X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?a=blobdiff_plain;f=cprogs%2Freally.c;fp=cprogs%2Freally.c;h=b240ea4702fce00157d2dca9566380aa87d4ac5f;hb=c314690b25b449e079fce8b215a3e96924898578;hp=0000000000000000000000000000000000000000;hpb=2e1bf919b1398410eb37c2398890b795028328bd;p=chiark-utils.git

diff --git a/cprogs/really.c b/cprogs/really.c
new file mode 100644
index 0000000..b240ea4
--- /dev/null
+++ b/cprogs/really.c
@@ -0,0 +1,210 @@
+/**/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <unistd.h>
+#include <pwd.h>
+#include <grp.h>
+#include <errno.h>
+#include <sys/types.h>
+
+#include "myopt.h"
+
+void usagemessage(void) {
+  if (fputs("usage: really [<user-option>] [<group-option> ...] [--]"
+            " [<command> [<argument/option> ...]]\n"
+            "user-options:\n"
+            " if no options given, set the uid to 0;\n"
+            " -u|--user <username>     also sets their default group list\n"
+            " -i|--useronly <username> } set the uid\n"
+            " -I|--uidonly <uid>       }  but inherits the group list\n"
+            "group-options:\n"
+            " -z|--groupsclear         only groups specified are to be used\n"
+            " -g|--group <groupname>   } add this to\n"
+            " -G|--gid <gid>           }  the group list\n",
+            stderr) == EOF) { perror("write usage"); exit(-1); }
+}
+
+static const char *opt_user, *opt_useronly;
+static int opt_groupsclear= 0, opt_ngids= 0, opt_uidonly= -1;
+static int opt_gids[512];
+
+static void af_group(const struct cmdinfo *cip, const char *value) {
+  struct group *gr;
+
+  if (opt_ngids >= sizeof(opt_gids)/sizeof(opt_gids[0]))
+    badusage("too many groups specified");
+  gr= getgrnam(value);
+  if (!gr) { fprintf(stderr,"unknown group `%s'\n",value); exit(-1); }
+  opt_gids[opt_ngids++]= gr->gr_gid;
+}
+
+static void af_gid(const struct cmdinfo *cip, const char *value) {
+  char *ep;
+  unsigned long ul;
+
+  if (opt_ngids >= sizeof(opt_gids)/sizeof(opt_gids[0]))
+    badusage("too many gids specified");
+  ul= strtoul(value,&ep,0);
+  if ((*ep) || (uid_t)ul != ul || ul>INT_MAX) badusage("bad gid `%s'",value);
+  opt_gids[opt_ngids++]= ul;
+}
+
+static void af_help(const struct cmdinfo *cip, const char *value) {
+  usagemessage(); exit(0);
+}
+
+static const struct cmdinfo cmdinfos[]= {
+  { "user",         'u',  1,  0, &opt_user,          0,           },
+  { "useronly",     'i',  1,  0, &opt_useronly,      0            },
+  { "uidonly",      'I',  1,  &opt_uidonly, 0,       0            },
+  { "groupsclear",  'z',  0,  &opt_groupsclear, 0,   0,        1  },
+  { "group",        'g',  1,  0, 0,                  af_group     },
+  { "gid",          'G',  1,  0, 0,                  af_gid       },
+  { "help",         'h',  0,  0, 0,                  af_help      },
+  {  0,              0                                            }
+};
+
+#ifdef REALLY_CHECK_FILE
+static void checkroot(void) {
+  int r;
+  r= access(REALLY_CHECK_FILE,W_OK);
+  if (r) { perror("sorry"); exit(-1); }
+}
+#endif
+#ifdef REALLY_CHECK_GID
+static void checkroot(void) {
+  gid_t groups[512];
+  int r;
+
+  r= getgid(); if (r==REALLY_CHECK_GID) return;
+  if (r<0) { perror("getgid check"); exit(-1); }
+  r= getgroups(sizeof(groups)/sizeof(groups[0]),groups);
+  if (r<0) { perror("getgroups check"); exit(-1); }
+  for (i=0; i<r; i++)
+    if (groups[i] == REALLY_CHECK_GID) return;
+  fputs("sorry\n",stderr); exit(-1);
+}
+#endif
+#ifdef REALLY_CHECK_NONE
+static void checkroot(void) {
+}
+#endif
+
+int main(int argc, const char *const *argv) {
+  struct passwd *pw= 0;
+  gid_t groups[512];
+  int i, j, ngroups, ngroups_in, maingid, orgmaingid, mainuid, orgmainuid, r;
+  const char *cp;
+  
+  checkroot();
+  myopt(&argv,cmdinfos);
+
+  if (opt_groupsclear && !opt_ngids)
