--- /dev/null
+ If we allowed the subu_home directory to be put anywhere, this script could be
+ used by masteru gain access to any directory on the system. Hence, we have
+ the following constraints:
+
+ constraint 1) the subu_home directory must not already exist, not as a
+ directory or as any other type of object.
+
+ constraint 2) masteru must have 'x' privledges to reach $(masteru_home)/subuland, and have
+ permissions to create the subu_home subdirectory.
+
+ constraint 3) subu_home may only be placed under the directory $(masteru_home)/subuland.
+
+ convention 4) only subu_home directories may be placed in $(masteru_home)/subuland.
+
+ -> without constraint 1), exploit 1
+
+ Suppose that a wily masteru was able to move an inaccessible directory that he
+ or she wanted access to and place it under $(masteru_home)/subuland.
+ Typically such directories are not moveable to wiley users in the first place,
+ but suppose the wily masteru found such a directory.
+
+ Alternatively suppose the wily masteru made a directory under $(masteru_home)/subuland
+ of his or her own, and placed an inaccessible file or subdirectory inside of it.
+
+ Alternatively suppose that the wily masteru made $(masteru_home)/subuland a hard link
+ or a symlink to a directory that contained a subdirectory that masteru did not have
+ access to.
+
+ The the wiley masteru could create a subu by the same name as the directory he desired
+ access to, and trick the foolish subu-mk-0 into giving him or her access.
+
+ -> without constraint 2) exploit 2
+
+ Then the masteru could place subu directories in places he can not access.
+ The foolish subu-mk-0 program would then add 'x' acls to as to reach this place.
+ The masteru could then change identity to the subu, (i.e. enter the container),
+ and then reach that place he or she could not reach before.
+
+ -> without constraint 3) exploit 3
+
+ There is still a wrinkle. If masteru looses x privlege to a place, subu might keep
+ it, and then exploit 2 would work despite the existence of constraint 2. It would
+ be unusual that masteru not have x privledges to masteru_home. Furthmore, we
+ degree that masteru has x privige to subuland. Hence, exploit 3 can be prevented
+ by following simple accounting rules that are already normal.
+
+ -> without convention 4) exploit 4
+
+ Constraint 4 is a convention that masteru
+
/usr/include/alloca.h /usr/include/bits/stdlib-bsearch.h \
/usr/include/bits/stdlib-float.h /usr/include/pwd.h \
/usr/include/string.h /usr/include/strings.h /usr/include/sys/stat.h \
- /usr/include/bits/stat.h /usr/include/bits/statx.h dispatch.lib.h \
- local_common.h ../config.h \
- /usr/lib/gcc/x86_64-redhat-linux/8/include/stdbool.h dbprintf.aux.h \
- dispatch_useradd.lib.h subu-mk-0.lib.h
+ /usr/include/bits/stat.h /usr/include/bits/statx.h \
+ /usr/lib/gcc/x86_64-redhat-linux/8/include/stdbool.h dispatch.lib.h \
+ local_common.h ../config.h dbprintf.aux.h dispatch_useradd.lib.h \
+ subu-mk-0.lib.h
/usr/include/stdc-predef.h:
/usr/include/bits/statx.h:
+/usr/lib/gcc/x86_64-redhat-linux/8/include/stdbool.h:
+
dispatch.lib.h:
local_common.h:
../config.h:
-/usr/lib/gcc/x86_64-redhat-linux/8/include/stdbool.h:
-
dbprintf.aux.h:
dispatch_useradd.lib.h:
+++ /dev/null
-/*
-fork/exec/wait a command
-
-if the error values returned by the exec'd program
-are less than 1 << 16, then
-
-*/
-
-// without this #define execvpe is undefined
-#define _GNU_SOURCE
-#include <sys/types.h>
-#include <unistd.h>
-
-#include <wait.h>
-#include <stdlib.h>
-#include <stdio.h>
-#include <errno.h>
-#include "local_common.h"
-#include "dispatch.lib.h"
-
-
-
-/*
- Execs the command passed in argv[0];
- Returns -1 upon failure.
-
- The wstatus returned from wait() might be either the error we returned when
- exec failed, or the return value from the command. An arbitary command is
- passed in, so we don't know what its return values might be. Consquently, we
- have no way of multiplexing a unique exec error code with the command return
- value within wstatus. If the prorgrammer knows the return values of the command
- passed in, and wants better behavior, he or she can spin a special version of
- dispatch for that command.
