adduser/passwd: too long username

tito farmatito at tiscali.it
Tue Aug 5 12:42:13 UTC 2014


On Tuesday 05 August 2014 14:27:57 you wrote:
> I disagree. There is nothing to reject here. It fixes _my issue_ at hand.
> If you want to fix other bugs in your system that you are facing in
> reality, by all means, fix them in a separate change.
> 
> I definitely do not agree with dynamically allocated buffer for the simple
> reasons of:
> 
> 1) Slow.
> 2) You would still need a maximum anyway.
> 3) Needless code complication.
> 
> Let us keep things simple and good, you know the good old KISS principle.
> 
> P.S.: please do not bikeshed.
> 
> 
> On Tue, Aug 5, 2014 at 1:17 PM, tito <farmatito at tiscali.it> wrote:
> 
> > On Tuesday 05 August 2014 12:46:08 you wrote:
> > > Here is my tested fix without being to debug the busybox code, so only
> > code
> > > reading and understanding were my friends:
> > >
> > > commit 9610650b6ce2a4c1904f78a2dcdb47cad3d2e3d1
> > > Author: Laszlo Papp <lpapp at kde.org>
> > > Date:   Tue Aug 5 11:42:24 2014 +0100
> > >
> > >     Allow 256 bytes long usernames as per Unix standards (usually)
> > >
> > > diff --git a/libpwdgrp/pwd_grp.c b/libpwdgrp/pwd_grp.c
> > > index 2060d78..368c252 100644
> > > --- a/libpwdgrp/pwd_grp.c
> > > +++ b/libpwdgrp/pwd_grp.c
> > > @@ -23,8 +23,8 @@
> > >  /**********************************************************************/
> > >  /* Sizes for statically allocated buffers. */
> > >
> > > -#define PWD_BUFFER_SIZE 256
> > > -#define GRP_BUFFER_SIZE 256
> > > +#define PWD_BUFFER_SIZE LOGIN_NAME_MAX+256
> > > +#define GRP_BUFFER_SIZE LOGIN_NAME_MAX+256
> > >
> > >  /**********************************************************************/
> > >  /* Prototypes for internal functions. */
> > >
> >
> > Hi,
> > yes I've thought also about this solution but rejected it because:
> >
> > 1) there will not be enough space to hold the home dir if named the same
> > as the user
> >     so you need at least:
> >
> > #define PWD_BUFFER_SIZE LOGIN_NAME_MAX+ 6 (for home) + LOGIN_NAME_MAX (or
> > PATH_MAX?) + 256 (for the rest)
> >
> >    yet this might not be enough as in my passwd file I see a 101 char long
> > passwd.
> >    Add  the gecos fields (arbitrary lenght)  to it and the default shell
> > and we are short on space again.
> >
> > 2) same for #define GRP_BUFFER_SIZE LOGIN_NAME_MAX+256:
> >     here you need to take into account the group member list with
> >     an arbitrary number of members:
> >
> >
> >     #define GRP_BUFFER_SIZE LOGIN_NAME_MAX+256+ LOGIN_NAME_MAX*n:
> >
> > The only clean solution to fix it forever is dynamically allocated buffers
> > created at the time you read in the line from the passwd files.
> >
> > Ciao,
> > Tito
> >
> >
> > P.S.: please don't top post.
> >
> >
> > >
> > > On Tue, Aug 5, 2014 at 11:22 AM, Laszlo Papp <lpapp at kde.org> wrote:
> > >
> > > > Yeah, mayhaps... Thanks for the prompt reply. I tried to debug the
> > code,
> > > > but the busybox code here is a bit messy heavily abusing macros in C
> > and
> > > > all that. It ain't easy I must confess!
> > > >
> > > > For instance, see this section:
> > > >
> > > > http://git.busybox.net/busybox/tree/libpwdgrp/pwd_grp.c#n227
> > > >
> > > > The _source_ is included several times always getting a new meaning
> > based
> > > > on some defines... Now, check this function:
> > > >
> > > >  http://git.busybox.net/busybox/tree/libpwdgrp/pwd_grp_internal.c#n20
> > > >
> > > > "resultbuf" will be always different depending on which include it is.
> > > > Since it is failing at the pw_name check in there, I wanted to print it
> > > > out, but no easy joy there as printing it like that will yield
> > compilation
> > > > error when the file is being included next time from above.
> > > >
> > > > Right, I thought instead of doing some "#if a == b" hackery, debugging
> > > > would be easier, BUT:
> > > >
> > > > 1) The default build is stripped, yuck!
> > > >
> > > > 2) The unstripped build cannot locate the symbols (*).
> > > >
> > > > So, I am giving up on this for now; this is not the type of source code
> > > > that is so pleasant to work with. ;-)
> > > >
> > > > Cheers, L.
> > > >
> > > > * (gdb) b main
> > > >
> > > > Breakpoint 2 at 0x407c71
> > > > (gdb) r
> > > > Starting program: /home/lpapp/Projects/busybox/busybox_unstripped
> > deluser
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > > warning: Could not load shared library symbols for linux-vdso.so.1.
> > > > Do you need "set solib-search-path" or "set sysroot"?
> > > >
> > > > Breakpoint 2, 0x0000000000407c71 in main ()
> > > > (gdb) list
> > > > No symbol table is loaded.  Use the "file" command.
> > > > (gdb)
> > > >
> > > >
> > > >
> > > > On Mon, Aug 4, 2014 at 10:40 PM, tito <farmatito at tiscali.it> wrote:
> > > >
> > > >> On Monday 04 August 2014 19:06:39 Laszlo Papp wrote:
> > > >> > Hi,
> > > >> >
> > > >> > sudo busybox adduser
> > > >> >
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > >> > passwd: unknown user
> > > >> >
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > >> >
> > > >> > Yet, the user is created in /etc/shadow:
> > > >> >
> > > >> >
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff:!:16286:0:99999:7:::
> > > >> >
> > > >> > This is at least one issue, but there is another here:
> > > >> >
> > > >> > sudo busybox deluser
