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* Check that the caller is allowed to call the setuid helper. The

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allowed uid is specified in a configuration file in
  /etc/nix-setuid.conf.
This commit is contained in:
Eelco Dolstra 2006-12-06 22:45:41 +00:00
parent 173d328351
commit f07ac41656
1 changed files with 50 additions and 13 deletions
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63
src/nix-setuid-helper/main.cc
View file

@ -1,6 +1,7 @@
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <pwd.h>
@ -25,20 +26,26 @@ static void secureChown(uid_t uidTarget, gid_t gidTarget,
}
static void runBuilder(string userName,
string program, int argc, char * * argv)
static uid_t nameToUid(const string & userName)
{
struct passwd * pw = getpwnam(userName.c_str());
if (!pw)
throw Error(format("the user `%1%' does not exist") % userName);
throw Error(format("user `%1%' does not exist") % userName);
return pw->pw_uid;
}
static void runBuilder(const string & targetUser,
string program, int argc, char * * argv)
{
uid_t uidTargetUser = nameToUid(targetUser);
gid_t gidBuilders = 1234;
/* Chown the current directory, *if* it is owned by the Nix
account. The idea is that the current directory is the
temporary build directory in /tmp or somewhere else, and we
don't want to create that directory here. */
secureChown(pw->pw_uid, gidBuilders, ".");
secureChown(uidTargetUser, gidBuilders, ".");
/* Set the real, effective and saved gid. Must be done before
@ -48,9 +55,9 @@ static void runBuilder(string userName,
//setgid(gidBuilders);
/* Set the real, effective and saved uid. */
if (setuid(pw->pw_uid) == -1 ||
getuid() != pw->pw_uid ||
geteuid() != pw->pw_uid)
if (setuid(uidTargetUser) == -1 ||
getuid() != uidTargetUser ||
geteuid() != uidTargetUser)
throw SysError("setuid failed");
/* Execute the program. */
@ -65,6 +72,11 @@ static void runBuilder(string userName,
}
#ifndef NIX_SETUID_CONFIG_FILE
#define NIX_SETUID_CONFIG_FILE "/etc/nix-setuid.conf"
#endif
static void run(int argc, char * * argv)
{
char * * oldEnviron = environ;
@ -83,13 +95,38 @@ static void run(int argc, char * * argv)
processes run (i.e., the supposed caller). It should match our
real uid. The second is the Unix group to which the Nix
builders belong (and nothing else!). */
/* !!! */
/* Make sure that we are called by the Nix account, not by someone
else. */
// ...
string configFile = NIX_SETUID_CONFIG_FILE;
AutoCloseFD fdConfig = open(configFile.c_str(), O_RDONLY);
if (fdConfig == -1)
throw SysError(format("opening `%1%'") % configFile);
/* Config file should be owned by root. */
struct stat st;
if (fstat(fdConfig, &st) == -1) throw SysError("statting file");
if (st.st_uid != 0)
throw Error(format("`%1%' not owned by root") % configFile);
if (st.st_mode & (S_IWGRP | S_IWOTH))
throw Error(format("`%1%' should not be group or world-writable") % configFile);
Strings tokens = tokenizeString(readFile(fdConfig));
fdConfig.close();
if (tokens.size() != 2)
throw Error(format("parse error in `%1%'") % configFile);
Strings::iterator i = tokens.begin();
string allowedUser = *i++;
string buildUsersGroup = *i++;
/* Check that the caller (real uid) is the one allowed to call
this program. */
uid_t uidAllowedUser = nameToUid(allowedUser);
if (uidAllowedUser != getuid())
throw Error("you are not allowed to call this program, go away");
/* Perform the desired command. */
if (argc < 2)
throw Error("invalid arguments");