-*/
-int dispatch(char **argv, char **envp){
- if( !argv || !argv[0] ){
- fprintf(stderr, "argv[0] null. Null command passed into dispatch().\n");
- return -1;
- }
- #ifdef DEBUG
- dbprintf("dispatching:");
- char **apt = argv;
- while( apt ){
- dbprintf(" %s",*apt);
- apt++;
- }
- dbprintf("\n");
- #endif
- char *command = argv[0];
- pid_t pid = fork();
- if( pid == -1 ){
- fprintf(stderr, "fork() failed in dispatch().\n");
- return -1;
- }
- if( pid == 0 ){ // we are the child
- execvpe(command, argv, envp);
- // exec will only return if it has an error ..
- perror(command);
- return -1;
- }else{ // we are the parent
- int wstatus;
- waitpid(pid, &wstatus, 0);
- if(wstatus)
- return -1;
- else
- return 0;
- }
-}
+++ /dev/null
-#ifndef DISPATCH_LIB_H
-#define DISPATCH_LIB_H
-#include "local_common.h"
-
-int dispatch(char **argv, char **envp);
-
-#endif
-
-
--- /dev/null
+/*
+ fork/execs/wait the command passed in argv[0];
+ Returns -1 upon failure.
+
+ The wstatus returned from wait() might be either the error returned by exec
+ when it failed, or the return value from the command. An arbitary command is
+ passed in, so we don't know what its return values might be. Consquently, we
+ have no way of multiplexing a unique exec error code with the command return
+ value within wstatus. If the prorgrammer knows the return values of the
+ command passed in, and wants better behavior, he or she can spin a special
+ version of dispatch for that command.
+*/
+
+// without this #define execvpe is undefined
+#define _GNU_SOURCE
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <wait.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include "local_common.h"
+#include "dispatch_exec.lib.h"
+
+int dispatch_exec(char **argv, char **envp){
+ if( !argv || !argv[0] ){
+ fprintf(stderr, "argv[0] null. Null command passed into dispatch().\n");
+ return -1;
+ }
+ #ifdef DEBUG
+ dbprintf("dispatching exec:");
+ char **apt = argv;
+ while( apt ){
+ dbprintf(" %s",*apt);
+ apt++;
+ }
+ dbprintf("\n");
+ #endif
+ char *command = argv[0];
+ pid_t pid = fork();
+ if( pid == -1 ){
+ fprintf(stderr, "fork() failed in dispatch().\n");
+ return -1;
+ }
+ if( pid == 0 ){ // we are the child
+ execvpe(command, argv, envp);
+ // exec will only return if it has an error ..
+ perror(command);
+ return -1;
+ }else{ // we are the parent
+ int wstatus;
+ waitpid(pid, &wstatus, 0);
+ if(wstatus)
+ return -1;
+ else
+ return 0;
+ }
+}
--- /dev/null
+#ifndef DISPATCH_LIB_H
+#define DISPATCH_LIB_H
+#include "local_common.h"
+
+int dispatch_exec(char **argv, char **envp);
+
+#endif
+
+
--- /dev/null
+/*
+ changes the uid, gid, and forks and calls the function
+ Returns -1 upon failure.
+
+ The wstatus returned from wait() might be either the error returned by exec
+ when it failed, or the return value from the command. An arbitary command is
+ passed in, so we don't know what its return values might be. Consquently, we
+ have no way of multiplexing a unique exec error code with the command return
+ value within wstatus. If the prorgrammer knows the return values of the
+ command passed in, and wants better behavior, he or she can spin a special
+ version of dispatch for that command.
+*/
+
+// without this #define execvpe is undefined
+#define _GNU_SOURCE
+
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <wait.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include "local_common.h"
+#include "dispatch_f.lib.h"
+
+int dispatch_f(char *fname, int (*f)()){
+ char *perror_src = "displatch_f_as";
+ #ifdef DEBUG
+ dbprintf("%s %s\n", perror_src, fname);
+ #endif
+ pid_t pid = fork();
+ if( pid == -1 ){
+ perror(perror_src);
+ fprintf(stderr, "%s %s\n", perror_src, fname);
+ return ERR_FORK;
+ }
+ if( pid == 0 ){ // we are the child
+ int ret = (*f)();
+ return ret;
+ }else{ // we are the parent
+ int wstatus;
+ waitpid(pid, &wstatus, 0);
+ return wstatus;
+ }
+}
+
+int dispatch_f_euid_egid(char *fname, int (*f)(), uid_t euid, gid_t egid){
+ char *perror_src = "displatch_f_as";
+ #ifdef DEBUG
+ dbprintf("%s %s %u %u\n", perror_src, fname, euid, egid);
+ #endif
+ pid_t pid = fork();
+ if( pid == -1 ){
+ perror(perror_src);
+ fprintf(stderr, "%s %s %u %u\n", perror_src, fname, euid, egid);
+ return ERR_FORK;
+ }
+ if( pid == 0 ){ // we are the child
+ if( seteuid(euid) == -1 ){
+ perror(perror_src);
+ fprintf(stderr, "%s %s %u %u\n", perror_src, fname, euid, egid);
+ return ERR_SETEUID;
+ }
+ if( setegid(egid) == -1 ){
+ perror(perror_src);
+ fprintf(stderr, "%s %s %u %u\n", perror_src, fname, euid, egid);
+ return ERR_SETEGID;
+ }
+ int ret = (*f)();
+ return ret;
+ }else{ // we are the parent
+ int wstatus;
+ waitpid(pid, &wstatus, 0);
+ return wstatus;
+ }
+}
+
+
--- /dev/null
+#ifndef DISPATCH_LIB_H
+#define DISPATCH_LIB_H
+#include "local_common.h"
+
+#define ERR_FORK -1;
+#define ERR_SETEUID -2;
+#define ERR_SETEGID -3;
+
+int dispatch_f(char *fname, int (*f)());
+int dispatch_f_euid_egid(char *fname, int (*f)(), uid_t euid, gid_t egid);
+
+#endif
+
+
/*
Makes a new subu user.