+    badusage("-z|--groupsclear must be accompanied by some groups");
+  if (opt_user && (opt_useronly || opt_uidonly!=-1))
+    badusage("-u|--user may not be used with -i|--useronly or -I|--uidonly");
+  if (opt_user && opt_groupsclear)
+    badusage("-u|--user may not be used with -z|--groupsclear");
+  if (opt_uidonly != -1 && (uid_t)opt_uidonly != opt_uidonly)
+    badusage("-I|--uidonly value %d is out of range for a uid",opt_uidonly);
+
+  if (!opt_user && !opt_useronly && opt_uidonly==-1 && !opt_ngids) {
+    opt_uidonly= 0;
+  }
+  if (opt_user || opt_useronly) {
+    cp= opt_user ? opt_user : opt_useronly;
+    pw= getpwnam(cp);
+    if (!pw) { fprintf(stderr,"unknown user `%s'\n",cp); exit(-1); }
+    opt_uidonly= pw->pw_uid;
+  }
+  orgmaingid= getgid();
+  orgmainuid= getuid();
+  if (orgmaingid<0) { perror("getgid failed"); exit(-1); }
+  if (opt_user) {
+    r= initgroups(opt_user,pw->pw_gid);
+    if (r) { perror("initgroups failed"); exit(-1); }
+    maingid= pw->pw_gid;
+  } else {
+    maingid= -1;
+  }
+  if (opt_groupsclear) {
+    ngroups= 0;
+    if (opt_ngids > sizeof(groups)/sizeof(groups[0])) {
+      fputs("too many groups to set\n",stderr);
+      exit(-1);
+    }
+  } else {
+    ngroups= getgroups(0,0);
+    if (ngroups<0) { perror("getgroups(0,0) failed"); exit(-1); }
+    if (ngroups+opt_ngids > sizeof(groups)/sizeof(groups[0])) {
+      fputs("too many groups already set for total to fit\n",stderr);
+      exit(-1);
+    }
+    ngroups= getgroups(ngroups,groups);
+    if (ngroups<0) { perror("getgroups failed"); exit(-1); }
+  }
+  if (opt_ngids) {
+    maingid= opt_gids[0];
+  }
+  if (opt_ngids || opt_groupsclear) {
+    ngroups_in= ngroups; ngroups= 0;
+    for (i=0; i<ngroups_in; i++) {
+      for (j=0; j<ngroups && groups[j] != groups[i]; j++);
+      if (j<ngroups) continue;
+      groups[ngroups++]= groups[i];
+    }
+    for (i=0; i<opt_ngids; i++) {
+      for (j=0; j<ngroups && groups[j] != opt_gids[i]; j++);
+      if (j<ngroups) continue;
+      groups[ngroups++]= opt_gids[i];
+    }
+    r= setgroups(ngroups,groups);
+    if (r) { perror("setgroups failed"); exit(-1); }
+  }
+  if (maingid != -1) {
+    r= setgid(maingid); if (r) { perror("setgid failed"); exit(-1); }
+    r= setgid(maingid); if (r) { perror("2nd setgid failed"); exit(-1); }
+  }
+  if (opt_uidonly != -1) {
+    mainuid= opt_uidonly;
+  } else {
+    mainuid= orgmainuid;
+  }
+  r= setuid(mainuid); if (r) { perror("setuid failed"); exit(-1); }
+  r= setuid(mainuid); if (r) { perror("2nd setuid failed"); exit(-1); }
+  if (mainuid != 0) {
+    r= seteuid(0); if (r>=0) { fputs("could seteuid 0",stderr); exit(-1); }
+    if (errno != EPERM) {
+      perror("unexpected failure mode for seteuid 0"); exit(-1);
+    }
+  }
+  r= getuid(); if (r<0) { perror("getuid failed"); exit(-1); }
+  if (r != mainuid) { fputs("getuid mismatch",stderr); exit(-1); }
+  r= geteuid(); if (r<0) { perror("geteuid failed"); exit(-1); }
+  if (r != mainuid) { fputs("geteuid mismatch",stderr); exit(-1); }
+  if (maingid != -1) {
+    for (i=0; i<ngroups && maingid != groups[i]; i++);
+    if (i>=ngroups && maingid != orgmaingid) {
+      r= setgid(orgmaingid);
+      if (r>=0) { fputs("could setgid back",stderr); exit(-1); }
+      if (errno != EPERM) {
+        perror("unexpected failure mode for setgid back"); exit(-1);
+      }
+    }
+    r= getgid(); if (r<0) { perror("getgid failed"); exit(-1); }
+    if (r != maingid) { fputs("getgid mismatch",stderr); exit(-1); }
+    r= getegid(); if (r<0) { perror("getegid failed"); exit(-1); }
+    if (r != maingid) { fputs("getegid mismatch",stderr); exit(-1); }
+  }
+  if (!*argv) {
+    cp= getenv("SHELL");
+    if (!cp) cp= "sh";
+    execlp(cp,cp,"-i",(const char*)0);
+  } else {
+    execvp(argv[0],(char**)argv);
+  }
+  perror("exec failed");
+  exit(-1);
+}