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Full Discussion: Kill all process by UID
Top Forums UNIX for Advanced & Expert Users Kill all process by UID Post 302560977 by alister on Sunday 2nd of October 2011 05:02:13 PM
Old 10-02-2011
Quote:
Originally Posted by DendyGamer
Is there any secure way to kill all processes with specified UID ?
Traditional way like

setuid(WANTED_UID);
kill(-1,SIGKILL);

is not secure, because this programm will receive signals between calling setuid and calling kill (so, any programm with WANTED_UID can kill this "killer-program", because we cannot catch SIGKILL from process we try to kill).
You haven't provided any information regarding the ruid, euid, and suid of killer-program nor of its victims. However, it's possible that the only reason that killer-program is vulnerable is because of the setuid() call you're using.

A process p cannot send a signal to a process q unless p's real uid or effective uid matches either q's real uid or saved set uid.

Assuming that killer-program is privileged and starts with ruid==euid==suid==0, setuid(WANTED_GUID) will set them all to WANTED_GUID.

Assuming that the victims are running with ruid==euid==suid==WANTED_GUID, the victims can now kill killer-program because killer-programs ruid and/or suid matches victims' ruid and/or euid.

However, if instead you only modified killer-program's credentials so that ruid==suid==0 and euid==WANTED_GUID, the victims could not kill killer-program, since the victims' ruid and/or euid does not match killer-program's ruid and/or suid.

In short, if the assumptions are correct, all you need is to use seteuid instead of setuid.

If the uid assumptions are incorrect, then please be more specific.

Regards,
Alister
Last edited by alister; 10-02-2011 at 06:12 PM..
 

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LEARN ABOUT HPUX

setresgid

setresuid(2)							System Calls Manual						      setresuid(2)

NAME

       setresuid, setresgid - set real, effective, and saved user and group IDs

SYNOPSIS

DESCRIPTION

       sets the real, effective and/or saved user ID of the calling process.

       If  the	current  real,	effective  or saved user ID is equal to that of a user having appropriate privileges, sets the real, effective and
       saved user IDs to ruid, euid, and suid, respectively.  Otherwise, only sets the real, effective, and saved user IDs if ruid, euid, and suid
       each match at least one of the current real, effective, or saved user IDs.

       If ruid, euid, or suid is leaves the current real, effective or saved user ID unchanged.

       sets the real, effective and/or saved group ID of the calling process.

       If  the	current  real,	effective or saved user ID is equal to that of a user having appropriate privileges, sets the real, effective, and
       saved group ID to rgid, egid, and sgid, respectively.  Otherwise, only sets the real, effective and saved group ID if rgid, egid, and  sgid
       each match at least one of the current real, effective or saved group ID.

       If rgid, egid, or sgid is leaves the current real, effective or saved group ID unchanged.

   Security Restrictions
       Some  or  all  of  the actions associated with this system call require the privilege (CHSUBJIDENT).  Processes owned by the superuser will
       have this privilege.  Processes owned by other users may have this privilege, depending on system configuration.

       See privileges(5) for more information about privileged access on systems that support fine-grained privileges.

RETURN VALUE

       Upon successful completion, and return 0; otherwise, they return -1 and set to indicate the error.

ERRORS

       and fail if any of the following conditions are encountered:

	      ruid,	     euid, or suid (rgid, egid, or sgid) is not a valid user (group) ID.

	      None of the conditions above are met.

AUTHOR

       and were developed by HP.

SEE ALSO

       exec(2), getuid(2), setuid(2), privileges(5).

																      setresuid(2)
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