[Samba] Crash in 4.12.10 in (also 4.13.4)

Tue Jan 26 19:16:37 UTC 2021

One way to force this to happen (for me atleast) is to simply kill winbindd and restart it (without restarting smbd).

A wild guess is that the pipe between smbd & winbindd being used for the communication gets closed prematurely and then some buffer that was supposed to contain some result from winbindd contains just NUL’s - which matches ID_TYPE_NOT_SPECIFIED (0)…

Anyway, I’ve uploaded a small patch that makes this function a bit more robust and so far my sambas behave better..
It’s available in the bugzilla:

  https://bugzilla.samba.org/show_bug.cgi?id=14571 <https://bugzilla.samba.org/show_bug.cgi?id=14571>

- Peter

> On 26 Jan 2021, at 14:32, Peter Eriksson via samba <samba at lists.samba.org <mailto:samba at lists.samba.org>> wrote:
> 
> Added an assert that checks if we over-run the wbc_sids[] array and now 4.13.4 dies immediately when I try it.
> 
> Looking at the code, the suspicious code is around line 1277 in source3/passwd/lookup_sid.c:
> 
> 
>                if (sid_peek_check_rid(&global_sid_Unix_Groups,
>                                       &sids[i], &rid)) {
>                        ids[i].type = ID_TYPE_GID;
>                        ids[i].id = rid;
>                        continue;
>                }
> —>          if (idmap_cache_find_sid2unixid(&sids[I], &ids[i], &expired)
>                    && !expired)
>                {
>                        continue;
>                }
>                ids[i].type = ID_TYPE_NOT_SPECIFIED;
>                memcpy(&wbc_sids[num_not_cached], &sids[i],
>                       ndr_size_dom_sid(&sids[i], 0));
>                num_not_cached += 1;
> 
> If that idmap_cache_find() call, or !expired is true - and ids[I].type happens to already be ID_TYPE_NOT_SPECIFIED then num_not_cached will not be incremented, but the loop further down will detect it and then the buffer overrun will happen…
> 
> - Peter
> 
> 
> 
>> On 26 Jan 2021, at 13:04, Peter Eriksson via samba <samba at lists.samba.org <mailto:samba at lists.samba.org> <mailto:samba at lists.samba.org <mailto:samba at lists.samba.org>>> wrote:
>> 
>> It seems to be crashing in source3/passwd/lookup_sids.c line 1307:
>> 
>>>  switch (wbc_ids[num_not_cached].type) {
>> 
>> Due it trying to access outside the allocated data area…
>> 
>> (gdb) print num_not_cached
>> $23 = 68
>> (gdb) print num_sids
>> $24 = 245
>> (gdb) print wbc_ids[66]
>> $21 = {type = WBC_ID_TYPE_NOT_SPECIFIED, id = {uid = 0, gid = 0}}
>> (gdb) print wbc_ids[67]
>> $22 = {type = WBC_ID_TYPE_NOT_SPECIFIED, id = {uid = 48, gid = 48}}
>> (gdb) print wbc_ids[68]
>> Cannot access memory at address 0x81b339000
>> 
>> wbc_ids is talloc_array():n at line 1290, but unfortunately the num_not_cached variable is reused so I can’t in the core dump see how many entries actually was allocated there. I’ll recompile add a debugging assertion check to see what’s happening there.
>> 
>> The user that was connected to the smbd at the time of the crash is a member of some 90 AD groups, of which 24 has gidNumber set. Dunno if that’s relevant for this case but anyway.
>> 
>> I’ll try to do some more debugging.
>> 
>> https://bugzilla.samba.org/show_bug.cgi?id=14571 <https://bugzilla.samba.org/show_bug.cgi?id=14571> <https://bugzilla.samba.org/show_bug.cgi?id=14571 <https://bugzilla.samba.org/show_bug.cgi?id=14571>> <https://bugzilla.samba.org/show_bug.cgi?id=14571 <https://bugzilla.samba.org/show_bug.cgi?id=14571> <https://bugzilla.samba.org/show_bug.cgi?id=14571 <https://bugzilla.samba.org/show_bug.cgi?id=14571>>>
>> 
>> - Peter
>> 
>> 
>> 
>>> On 11 Nov 2020, at 12:43, Andrew Walker via samba <samba at lists.samba.org <mailto:samba at lists.samba.org> <mailto:samba at lists.samba.org <mailto:samba at lists.samba.org>> <mailto:samba at lists.samba.org <mailto:samba at lists.samba.org> <mailto:samba at lists.samba.org <mailto:samba at lists.samba.org>>>> wrote:
>> 
>>> On Tue, Nov 10, 2020 at 5:01 PM Peter Eriksson via samba <
>>> samba at lists.samba.org <mailto:samba at lists.samba.org> <mailto:samba at lists.samba.org <mailto:samba at lists.samba.org>> <mailto:samba at lists.samba.org <mailto:samba at lists.samba.org> <mailto:samba at lists.samba.org <mailto:samba at lists.samba.org>>>> wrote:
>>> 
>>>> I just got an INTERNAL ERROR: Signal 11 in smbd (4.12.10) in something
>>>> that sids_to_unixids() in source3/winbindd/idmap_hash/idmap_has.c calls and
>>>> 3 levels down - unfortunately the stack trace doesn’t say what it is -
>>>> probably optimised into inline code or something.
>>>> 
>>>> Recently upgraded from Samba 4.12.5 to 4.12.10 (self-compiled). FreeBSD
>>>> 12.2
>>>> 
>>>> It happened right after 10 hours since that smbd processes started so the
>>>> 10 hours Kerberos ticket lifetime is probably involved somehow…
>>>> 
>>>> Nov 10 21:39:11 runur01 smbd_audit[23768]:    #3 sig_fault + 0x6c
>>>> [ip=0x80129a7a9] [sp=0x7fffffffcbb0]
>>>> Nov 10 21:39:11 runur01 smbd_audit[23768]:    #4 <unknown symbol>
>>>> [ip=0x801517b70] [sp=0x7fffffffcbc0]
>>>> Nov 10 21:39:12 runur01 smbd_audit[23768]:    #5 <unknown symbol>
>>>> [ip=0x80151713f] [sp=0x7fffffffcf80]
>>>> Nov 10 21:39:12 runur01 smbd_audit[23768]:    #6 <unknown symbol>
>>>> [ip=0x7ffffffff003] [sp=0x7fffffffcff0]
>>>> Nov 10 21:39:12 runur01 smbd_audit[23768]:    #7 sids_to_unixids + 0x25d
>>>> 
>>>> Unfortunately no core dump :-(
>>>> 
>>> You may need to run the command "sysctl kern.sugid_coredump=1" and also set
>>> kern.corefile to an appropriate path (for example /tmp/%N_%P.core -- this
>>> ensures program name and pid are in corefile name).  If possible compile
>>> without optimizations and with debugging symbols (this will improve
>>> visibility of error).
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