tony@ajfcal.UUCP (Tony Field) (06/09/89)
Is there any way to do a setuid(geteuid()) when geteuid() != 0 ??? System: Xenix 2.2.3/386. I have a shell script that is running an effective uid of "news". The script calls a process that has a real uid of a "user". The process can create directories with mkdir that belong to "user", however it cannot create a file. If the process is setuid to root, then I can create the directores and the files, however the owner becomes "root", and I would prefer the owner be "news". The shell script could pass it's uid to the process as a parameter, and the process could do a "chown" however there must be a better way: I would prefer not to run setuid root. thanks a bunch... tony.... -- +------------------------------------ | Tony Field ..uunet!utai!calgary!ajfcal!tony | Co-Design Information Systems Ltd. | Calgary, Alberta, Canada voice: (403) 266-3239
maart@cs.vu.nl (Maarten Litmaath) (06/13/89)
tony@ajfcal.UUCP (Tony Field) writes: \Is there any way to do a setuid(geteuid()) when geteuid() != 0 ??? setuid() to either geteuid() or getuid() must ALWAYS succeed. Elementary. \System: Xenix 2.2.3/386. \ \I have a shell script that is running an effective uid of "news". The \script calls a process that has a real uid of a "user". The process can \create directories with mkdir that belong to "user", however it cannot \create a file. This is due to the new effective uid OVERWRITING of the old effective uid. One might consider this a BAD feature... Now let's take a look at `mkdir': I assume your version of Xenix doesn't have the mkdir() system call, i.e. /bin/mkdir has to be setuid root. Scheme: real uid - effective uid shell script user news > program user news >> mkdir user root whereas one would like real uid - effective uid shell script user news > program user news >> mkdir news root Alas! `mkdir' will chown() the directory to `user', notwithstanding `program' having effective uid `news'! On the other hand `program' (setuid `news') cannot create FILES in the current directory, because the latter is owned by `user'. \If the process is setuid to root, then I can create the directores and \the files, however the owner becomes "root", and I would prefer the \owner be "news". [...] A solution: let the shell script invoke some `wrapper', which in turn executes `program', AFTER having issued a setuid(geteuid()) to set the REAL uid to the EFFECTIVE uid. Scheme: real uid - effective uid shell script user news > wrapper user news | v news news >> program news news >>> mkdir news root Of course `program' could do the setuid() as well. -- "I HATE arbitrary limits, especially when |Maarten Litmaath @ VU Amsterdam: they're small." (Stephen Savitzky) |maart@cs.vu.nl, mcvax!botter!maart
clewis@eci386.uucp (Chris Lewis) (06/15/89)
In article <2733@piraat.cs.vu.nl> maart@cs.vu.nl (Maarten Litmaath) writes: >tony@ajfcal.UUCP (Tony Field) writes: >\Is there any way to do a setuid(geteuid()) when geteuid() != 0 ??? >setuid() to either geteuid() or getuid() must ALWAYS succeed. Elementary. Maarten's usually right, but in this case he isn't. *Most* versions of UNIX (eg: Xenix and SV, but I think BSD may be the opposite) do not allow you to setuid() to anything other than getuid() unless geteuid() != 0. (SVID and System V also include something called the saved userid, but this doesn't apply here.). On the other hand, BSD can do this quite easily as Maarten suggests with things like seteuid() and setruid(). Maarten's right in the rest of his article (except for being able to in general say setuid(geteuid()), however... The easiest way to get a mkdir to get the ownership the way you want it is to write a setuid root wrapper that invokes mkdir and then chown's the created directory to "news" explicitly. eg, compile and make setuserid root: main(argc, argv) int argc; char **argv; { int pid; if ((pid = fork()) == 0) exec("/bin/mkdir", argv[1], 0); while(wait(0) != pid); exec("/bin/chown", "news", argv[1], 0); } (error checking and strong typing left as an exercise to the reader.) Grotty and inefficient but effective and small. -- Chris Lewis, R.H. Lathwell & Associates: Elegant Communications Inc. UUCP: {uunet!mnetor, utcsri!utzoo}!lsuc!eci386!clewis Phone: (416)-595-5425
clewis@eci386.uucp (Chris Lewis) (06/15/89)
In article <2733@piraat.cs.vu.nl> maart@cs.vu.nl (Maarten Litmaath) writes: >tony@ajfcal.UUCP (Tony Field) writes: >\Is there any way to do a setuid(geteuid()) when geteuid() != 0 ??? >setuid() to either geteuid() or getuid() must ALWAYS succeed. Elementary. Maarten's usually right, but in this case he isn't. *Most* versions of UNIX (eg: Xenix and SV, but I think BSD may be the opposite) do not allow you to setuid() to anything other than getuid() unless geteuid() == 0. (SVID and System V also include something called the saved userid, but this doesn't apply here.). On the other hand, BSD can do this quite easily as Maarten suggests with things like seteuid() and setruid(). Maarten's right in the rest of his article (except for being able to in general say setuid(geteuid()), however... The easiest way to get a mkdir to get the ownership the way you want it is to write a setuid root wrapper that invokes mkdir and then chown's the created directory to "news" explicitly. eg, compile and make setuserid root: main(argc, argv) int argc; char **argv; { int pid; if ((pid = fork()) == 0) exec("/bin/mkdir", argv[1], 0); while(wait(0) != pid); exec("/bin/chown", "news", argv[1], 0); } (error checking and strong typing left as an exercise to the reader.) Grotty and inefficient but effective and small. -- Chris Lewis, R.H. Lathwell & Associates: Elegant Communications Inc. UUCP: {uunet!mnetor, utcsri!utzoo}!lsuc!eci386!clewis Phone: (416)-595-5425 -- Chris Lewis, R.H. Lathwell & Associates: Elegant Communications Inc. UUCP: {uunet!mnetor, utcsri!utzoo}!lsuc!eci386!clewis Phone: (416)-595-5425
chip@ateng.com (Chip Salzenberg) (06/15/89)
According to tony@ajfcal.UUCP (Tony Field): >System: Xenix 2.2.3/386. >Is there any way to do a setuid(geteuid()) when geteuid() != 0 ??? No. Not only does "setuid(geteuid())" fail, but under SCO Xenix 2.3.1 at least, it returns ZERO when it fails. "Error codes? We don't need no stinking error codes!" -- You may redistribute this article only to those who may freely do likewise. Chip Salzenberg | <chip@ateng.com> or <uunet!ateng!chip> A T Engineering | Me? Speak for my company? Surely you jest!
skl@van-bc.UUCP (Samuel Lam) (10/10/89)
Could some setuid() or Xenix expert please help?
I am trying to port the letest (Rick Adams) version of the Berkeley FTP
server to run on SCO Xenix 386 2.3.2 and need to imitate the seteuid()
calls in the code with setuid()'s, since Xenix doesn't have seteuid().
What I need to be able to do is essentially the following:
- Start with euid(root).
- ...
- Switch to euid(arbitrary_uid).
- ...
- Revert back to euid(root).
- ...
Through the course of the program, the real uid can either remain
root or switches following the euid.
I have already spent part of the night trying out various schemes
which I thought would work, but none of them did -- I always had
trouble switching back to root after switching to the arbitrary
uid. Could someone tell me how this is done?
Thank you very much for your help.
...Sam
--
Samuel Lam <skl@wimsey.bc.ca> or {uunet,ubc-cs}!wimsey.bc.ca!skl