> > > >> >
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > >> > deluser: unknown user
> > > >> >
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > >> >
> > > >> > So, basically, once you create that long username, you cannot
> > remove it
> > > >> > anymore with busybox and it keeps polluting your system.
> > > >> >
> > > >> > You have to gain other means to clean up! I am using this version
> > over
> > > >> here:
> > > >> >
> > > >> > BusyBox v1.22.1 (2014-06-02 14:47:37 MSK) multi-call binary.
> > > >> >
> > > >> > Could you please look into this and potentially fix it? Thanks in
> > > >> advance.
> > > >> >
> > > >> > Cheers, L.
> > > >> >
> > > >> Hi,
> > > >> if disabling libb's internal pwd/grp lib and by jumping through some
> > hops
> > > >> it
> > > >> works for me:
> > > >>
> > > >> I need to add the group first as my system's groupadd command called
> > by
> > > >> bb's adduser
> > > >> supports only groupnames of max 32 chars.
> > > >>
> > > >> ./busybox addgroup
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > >> ./busybox adduser
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > >> -G
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > >> Adding user
> > > >>
> > `fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff'
> > > >> to group
> > > >>
> > `fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff'
> > > >> ...
> > > >> Adding user
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > >> to group
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > >> Done.
> > > >> Enter new UNIX password:
> > > >> Retype new UNIX password:
> > > >> passwd: password updated successfully
> > > >>
> > > >> and then I could also delete it:
> > > >>
> > > >> ./busybox deluser
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > >> ./busybox delgroup
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > >> delgroup: unknown group
> > > >>
> > fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
> > > >>
> > > >> (deluser correctly deleted also the group)
> > > >>
> > > >> I suspect that the buffer size used in libbpwdgrp/pwd_grp.c is to
> > small:
> > > >>
> > > >> #define PWD_BUFFER_SIZE 256
> > > >> #define GRP_BUFFER_SIZE 256
> > > >>
> > > >> as it is meant for the whole struct pw passwd (or struct gr group)
> > fields
> > > >> which could be easily be bigger:
> > > >>
> > > >> grep ffff* /etc/shadow | wc
> > > >>       1       1     240
> > > >> grep ffff* /etc/passwd | wc
> > > >>       1       2     286
> > > >>
> > > >> I think that the buffers' size must be increased for example to:
> > > >>
> > > >> #define PWD_BUFFER_SIZE LOGIN_NAME_MAX+LOGIN_NAME_MAX+256
> > > >>
> > > >> we need one LOGIN_NAME_MAX size for the login and one more for the
> > home
> > > >> dir
> > > >> if same as login, plus 256 for the remaining data (passwd, gecos,
> > shell,
> > > >> etc).
> > > >>
> > > >> #define GRP_BUFFER_SIZE  LOGIN_NAME_MAX+256+LOGIN_NAME_MAX*n (?)
> > > >>
> > > >> we need one LOGIN_NAME_MAX size for the group name (for which we
> > > >> actually enforce the same size as for the username) plus 256 for the
> > > >> remaining data
> > > >> plus LOGIN_NAME_MAX * n group member names.
> > > >>
> > > >> So for my limited understanding using static buffers here is rather
> > > >> difficult
> > > >> as the size of data is not easily predictable.
> > > >> I don't know how real libc manages it (maybe realloc on ERANGE?)
> > > >>
> > > >> Your particular example for me is fixed by using.
> > > >>
> > > >> #define PWD_BUFFER_SIZE 1024
> > > >>
> > > >> #define GRP_BUFFER_SIZE 1024
> > > >>
> > > >> But to me it seems not an optimal solution,
> > > >> so other more experienced developers should
> > > >> take a look at it.
> > > >>
> > > >> Hope this helps.
> > > >> Ciao,
> > > >> Tito
> > > >>
> > > >> PS: in libbbpwdgrp functions we need to check for errors:
> > > >>
> > > >>    0 or ENOENT or ESRCH or EBADF or EPERM or ...
> > > >>               The given name or gid was not found.
> > > >>
> > > >>        EINTR  A signal was caught.
> > > >>
> > > >>        EIO    I/O error.
> > > >>
> > > >>        EMFILE The maximum number (OPEN_MAX) of files was open already
> > in
> > > >> the calling process.
> > > >>
> > > >>        ENFILE The maximum number of files was open already in the
> > system.
> > > >>
> > > >>        ENOMEM Insufficient memory to allocate group structure.
> > > >>
> > > >>        ERANGE Insufficient buffer space supplied.
> > > >>
> > > >> as for example the xgroup_study function in the addgroup applet
> > > >> assigns a wrong gid if getgrgid fails for example for ERANGE
> > > >>
> > > >>         /* Check if the desired gid is free
> > > >>          * or find the first free one */
> > > >>         while (1) {
> > > >>                 printf("gid %d\n", g->gr_gid);
> > > >>                 if (!getgrgid(g->gr_gid)) {
> > > >>                         return; /* found free group: return */
> > > >>                 }
> > > >>
> > > >>
Hi,
I doubt it fixes your issue because I tested the same fix and it did in fact
fail. Please test:

1) ./busybox addgroup LONGUSERNAME   (this fails in subtle ways as a already in use gid is assigned)
2) ./busybox adduser LONGUSERNAME -G LONGUSERNAME
3) ./busybox deluser LONGUSERNAME
4) ./busybox delgroup LONGUSERNAME

Ciao,
Tito


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