) x 0x73209820ce60
0x73209820ce60 <_winbind_passwdbuf>:        "MPNET\\administrator"
(gdb) p groupc
$2 = (int *) 0x732000000011
(gdb) x 0x732000000011
0x732000000011:   <error: Cannot access memory at address 0x732000000011>
-------------------------------------------------------------------------

The further backtrace looks like this:

-------------------------------------------------------------------------
(gdb) c
Continuing.

Program received signal SIGSEGV, Segmentation fault.
0x0000732098003dcf in netbsdwinbind_getgroupmembership (nsrv=0x0, 
nscb=0x0, ap=0x7f7fff3af948) at ../../nsswitch/winbind_nss_netbsd.c:203
203                     for (dupc = 0; dupc < MIN(maxgrp, *groupc); 
dupc++) {
(gdb) bt
#0  0x0000732098003dcf in netbsdwinbind_getgroupmembership (nsrv=0x0, 
nscb=0x0, ap=0x7f7fff3af948) at ../../nsswitch/winbind_nss_netbsd.c:203
#1  0x0000732098b5a375 in _nsdispatch (retval=retval@entry=0x0, 
disp_tab=disp_tab@entry=0x732098de0de0, 
database=database@entry=0x732098ba0849 "group",
	method=method@entry=0x732098b96a4e "getgroupmembership", 
defaults=0x732098de5ec0 <__nsdefaultcompat>) at 
/home/source/ab/HEAD/src/lib/libc/net/nsdispatch.c:670
#2  0x0000732098aa25f9 in _getgroupmembership 
(_uname=_uname@entry=0x73209820ce60 <_winbind_passwdbuf> 
"MPNET\\administrator", agroup=agroup@entry=100,
	groups=groups@entry=0x7320991f2050, maxgrp=17, 
groupc=groupc@entry=0x7f7fff3afb2c) at 
/home/source/ab/HEAD/src/lib/libc/gen/getgroupmembership.c:396
#3  0x0000732098a72d40 in _getgrouplist (_uname=0x73209820ce60 
<_winbind_passwdbuf> "MPNET\\administrator", agroup=100, 
groups=0x7320991f2050, grpcnt=0x7f7fff3afb88)
	at /home/source/ab/HEAD/src/lib/libc/gen/getgrouplist.c:67
#4  0x0000000086001792 in user (pw=0x73209820ce00 <_winbind_passwd>) at 
/home/source/ab/HEAD/src/usr.bin/id/id.c:272
#5  main (argc=<optimized out>, argv=<optimized out>) at 
/home/source/ab/HEAD/src/usr.bin/id/id.c:167
-------------------------------------------------------------------------

I then unpacked the appropriate current sources under /home/source... so 
that I am at least technically able to continue debugging. However, my 
understanding just stops here and I have to take more time to think 
myself into it. Can you see anything obvious from the output of gdb?

Kind regards
Matthias


Am 21.07.2020 um 01:29 schrieb Christos Zoulas:
> groupc must be NULL. You probably want to install the debug sets
> so that you can also see how libc is calling nsdispatch.
>
> christos
>
> > On Jul 20, 2020, at 7:24 PM, Matthias Petermann <mp%petermann-it.de@localhost 
> > <mailto:mp%petermann-it.de@localhost>> wrote:
> >
> > )