- According to the man page, we are not alloed to free the memory allocated by getpwid().
+ According to the man page, we are not allowed to free the memory allocated by getpwid().
+ masteru is the user who ran this script. subu is the user being created.
-setfacl -m d:u:masteru:rwX,u:masteru:rwX subuname
+ subu-mk-0 is a setuid root script.
+
+ see also 3_doc/subu-mk-0.txt
*/
+
// without this #define we get the warning: implicit declaration of function ‘seteuid’/‘setegid’
#define _GNU_SOURCE
+
#include <sys/types.h>
#include <unistd.h>
-
#include <stdio.h>
+#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <pwd.h>
#include <string.h>
#include <sys/stat.h>
+#include <stdbool.h>
#include "dispatch.lib.h"
#include "dispatch_useradd.lib.h"
+#include "dispatch_f.lib.h"
#include "subu-mk-0.lib.h"
typedef unsigned int uint;
+/*
+ Fedora 29's sss_cache is checking the inherited uid instead of the effective
+ uid, so setuid root scripts will fail when calling sss_cache. Fedora 29's
+ 'useradd' calls sss_cache.
+
+*/
+#define BUG_SSS_CACHE_RUID 1
+
int subu_mk_0(char *subuname){
+ char *perror_src = "subu_mk_0";
+
//--------------------------------------------------------------------------------
#ifdef DEBUG
- dbprintf("Checking we are running from a user and are setuid root.\n");
+ dbprintf("Checking that we are running from a user and are setuid root.\n");
#endif
- uid_t uid = getuid();
- uid_t euid = geteuid();
- gid_t gid = getgid();
- gid_t egid = getegid();
+ uid_t master_uid = getuid();
+ gid_t master_gid = getgid();
+ uid_t set_euid = geteuid();
+ gid_t set_egid = getegid();
#ifdef DEBUG
- dbprintf("uid %u, gid %u, euid %u egid %u\n", uid, gid, euid, egid);
+ dbprintf("master_uid %u, master_gid %u, set_euid %u set_egid %u\n", master_uid, master_gid, set_euid, set_egid);
#endif
- if( uid == 0 || euid != 0 ){
+ if( master_uid == 0 || set_euid != 0 ){
fprintf(stderr, "this program must be run setuid root from a user account\n");
return ERR_SETUID_ROOT;
}
//--------------------------------------------------------------------------------
+ // recover the masteru user name from /etc/passwd
+
+ // char *subuname was passed in as an argument
size_t subuname_len;
char *masteru_name;
size_t masteru_name_len;
#endif
//--------------------------------------------------------------------------------
- // Just because masteru_home is referenced in /etc/passwd does not mean it exists.
+ // Just because masteru_home is referenced in /etc/passwd does not mean it exists,
+ // and does not mean that masteru owns it or has 'x' privileges.
// We also require that the subuland sub directory exists.
{
#ifdef DEBUG
dbprintf("checking that masteru_home and subuland exist\n");
#endif
struct stat st;
- if( stat(masteru_home, &st) == -1) {
- fprintf(stderr, "Strange, masteru home does not exist, \"%s\".", masteru_home);
+ int stat_ret;
+
+ stat_ret = stat(masteru_home, &st);
+ if( stat_ret == -1 ){
+ fprintf(stderr, "masteru home directory does not exist, \"%s\".", masteru_home);
+ free(subuland);
+ return ERR_NOT_EXIST_MASTERU_HOME;
+ }else if( !S_ISDIR(st.st_mode) ) {
+ fprintf(stderr, "strange masteru home directory is not a directory, \"%s\".", masteru_home);
free(subuland);
return ERR_NOT_EXIST_MASTERU_HOME;
+ }else if( ){
}
- if( stat(subuland, &st) == -1) {
- fprintf(stderr, "$masteru_home/subuland/ does not exist");
+
+ stat(subuland, &st);
+ if( !S_ISDIR(st.st_mode) ) {
+ fprintf(stderr, "$masteru_home/subuland/ directory does not exist");
free(subuland);
return ERR_NOT_EXIST_SUBULAND;
}
subuhome_len = subuland_len + subuname_len;
subuhome = (char *)malloc(subuhome_len + 1);
if( !subuhome ){
- perror("subu_mk_0");
+ perror(perror_src);
free(subuland);
return ERR_MALLOC;
}
strcpy (subuhome + subuland_len, subuname);
}
#ifdef DEBUG
- dbprintf("subuhome %s\n", subuhome);
+ dbprintf("subuhome: \"%s\"\n", subuhome);
#endif
/*--------------------------------------------------------------------------------
-d, --home-dir HOME_DIR The new user will be created using HOME_DIR
as the value for the user's login directory. ... The directory HOME_DIR
does not have to exist but will not be created if it is missing.
+
+ Actually Fedora 29's 'useradd' is making the directory even when -d is specified.
+ Adding the -M option supresses it.
*/
+
uid_t subuuid;
gid_t subugid;
+ bool subuhome_already_exists = false;
{
#ifdef DEBUG
- dbprintf("making subu\n");
+ dbprintf("making subu\n");
#endif
+
+ #if BUG_SSS_CACHE_RUID
+ if( setuid(0) == -1 ){
+ perror(perror_src);
+ return ERR_BUG_SSS;
+ }
+ #endif
+ struct stat st;
+ if( stat(subuhome, &st) != -1 ){
+ if( !S_ISDIR(st.st_mode) ) {
+ subuhome_already_exists = true;
+ }else{
+ fprintf(stderr, "Home directory would clobber non-directory object already at %s\n", subuhome);
+ return ERR_MK_SUBUHOME;
+ }}
+
char *command = "/usr/sbin/useradd";
- char *argv[5];
+ char *argv[6];
argv[0] = command;
argv[1] = subuname;
argv[2] = "-d";
argv[3] = subuhome;
- argv[4] = (char *) NULL;
+ argv[4] = -M
+ argv[5] = (char *) NULL;
char *envp[1];
envp[0] = (char *) NULL;
struct dispatch_useradd_ret_t ret;
}
subuuid = ret.pw_record->pw_uid;
subugid = ret.pw_record->pw_gid;
+ bool err_mk_subuhome = false;
+ if( !subuhome_already_exists && stat(subuhome, &st) != -1 ){
+ if( S_ISDIR(st.st_mode) ){
+ #if !BUG_USERADD_ALWAYS_MKHOME
+ err_mk_subuhome = true;
+ fprintf(stderr, "useradd -d unexpectedly created the subuhome, will delete that now\n");
+ #endif
+ if( rmdir(subuhome) == -1 ){
+ err_mk_subuhome = true;
+ fprintf(stderr, "could not delete the subuhome created by useradd, bailing\n");
+ return ERR_MK_SUBUHOME;
+ }
+ }else{
+ err_mk_subuhome = true;
+ fprintf(stderr, "useradd, or a parallel running process, has created a non-directory object at subuhome\n");
+ return ERR_MK_SUBUHOME;
+ }}
+
+ if( err_mk_subuhome )
+ fprintf(stderr, "encountered some difficulties when attempging to make subu, you better have a look\n");
+
#ifdef DEBUG
- dbprintf("subu made without errors\n", command, subuname, subuhome);
+ if( err_mk_subuhome )
+ dbprintf("useradd finished");
+ else
+ dbprintf("useradd finished with no errors\n");
#endif
}
#endif
int ret = mkdir(subuhome, 0x0700);
if( ret == -1 ){
- perror("subu_mk_0");
+ perror(perror_src);
free(subuland);
free(subuhome);
return ERR_MK_SUBUHOME;
}
ret = chown(subuhome, subuuid, subugid);
if( ret == -1 ){
- perror("subu_mk_0");
+ perror(perror_src);
free(subuland);
free(subuhome);
return ERR_MK_SUBUHOME;
#define ERR_FAILED_USERADD 8
#define ERR_SETFACL 9
#define ERR_MALLOC 10
-#define ERR_MK_SUBUHOME 11
+#define ERR_BUG_SSS 11
+#define ERR_MK_SUBUHOME 12
int subu_mk_0(char *subuname);
--- /dev/null
+
+#include <stdio.h>
+#include <unistd.h>
+int main(){
+ int retval = rmdir("/home/morpheus/subuland/ttemp0");
+ printf("retval %d\n",retval);
+ return 0;
+}
projects / subu / commitdiff